IET Electrical Measurement Series 8
A Handbook for
EMC
Testing and Measurement
David Morgan
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Contents
Foreword
1 Nature and origins of electrom.agnetic com.patibility
1.1
1.2
1.3
1.4
1.5
1.6
2
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
Definitions of electromagnetic compatibility
Visualising the EMI problem
1.2.1 Sources of EMI
1.2.2 EMI coupling to victim equipments
1.2.3 Intersystem and intrasystem EMI
Historical background
1.3.1 Early EMC problems
1.3.2 Early EMC problems with military equipment
1.3.3 The cost of EMC
1.3.4 Serious EMI problems
Technical disciplines and knowledge areas within EMC
1.4.1 Electrical engineering
1.4.2 Physics
1.4.3 Mathematical modelling
1.4.4 Limited chemical knowledge
1.4.5 Systems engineering
1.4.6 Legal aspects of EMC
1.4.7 Test laboratories
1.4.8 Quality assurance: total quality management
1.4.9 Practical skills
Philosophy of EMC
References
EMC standards and specifications
The need for standards and specifications
2.1.1 Background
2.1.2 Contents of standards
2.1.3 The need to meet EMC standards
Civil and military standards
2.2.1 Range of EMC standards in use
2.2.2 Derivation of military standards
2.2.3 Derivation of commercial standards
2.2.4 Generation of CENELEC EMC standards
UK/European commercial standards
2.3.1 UK standards relating to commercial equipment
2.3.2 Comparing tests
2.3.3 European commercial standards
2.3.4 German standards
US commercial standards
2.4.1 US organisations involved with EMC
2.4.2 FCC requirements
2.4.3 Other US commercial standards
Commercial EMC standards inJapan and Canada
2.5.1 Japanese EMC standards
2.5.2 Canadian EMC standards
Product safety
2.6.1 Safety of electrical devices
2.6.2 Product safety
2.6.3 Radiation hazards to humans
2.6.4 Hazards of electromagnetic radiation to ordnance
ESD and transients
2.7.1 ESD (electrostatic discharge)
2.7.2 Transients and power line disturbances
US military EMC standards
2.8.1 MIL STD 461/462/463
2.8.2 MIL-E-6051 D
2.8.3 Other US military standards
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2.10
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A HANDBOOK FOR EMC TESTING AND MEASUREMENT
UK military standards
2.9.1 Service and establishment-specific standards
2.9.2 Project-specific standards
2.9.3 DEF STAN 59-41 (1.988)
Following chapters
References
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3 Outline of EMC testing
3.1
Types of EM C testing
3.1.1 Development testing
3.1.2 Measurement to verify modelling results
3.1.3 Preconformance test measurements
3.1.4 Conformance testing
3.1.5 Conforrnance test plan
3.2
Repeatability in EMC testing
3.2.1 Need for repeatability and accuracy
3.2.2 Accuracy of EMC measurements
3.2.3 Implications of repeatability of EMC measurements
3.3
Introduction to EMC test sensors, couplers and antennas
3.3.1 EMC sensor groups
3.3.2 Conduction and induction couplers
3.3.3 Radiative coupling
EMC antennas
3.4
References
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Measurem.ent devices for conducted EMI
Introduction
Measurement by direct connection
4.2.1 Line impedance stabilisation network
4.2.2 10 flF feed through capacitor
4.2.3 RF coupling capacitors
4.2.4 Distributed capacitance couplers
4.2.5 High-impedance RF voltage probes
4.2.6 Directly connected transformers
4.3
Inductively coupled devices
4.3.1 Cable current probes
4.3.2 Current injection probes
4.3.3 Close magnetic field probes
4.3.4 Surface current probes
4.3.5 Cable RF current clamps
4.3.6 Magnetic induction tests
4.4
References
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Introduction to antennas
EMC antennas
EMC antenna basics
5.2.1 Arbitrary antennas
5.2.2 EMC antennas
5.3
Basic antenna parameters
5.3.1 Gain
5.3.2 Aperture
5.3.3 Transmitting antenna factor
5.3.4 Receiving antenna factor
5.3.5 Antenna phase centre
5.3.6 Mutual antenna coupling
5.3.7 Wavefield impedance
5.3.8 Near-field/far-field boundary
5.3.9 Beamwidth
5.3.10 Spot size
5.3.11 Effective length
5.3.12 Polarisation
5.3.13 Bandwidth
5.3.14 Input impedance
5.4
References
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4.1
4.2
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5.1
5.2
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CONTENTS
6
Antennas for radiated emission testing
6.1
6.2
6.3
6.4
6.5
6.6
6.7
6.8
6.9
6.10
6.11
6.12
6.13
Passive monopoles
6.1.1 Construction
6.1.2 Performance
Active monopoles
6.2.1 Advantages
6.2.2 Disadvantages
Tuned dipoles
6.3.1 Introduction
6.3.2 Practical tuned dipoles
6.3.3 Commercial EMC tuned dipoles
6.3.4 Radiated emission testing
Electrically short dipoles
6.4.1 Special short calibration dipoles
6.4.2 Roberts dipoles
6.4.3 Small nonresonant dipoles
6.4.4 Microscopic dipole probes
Biconic dipoles
6.5.1 Introduction
6.5.2 Commercial biconic antennas
6.5.3 Use of biconic antennas
Wideband antennas
6.6.1 Introduction
6.6.2 Log-periodic antenna
Log-periodic dipole antenna
Conical log-spiral antenna
Horn antennas
Ridged guide horn antennas
Reflector antennas
Magnetic field antennas
6.12.1 Introduction'
6.12.2 Passive loops
6.12.3 Active loops
6.12.4 Loop calibration
6.12.5 Magnetic field susceptibility tests
References
7 Use of antennas for radiated susceptibility testing
7.1
Introduction
7.1.1 Types of antennas used in susceptibility testing
7.1.2 Standards requiring immunity tests
Free-field antennas
7.2
Tuned halfwave dipoles
7.3
Biconic dipoles
7.4
Log-periodic dipoles
7.5
Conical log-spiral antennas
7.6
Horn antennas
7.7
Parabolic reflector antennas
Radiated immunity field strength requirements
7.8
7.8.1 Req uiremen ts for commercial products
7.8.2 Requirements for civil aircraft
7.8.3 Military requirements
7.9
E-field generators
7.9.1 Construction
7.9.2 Practical devices
7.10 Long wire lines
7.10.1 Advantages
7.10.2 Use in testing military equipment
Bounded-wave devices
7.11 Parallel-plate line
7.11.1 Properties
7.11.2 Line impedance
7.11.3 Construction
VB
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7.11.4 Complex lines
7.11.5 Field uniformity and VSWR
7.11.6 Use in screened room
7.12
7.13
7.14·
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TEM cells
7.12.1 Basic construction
7.12. 2 Crawford cell performance
7.12.3 Wave impedance in TEM cell
7.12.4 Field distortions in TEM cell
7.12.5 Other uses of TEM cells
7.12.6 Asymmetric TEM cells
GTEM cells
7.13.1 Description
7.13.2 Typical construction
7.13.3 Power req uiremen ts
7.13.4 GTEM cells used for emission testing
7.13.5 Pulse testing
References
Receivers, analysers and measurement equipment
Introduction
8.1.1 Outline of equipment
8.1.2 Groups of equipment
Instrumentation for emission testing
8.2
EMI receivers
8:2.1 Design requirements
8.2.2 Selectivity and sensitivity
8.2.3 Detectors
8.2.4 Commercially available EMI receivers
8.3
Spectrum analysers
8.3.1 Introduction
8.3.2 Analyser types
8.3.3 Analyser operation
8.4
Preselectors and filters
8.4.1 Preselectors
8.4.2 Bandlimiting filters
8.5
Impulse generators
8.5.1 Description
8.5.2 Design
8.5.3 Use of impulse generators
8.6
Digital storage oscilloscopes
8.6.1 Advan tages of digi tal oscilloscopes
8.6.2 Typical waveforms to be measured
8.6.3 Recording injected pulses for immunity testing
8.6.4 Digital transient recorder architecture
8.7
AF IRF voltmeters
8.8
RF power meters
8.9
Frequency meters
Instrumentation for susceptibility testing
8.10 Signal sources
8.10.1 Signal synthesisers
8.10.2 Signal sweepers
8.10.3 Tracking generators
8.11 RF power amplifiers
8.11.1 Introduction
8.11.2 Specifying an amplifier
8.11.3 RF amplifiers - conclusions
8.12 Signal modulators
8.12.1 Modulation requirements
8.12.2 Built-in modulators
8.12.3 Arbitrary waveform generators
8.13 Directional couplers, circulators and isolators
8.13.1 Amplifier protection devices
8.1
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CONTENTS
8.14
8. 15
9
8.13.2 Directional couplers
8.13.3 Hybrid rings, circulators and isolators
conclusion
8.13.4 Protection devices
Automatic EMC testing
8.14.1 Introduction
8.14.2 Automated emission testing
8.14.3 Automated susceptibility testing
8.14.4 In the future?
References
EMC test regitnes and facilities
9.1
9.2
9.3
9.4
9.5
10
10.1
10.2
10.3
10.4
10.5
Introduction
9.1.1 Main test regimes
9.1.2 Special testing
EMC testing in screened chambers
9.2.1 Enclosed test chambers
9.2.2 Standard shielded enclosures
9.2.3 RF anechoic screened chambers
9.2.4 Mode-stirred chambers
9.2.5 Novel facilities
Open-range testing
9.3.1 Introduction
9.3.2 Test site
9.3.3 Testing procedures
9.3.4 Site calibration
9.3.5 Measurement repeatability
9.3.6 Comments on open-site testing
Low-level swept coupling and bulk current injection testing
9.4.1 Introduction
9.4.2 Low-level swept coupling
9.4.3 Bulk current injection
References
Electrotnagnetic transient testing
Introduction
10.1.1 Transient types
10.1.2 Continuous and transient signals
Fourier transforms
10.2.1 Introduction
10.2.2 The transform
10.2.3 Introducing phase
10.2.4 Fourier transform expressions
10.2.5 Impulse response
10.2.6 Convolution
10.2.7 Advantages of time-domain manipulation
ESD-electrostatic discharge
10.3.1 Introduction
10.3.2 The ESD event
10.3.3 Types ofESD
10.3.4 ESD-induced latent defects
10.3.5 Types of ESD test
10.3.6 Number of discharges per test
10.3.7 ESD test voltage levels
10.3.8 Assessing EDT performance
Nuclear electromagnetic pulse
10.4.1 Introduction
10.4.2 Types ofNEMP
10.4.3 Exoatmospheric pulse generation
10.4.4 NEMP induced currents
10.4.5 NEMP testing
Lightning impulses
IX
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A HANDBOOK FOR EMC TESTING AND MEASUREMENT
10.6
10.7
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10.5.1 Lightning environment
10.5.2 Defining the discharge
10.5.3 Effects on equipment
Transients and general power disturbances
10.6.1 Importance of power transients
10.6~2 Examples of power supply immunity standards
10.6.3 Summary
References
Uncertainty analysis: quality control and test facility certification
11.1
11.2
11.3
11.4
Introduction
Some definitions
Measurement factors
Random variables
11.4.1 Student's t-distribution
11.5 Systematic uncertainty
11.6 Combining random and systematic uncertainties
11. 7 Uncertainties in EMC measurements
11. 7.1 Contributions to measurement uncertainty
11.7.2 Identification of uncertainty factors
11. 7.3 Estimation of uncertainty values
11.7.4 Estimate of total uncertainty
11.8 Test laboratory measurement uncertainty
11.8.1 NAMAS
11.8.2 NAMAS and measurement uncertainty
11.8.3 Limits and production testing
11.9 NAMAS requirements for laboratory accreditation
11.9.1 Requirements for accreditation
11.9.2 Advantages of laboratory accreditation
11.10 References
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12.1
12.2
12.3
12.4
13
13.1
13.2
Designing to avoid EMC problem.s
Intrasystem and intersystem EMC
12.1.1 Intrasystem EMC
12.1.2 Design for formal EMC compliance
System-level EMC requirements
12.2.1 Top-level requirements
12.2.2 Determining EMC hardening requirement
12.2.3 Simple coupling models
12.2.4 Susceptibility hardening case study
12.2.5 Emission suppression requirement
12.2.6 System hardening flow diagram
12.2.7 Subsystem apportionment and balanced hardening
12.2.8 Staff support for EMC
Specific EMC design techniques
References
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Achieving product EMC: checklists for product developtnent and testing 238
Introduction
13.1.1 Chapter structure
13.1.2 Example adopted
13.1.3 Personal computers and information technology
Information about EMC
13.2.1 Customer sources
13.2.2 Regulatory authorities
13.2.3 Industry sources
13.2.4 Equipment, component and subsystem suppliers
13.2.5 Professional bodies and conferences
13.2.6 EMC consultants and training
13.2.7 Electronics and EMC technical press
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CONTENTS
13.3
13.4
13.5
13.6
13.7
13.8
Determining an EMC requirement
Developing an approach to EMC design
13.4. 1 Process flow chart
13.4.2 EMC strategy
13.4.3 Immunity first?
13.4.4 Example of EMC design process
Technical construction file
13.5.1 Routes to compliance
options
13.5.2 Circumstances requiring the generation of a technical file
13.5.3 Contents of a technical file
13.5.4 Report from a competent body
13.5.5 Testing or technical file?
Self certification
13.6.1 Need for an in-house facility
13.6.2 Gradual development
13.6.3 Estimates of facility cost
13.6.4 Turnkey facilities
Conclusion
References
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Appendix 1
1.1
Signal bandwid th definitions
1.2
UK EMC legislation (up to 1 January 1996)
1.3
European EMC standards
1.4
German decrees and standards
1.5
US EMC regulations and standards
1.6
German, North American and Japanese EMC standards
1.7
Electrical safety and electromagnetic radiation
1.8
Military EMC standards
1.9
Compendium of EMC and related standards
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271
Appendix 2
2.1
Modulation rules
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Appendix 3
3.1
NAMAS-accredited laboratories
3.2
Competent bodies
3.3
EMC consultancy and training
3.4
Useful publications on EMC
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Index
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Foreword
During the latter part of the 1980s the worldwide
interest in electromagnetic compatibility has
grown significantly in the electronics industry,
particularly in the commercial and domestic
equipment sectors. The field of electromagnetic
compatibility is a dynamic one, with continuous
evolution and change. This has accelerated in the
1990s with the introduction of the European
Community EMC directive which applies to
almost all electrotechnical equipment. The
Directive attempts to harmonise regulations in
member states concerned with EMC after 1992
(with a transition period up to 1996). Equipment
(including imports) must meet the new EMC standards before they can be legally offered for sale
within the EC.
This book is devised in the form of a handbook
concerned with most aspects of electromagnetic
compatibility and addresses in a single volume
many of the technical and managerial issues
which will be of concern to designers and manufacturers of commercial and military electronic
equipment. The primary focus of the "book is on
EMC testing and discusses the numerous test
methods in relation to the EMC standards for
which they are required.
Understanding EMC is important to produce
reliable interference-free products and understanding EMC testing is the key to demonstrating
that well designed equipment meets legislative
and contractual req uirements, including the new
EC regulations.
EMC grew in importance in the field of military
electronics over a 20-year period from abolit the
mid 1960s, and therefore has been a precursor to
the developments in the civil sector. Thus many
of the design techniq ues and some test methods
have been introduced into the field of commercial
electronics EMC from this military background.
Other test methods have developed entirely in
regard to commercial equipment and have no
counterpart in military EMC testing. This book
contains examples of many commercial and military EMC tests and shows how difficult it can be
to compare results from various tests which
purport to measure the same quantity.
Although the recent surge in interest in EMC
has been spurred in the commercial electronics
industry by the introduction of the EC Directive
on EMC, the interest of military electronics manufacturers in EMC is strong and still growing.
Many of the larger test facilities in the UK which
carry out testing of commercial and military electronics are operated by military/aerospace companies. For these reasons this book devotes a proper
proportion of space to discussing test methods and
specifications which relate to military equipment
EMC, and includes a brief section on nuclear electromagnetic pulse effects in a chapter concerned
with electromagnetic transients such as electrostatic discharge and lightning.
Electromagnetic compatibility engineering is a
multidisciplinary activity involving electrical engineers, physicists, chemists, systems and mechanical engineers and has quality, marketing and
legal implications in the management of electronic product development. This book has therefore been written with the aim of being accessible
to both technical staff and management. For
example, it has detailed technical sections on
basic antenna theory and EMC testing practice as
well as sections oriented towards management/
project control, concerned with regulations and
standards, and the EMC planning aspects of
product development.
1'he emphasis lies on EMC testing. Within the
text, test specifications, test methods and test
equipment are discussed in some detail. I t would
be cumbersome and impractical to explain each
test method in detail for the enormous range of
civil and military EMC specifications in use today
through the world. Therefore the technical material on testing has been constrained to presenting
the details of a number of generic types of test
and has been constructed around a description of
the physical principles and mechanisms which
underlie the measurements.
Information is presented for the following
generic types of test:
Radiated emission
Radiated susceptibility
Conducted emission
Conducted susceptibility
Transien t emissions (mainly conducted)
Transient susceptibility (including electrostatic
discharge)
The couplers, sensors and antennas used to make
these measurements are treated in groups defined
by the physical coupling mechanism they employ.
For example, conducted emission devices are
divided into direct connection probes, inductive
couplers and capacitive couplers. In this way,
some physical meaning and order is brought to
the construction and operation of the extensive
range of antennas and sensors used in EMC
testing.
Although it contains considerable technical
detail the material in this book has also been
chosen to give the reader who may be coming to
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XIV
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
the subject of electromagnetic compatibility for the
first time a broad view of the range of topics
covered by the s.ubject. The text therefore
includes sections on topics such as
The nature of electrical interference
Standards and specifications
Developing system and subsystem EMC requIrements
EMC design techniq.ues
The nature of EMC testing
Test methods
Measurement uncertainty
Quality control in test laboratories
Laboratory accreditation
Achieving EMC in new products
While the reader is encouraged to adopt a
straightforward reading path *, this material has
been organised to facilitate the selection and use
of particular chapters in the manner of a handbook for day-to-day use. Chapters 6 and 7 for
example contain useful antenna formulas which
may need to pe .accessed quite often by a practising EM C test engineer.
Where appropriate, small sections of the text
have been devoted to reviewing the theory which
underlies arguments which are to follow. This has
been done in Chapter 5 with some basic concepts
of antennas, and in Chapter 10 where an expla*It may be appropriate for readers who are new to EMC
to read Chapter 12 on EMC design after Chapter 2
(EMC standards). Chapter 12 contains a number of
concepts and insights into the causes and solutions of
EMC problems which may help the reader with the rest
of the book. The chapter on EMC design has been positioned towards the end of the book so as not to disrupt
the progression from the introduction followed by EMC
standards directly to the main focus of the book on
EMC testing.
nation of the mathematical relationship between
the frequency and time domains is given to enable
the reader to understand transient testing and to
be able to visualise the frequency content of waveforms.
For ease of reading, long lists or tables of information have been put into appendices at the end
of the book. This is particularly so for Chapter 2
on EMC standards where lists of standards, equipment classes and tests would otherwise break up
the flow.
Numerous examples of EMC standards from
around the world are included in Chapter 2.
These range from the earliest historical examples
to the recently issued and proposed European
Norm standards. EMC standards and test
methods are changing rapidly and whilst every
attempt has been made to include the most up-todate information, new standards are bound to be
issued and supersede existing ones.
I t is not possible to cover in a single book the
enormous range of information which constitutes
the current body of knowledge on EMC. The aim
here has been to provide an introduction to EMC
and particularly to EMC testing in the form of a
useful day-to-day handbook. There are many
other published texts, some in up to 12 volumes,
which deal in detail with the design aspects of
EMC. These are referenced in this text. With the
expansion of interest in EMC a number of useful
books have been written since 1990 which reflect
the dynamic nature of the topic. They are listed
in Chapter 13 along with information on the lEE
distance learning project on EMC.
I t is hoped that readers find this hand book
helpful, informative and easy to read and use. If
it helps to stimulate an interest in this fascinating
subject and direct the reader to sources of more
detailed information it will have achieved its
objective.
Acknowledgem.ents
Extracts from British Standards are reproduced
wi th the permission of BS I. Complete copies can
be obtained by post from BSI Sales, Linford
Wood, Milton Keynes, MK14 6LE.
Figures 5.12, 5.14 and 8.34 are from the book
'Reference data for engineers: radio, electronics,
computer and communications' edited by Mac
E. Van Valkenburg. Published by SAMS
Publishing,
a
division of Prentice Hall
Computer Publishing. Used by permission of
the pu blisher.
The publishers are grateful to Marconi
Instruments Ltd. for help in the cover design of
this book.
Chapter 1
Nature and origins of
electrom.agnetic com.patibility
1.1 Definitions of electroIllagnetic
cOIllpatibility
The formal definition of electromagnetic compatibility,
as
given
in
the
International
Electrotechnical Vocabulary (IEC 50) is: 'the
ability of a device, equipment or system to
function satisfactorily in its electromagnetic
environment without introducing intolerable electromagnetic disturbances to anything in that
environment' [1 J. A similar definition cited by
Duff [2J is given as: 'the ability of equipments
and systems to function as intended, without
degradation or malfunction in their intended
operational
electromagnetic
environments.
Further, the equipment or system should not
adversely affect the operation of~ or be affected
by, any other equipment or system'.
Electromagnetic interference (EMI) can be
viewed as a kind of environmental pollution
which
can
have
consequences
that
are
comparable to toxic chemical pollution, vehicle
exhaust emissions or other discharges into the
environmen t. The electromagnetic spectrum is a
natural resource which has been progressively
tapped by man over the last 100 years. Most of
the development has taken place in the last 50
years with the advent of public service broadcasting, point-to-point and mobile communications etc. which has brough t great economic and
social benefits. The spectrum is now almost full
and it is proving difficult to satisfy the pressures
for new uses of this resource. Modern life has
come to depend heavily on systems that use the
electromagnetic spectrum and its protection is in
the interests of us all. For this reason unwarranted
electromagnetic interference represents a real
economic and social threat which can even result
in injury or death.
Unfortunately,
electromagnetic interference
cannot be smelled, tasted or seen by either the lay
person who purchases electronic products or by
the corporate technical manager who has to
supervise the design of the latest electronic
product and get it to the marketplace as fast as
possible, for the lowest possible cost. There has,
therefore, been a tendency to deny that EMI is a
problem in the modern world and to argue that
the costs which are associated with achieving electromagnetic compatibility (EMC) need not be
borne. Some of these wider issues are explored
later, but for now another definition of this
fascinating and wide ranging concept is examined.
Keiser [3J defines EMC in this way: 'electrical
and electronic devices can be said to be electromagnetically compatible when the electrical noise
genera ted by each does not interfere wi th the
normal performance of any of the others. EMC is
that happy situation in which systems work as
intended, both within themselves and in their
environment' .
Electromagnetic
in terference
ind uces
undesirable voltages and curren ts in the circui ts of
the victim equipment. This can cause audible
noise in radio receivers and spots, snow or loss of
frame synchronisation on TV pictures. When
vital communications links, computer installations
or computer driven industrial process control
equipment is the victim equipment, more serious
conseq uences can occur.
Interference can reach the victim system by two
basic routes: conduction along cables, and electromagnetic radiation. This chapter examines typical
sources of EMI and discusses the technical basis of
electromagnetic
compatibility
within
an
equipment, and between the equipment and its
environmen t in terms of conducted and radiated
interference paths.
1.2 Visualising the EMI probletn
1.2.1 Sources of EM I
Any electrical or electronic device that has
changing voltages and currents can be a source of
EM!. If the culprit equipment has no cables
connecting it to the outside world, for example a
battery powered electric shaver, then the
interfering energy generated by sparking within
the electric motor can only travel as an electromagnetic wave. If the shaver is mains powered,
both radiated noise and interference conducted
along the cable into the mains wiring are possible.
This is illustrated in Figure 1.1 where a mains
powered shaver and a washing machine are both
2
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
HOUSE MAINS WIRING
~,.
EMI CURRENTS FLOW
INTO OTHER BUILDINGS
INTERFERENCE NOISE CURRENTS
"
)
,. Motor noise
)
J
Indirect radiation from
currents in mains cables
eo
o
Mains power'
waveform
Motors, switches
relays, etc.
/
~
~,V
\
'-)\
/
CULPRIT 1
ELECTRIC SHAVER
MOTOR
Figure 1.1
\ \
\
BU)D1NGlJ
)
DIRECT RADIATION FROM
ELECTRIC SHAVER (ALSO
RADIATES OUTSIDE
CULPRIT 2
WASHING MACHINE
TV receiver
is victim
Illustration of simple EMI problem
causing interference to a TV picture in an adjacent
room. Radiation is emitted not only directly from
the shaver or washing machine motor, but also
from the mains wiring which is carrying the
conducted radio frequency (RF) noise.
Generally, the faster the rate of change of voltage
or current in the culprit equipment, the wider is the
spectrum of RF interference produced. The greater
the magnitude of the noise voltages or currents the
greater will be the conducted and radiated
emissions. Therefore electric motors, which
generate high voltages and currents with fast
risetimes as the inductive coils in the rotor are
switched by the commutator, are good examples of
particularly powerful sources of EMI.
Other common sources of electromagnetic interference are given in Table 1.1
These sources can be grouped in terms of usage
as shown in Figure 1.2. They may be sources of
continuous or transient interference as shown in
Figure 1.3. Continuous sources include radio
transmi tters and emissions from RF heaters for
example where the signal is an uninterrupted
carrier, but also include pulsed systems such as
radars and the emissions from digital compu ters
which have wide but stable RF spectra. The
emissions from these sources are best measured
and analysed in terms of their spectral content
using narrow bandwidth scanning receivers or
spectrum analysers.
Table 1.1 Common sources of EM!
Powerline arcing" and corona discharge
Automobile ignition systems
Fluorescent lighting
Switched-mode power supplies
Portable electric generators
Static or rotary power converters
Any appliance using brush commutator motor
Air conditioning equipment
Computer equipment and peripherals
Equipment with switches and relays
Diathermy medical equipment
Arc-welding sets
High-voltage neon signs
Light dimmers
Microwave ovens
CB radio
Radar transmitters
Broadcast transmitters
Atmospherics (noise from lightning around the
world)
Whistlers, chorus and hiss from the magnetosphere
Nearby lightning storms
Precipitation static noise
Disturbed and quiet radio noise from the sun
Cosmic radio noise
NATURE AND ORIGINS OF ELECTROMAGNETIC COMPATIBILITY
3
SOURCES OF EMI
-BROADCAST STATION
-RADAR
-CBRADIO
-AMATEUR RADIO
-ELFNLF NAVIGATION/COMS
-MOBILE Tx
-REMOTE CONTROL DOOR
OPENING TRANSMITTERS
-POINT TO POINT HF COMS.
-IONOSPHERIC SCATTER
RADAR AND COMS.
- PORTABLE
POWER GENS.
- STATIC & ROTARY
CONVERTERS
- RECTIFIERS
- TRANSMISSION
LINE NOISE
- POWER FAULTS
- CONTACTORS
STATIC NOISE
}'igure 1.2
-AUTOMOBILES
& VEHICLES
-TRACTION
POWER
POWER
CONVERSION
-ELECTRIC
MOTIVE
POWER
-IGNITION
SYSTEMS
MOBILE Tx.
ATMOSPHERICS
- WORKSHOP
MACHINES
- COMPRESSORS
- ROTARY SAWS
- BALL MILLS
RF HEATERS
- ULTRASONIC
CLEANERS
- WELDERS
-SPARK EROSION
- CRANES I FANS
- OVENS IKILNS
SOLAR· NOISE
-DIELECTRIC
HEATERS
-AIR CONDITIONING
- COMPUTERS
-FLUORESCENT
LIGHTS
LASER SYSTEMS
NEON DISPLAYS
- MEDICAL EQUIP.
-PROCESS CONTROL
X RAY MACHINES
LIGHTNING
- MICROWAVE OVENS
- LIGHT DIMMERS
- PERSONAL COMPUTERS
- MIXERS/BLENDERS
- VACUUM CLEANERS
- WASHING MACHINES
- HAIR DRYERS
- ELECTRIC MODELS
- FRIDGESIFREEZERS
- SHAVERS
-THERMOSTATS
COSMIC RADIO BACKGROUND NOISE
(;roups oj EMI sources
Sources
of
transient
emISSIons
include
lightning, nuclear electromagnetic pulse, powerline faults, switch and relay operation, etc. They
are characterised by single or in termi tten t
occurrence at unpredictable times with no
significant time pattern. Often, the signals are of
short duration and hence have a wide signal
bandwidth. I t is easier to measure, record and
analyse such signals as a waveform in the time
domain.
rrhe
advent
of wide-bandwidth
transient-capture waveform digitisers and fast
transformation algorithms has only recently led
to the ability to view easily the spectrum of a
single fast transient.
The details of EMC test equipment and test
techniques that are capable of measuring the wide
range of interference signals from these EMI
sources are the main concerns of this book and
are to be found in Chapters 4 to 11.
ExaInples of the extent of the frequency
spectrum, repetition rates and signal amplitudes
from some typical EMI sources are given in
I'able 1.2 which contains both intended and
unintended sources of EM radiation.
Examples of approximate field strengths for
typical broadcast transmitters in the UK are
given in Figure 1.4 and for other sources in
Figure 1.5. These data with regard to emission
levels and freq uencies for potential sources of
ElYlI allow the appreciation of the potential scale
of the problem if such sources can couple to
sensitive victim equipment which may only be
able to tolerate a few microvolts or millivolts of
unwanted
SOURCES OF EMI
SOURCES OF CONTINUOUS EMI
(CONTINUOUS SPECTRUM OF NOISE)
• BROADCAST STATIONS
HIGH POWER RADAR
- ELECTRIC MOTOR NOISE
FIXED & MOBILE COMMUNICATIONS
COMPUTERS, VDUs & PRINTERS etc.
• AC I MULTIPHASE POWER RECTIFIERS
HIGH REPETITION RATE IGNITION NOISE
SOLAR AND COSMIC RADIO NOISE
BEST MEASURED AND ANALYSED IN THE
-FREQUENCY DOMAIN- - (SPECTRUM)
SOURCES OF TRANSIENT EMI
(COMPOSED OF SEPARATE PULSES)
- LIGHTNING
- NUCLEAR EMP
- POWER LINE FAULTS (SPARKING)
- SWITCHES AND RELAYS
ELECTRIC WELDING EQUIPMENT
- LOW REPETITION RATE IGNITION NOISE
ELECTRIC TRAIN POWER PICK-UP ARCING
- HUMAN ELECTROSTATIC DISCHARGE
BEST MEASURED AND ANALYSED IN THE
-TIME DOMAIN- - (WAVEFORM)
1.3 Sources oj~ continuous
and transient interference
4
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
Table 1.2 Frequencies and noise levels from typical interference sources
Source type
Comments
Mains disturbances
Double exponential transients with risetimes of 1 J.1S and fall times of 50 J.1S at
approx.10kV
100 kHz ringing waveform with 0.5 J.1S rising edge
Power dips up to 100 ms long
Power frequency harmonics up to 2 kHz
Unintended radiators
Switches and relays
Transients with risetimes of a few ns and levels up to 3 kv producing frequencies
into the VHF band
Commutator motors
Produce frequencies up to 300 MHz at repetition rates of up to 10 kHz
Human electrostatic
discharge
I-IOns risetime
30-200 ns fall time ampli tudes up to 15 kV
Switching
semiconductors
Risetimes from 20 to 1000 ns at rep rate of kHz to 10 MHz for voltages up to
300V
Switched-mode power
supplies
Produce continuous spectrum of noise from kHz to 100 MHz
Digital logic
Circuits produce continuous noise up to 500 MHz
Ind ustrial and medical
equipment
Metals heating in 1-199 kHz range.
Medical equipment operates from
13-40 MHz. Using high power-hundreds of watts
Intended radiators
Broadcast stations
See Figure 1.4
Other RF transmitters
including radar
See Figure 1.5
1000
180
Figure 1.4 Field
strengths in the
vicinity of broadcast
transmitters
170
160
-r
~
SHORT WAVE
dBuV/m
150
T
-r---l..- T TUHF
-
LONG WAVE
130
120 ....
--a.I
10k
Reproduced by permission of' BAe Dynamics Ltd.
......
I
100k
--L
.....I
~
1M
TV
VHF
MEDIUM WAVE
TELEGRAPHY
140
-
}VHFl
O
RAI
....
I
10M
FREQUENCY OF TRANSMITIER (Hz)
....
I
100M
100
T
Vim
UHF
TV
1-
10
.... 1
10
NATURE AND ORIGINS OF ELECTROMAGNETIC COMPATIBILITY
180
100m
RADAR
400m
170
CB Tx ON VEHICLES
160
-
AMATEUR TRANSMITIERS @ 10m
_/
150
I
1000
-
/
Figure 1.5 Field
strengths in the
vicinity oj other sources
100
~_/
dBuV/m
5
VIm
CB Tx (100w @ 10m)
140
f
f
RF HEATERS
~
10
LAND MOBILE BASE STATION
TRANSMITIERS @ 10m
130
CBTx 4w @ 10m
120
1M
3M
10M
30M
100M
FREQUENCY Hz
1.2.2 EMI coupling to victim equipments
An EMI problem can only exist if a source of
EMI, a culprit, is able to exchange electromagnetic energy with a receptor or victim equipment.
Thus the general EMI problem can be
represen ted by these three componen t~ as show.n
in Figure 1.6. The coupliI).g can be VIa metalhc
cond uctors such as power or signal cables, if they
exist, or more generally by electromagnetic
radiation from one equipment to the other.
Energy exchange will take place between th.e
electromagnetic wavefield produced by the culprIt
equipment, and metallic conductors attached to
the victim equipment which will have RF
currents induced in them. If the primary coupling
mode is radiative but the receptor has a cable
attached to it (but not connected to the culprit)
currents can be induced into the cable that will
then flow directly into the victim, even if it is
protected from direct radiation by a high
performance shielded case. See Figure 1.7 a.
RADIATION
SOURCE OF EMI
, RECEPTOR OF EMI
(Culprit equipment)
(Victim equipment)
CONDUCTION
SOURCE
Figure 1.6
COUPLING
RECEPTOR
Three components oj an EMC problem
300M
10
Reprod uced by permission of BAe
Dynamics Ltd,
Equally, if the primary coupling bet:ve.en
culprit and victim is conducted, but the vIctIm
has a good filter connected to the input cable,
the currents in the cable can still radiate EM
energy which may then couple into the victim if
it has no electromagnetic screening.
See
Figure 1.7 b. This situation demons't:ates that
both radiative and conducted couphng paths,
whether direct or indirect, must be addressed in
parallel if the EMI energy is to be preven te?
from reaching the victim equipment. ThIs
argument leads directly to .the. combi~ed
application of shielding and filterIng In practIcal
solutions to EMI problems. Common receptors
or victim equipments are listed in Table 1.3. The
list contains both intended and unintended
receivers.
Electromagnetic compatibility engineering is
composed of four basic topics as shown in
Figure 1.8 related to the combinations. of source/
victim and radiated/conducted couphng. EMC
standards and specifications often use the
following initials to describe these four elements:
RE
RS
CE
CS
-
radiated emission from a culprit
radiated susceptibility of a victim
conducted emission from' a culprit
conducted susceptibility of a victim
Because conducted and radiated transient EMI,
including electrostatic discharge (ESD) are
measured using different techniques, they are
sometimes represented as an additional fifth group,
6
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
Shield prevents direct radiative coupling
from culprit to victim ~
"Radiated EMI from culprit
/
VICTIM SYSTEM
CULPRIT SYSTEM
Input connector
\
RF CURRENTS CONDUCTED
INTO VICTIM
lamps \
~CABLE
ACTS ASAN UNWANTED IlANTENNA"
"TO OTHER EQUIPMENT
Induced RF EMI
current into cable
""-,
~-.
(aj
///~
POOR or NO SHIELD
~
1--I
Radiation reaches PCB /'
Radiation from the Cable
f //l
V~C~\STIEM ( :.L (
L -T
CIRCUITS DIRECTLY EXPOSED TO
RtATE~
-:MI
\
\
\
\~
\~
CULPRIT SYSTEM
lamps
(NO DIRECTLY RADIATED EMI)
, , ( s o u r c e of RF currents)
High le'el of CONDUCTED EMI
GOOD FILTER STOPS CONDUCTED EMI
(bj
Figure 1.7
( aj Radiated to conducted EMI (b j Radiation Jrom cable carrying EM1 currents
Table 1.3 E'xamples
of victims oj EMI
Intended receivers
Radio receivers 0.0 1-1 f1 V sensitivity
Broadcast receivers
TV receivers
Mobile communication receivers
Microwave relay systems
Mobile telephones
Aircraft communication receivers
N aviga tion aids
Radar receivers
[inintended receivers
Aircraft engine control systems
Aircraft flying surface con troIs
Weapons systems, guided missiles
Electronic ships systems inc steering gear
Video recording/playback equipment
Computer equipment
Industrial process control systems
Signalling systems
Medical electronic instruments
Heart pacemakers
Biological tissue
Ordnance and explosive fuses
as in Figure 1.8. RF hazards to fuels, explosives,
electrically detonated ordnance, and RF hazards
to biological tissue (including humans) can also be
encompassed within the general concept of electromagnetic compatibility.
EM C testing is carried ou t in all these areas,
though the measurement techniques and instrumentation vary widely depending on the
particular test. For RE and RS tests the
equipment under test (EDT) is placed at some
dis tance (usually 1 or 3 m) from a range of
antennas that are used either to measure the lowlevel EM emissions from the equipment, or to
generate high field strengths at the equipment for
susceptibility testing.
Cond ucted emission (CE) tests involve the use of
special coupling transformers or current probes to
sense the level ofRF current being conducted away
from the EDT along its cables. The conducted
susceptibili ty (CS) tests require RF current to be
injected into cables either using coupling transformers and probes or by direct connection.
The main body of this text is concerned with
explaining these test methods and examining in
detail the physical principles and operating
practice associated with the types of antennas,
current probes and other sensors used.
NATURE AND ORIGINS OF ELECTROMAGNETIC COMPATIBILITY
SAFETY OF ELECTRO-EXPLOSIVE
SAFETY OF NON-IONISING
DEVICES
___________...:------------1--------1
RADIATED EMISSIONS (RE)
10 Hz to 40 GHz
E FIELD 14kHz - 400Hz
H FIELD 10Hz - 30MHz
(LEVELS DOWN TO
-110dBV/m)
RADIATED SUSCEPTIBILITY (RS)
10Hz to 40 GHz
1 - 200V/m (CW)
NUCLEAR ELECTROMAGNETIC
PULSE
50kV/m RS (10/400ns)
100 A (DAMPED SINUSOID)
Figure 1.8
7
RADIATION ON BIOLOGICAL
TISSUE
CONDUCTED EMISSIONS (CE)
20Hz to 100 MHz CABLES
100MHz -4OGHz ANTENNA
CABLES
(LEVELS DOWN TO -120dBA)
MAINS DISTURBANCES
AND LIGHTNING
10kV TRANSIENTS
100ms DROPOUTS
HARMONIC DISTORTION
CONDUCTED SUSCEPTIBILITY (CS)
20Hz to 400MHz @ -2OdB VA
HUMAN ESD
15kV TRANSI ENTS
DIRECT & RADIATED
(5/30ns waveform)
Examples of EMG) and related activities
1.2.3 Intersystem and intrasystem EMI
EMC activity can also be differentiated in terms of
the level at which it is applied. The widest level
concerns the compatibility between a system of
interest and all other systems with which it could
interact, including the general EM environment.
This is called intersystem EMC and can involve
for example, frequency planning, equipment
siting, antenna sidelobe suppression and the
imposition of operating restrictions including
timing constraints. In the military world
operational restrictions might apply to the
minimum space between aircraft or the minimum
distance at which they may approach a ground
based transmitter.
The interaction of commercial civilian systems
with broadcast receivers and the general EM
environment is regulated largely by voluntary
trade agreements or government laws. The
advent of the widespread use of desktop digital
compu ters has forced the introd uction of
legislation to control the radiated and conducted
emissions from such equipments in order to
protect the broadcast spectrum.
Intrasystem EMC is concerned with the selfcompatibility of the system of interest. It relies on
the premise that if each individual unit within the
system is required to emit less EMI than any of
the units would be susceptible to, plus a margin
for safety, then when the units are assembled as a
whole the system will be electromagnetically
compatible.
The
overall
system
EMC
requirement must be determined and apportioned
to each subsystem or unit. The detailed design
work is then carried out at the level of circuit and
board design, cable design, choice of I C technologies etc. to meet the unit level EMC requirement.
Military equipment designers are required to
follow the guidelines given in military EMC
design hand books and to meet the unit level
EMC testing limits given in MIL STD 461/2/3 or
DEF STAN 59-41, for example.
The relationship between intersystem and
intrasystem EMC is shown in Figure 1.9. A
pictorial representation of a typical intersystem
EMI situation is given in Figure 1.10 showing
possible conducted and radiated coupling paths
between various systems. A similar representation,
but of intrasystem EMI, is given in Figure 1.11
using a transmitter with a case-mounted antenna
as an example.
1.3 Historical background
1.3.1 Early EMC problems
EMI problems and EMC solutions are not new.
Jolly [4], quoted by Braxton [5], tells of how at
around the turn of the century Gugielmo
Marconi had been contracted to build demonstration models of his new wireless telegraph sets
the
British,
French
and
American
for
governments. When he had installed several
equipments on board ships and at land sites, the
users complained that they could only operate
one station at a time. I t was therefore
discovered
by
acciden t
tha t
freq uency
management was important in communication
systems, as the spectrum from the crude transmi tters overlapped. Marconi had to return to the
installations and attempt to make them tunable
8
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
Followequipf1!ent specifications - ego MIL STD 461
SUBSYSTEM 2
SUBSYSTEM 1
EMI CONTROL
Figure 1.9
Follow system requirements - ego MIL STD 6051 D
IEC 801 FCC part 15/18
SUBSYSTEM n
COMPATIBILITY
WITH OTHER
KNOWN
SYSTEMS IN
OPERATIONAL
ENVIRONMENT
REGULATIONS
ON EMISSIONS
TO GENERAL
ENVIRONMENT
SUSCEPTIBILITY
TO GENERAL
CABLE-BORNE
INTERFERENCE
& TRANSI ENTS
IMMUNITY
TO
LIGHTNING
EFFECTS &
POSSIBLY
NEMP
Intersystem and intrasystem EMC
1.3.2 Early EMC problems with military
equipment
to avoid co-channel interference. This is
probably the first example of an EMC 'fix'
applied to an existing equipment. Many people
have followed Marconi's example in the
in tervening years.
While the International Special Committee on
Radio Interference (CISPR) has been tackling
-----
NATURAL & COSMIC ______________ -
-----
RADIO & ·STATIC· NOISE
/
RADAR & COMMUNICATIONS
TRANSMISSIONS FROM MOVING
LIGHTNING (DIRECT AND INDIRECT EFFECTS)
VE~~ ~
SYSTEM· 1
SYSTEM 2
Susceptibility to and
emissions of noise on
comms. lines (
Susceptibility to
and emission of
mains-borne
noise { ;
Susceptibility to and
emission of mains noise
POWER LINES
DISTURBANCES ON POWER-LINE
TELEPHONE LINES
Figure 1.10
Intersystem EMI
PICK-UP ON TELEPHONE LINES
NATURE AND ORIGINS OF ELECTROMAGNETIC COMPATIBILITY
POSSIBLE RF LEAKAGE FROM Tx ANTENNA
------------=M(AoLINC
INTO BOX via CONTROL PANEL
ANTENNA "'-
~
(Example of a transmilfer with a case mounted antenna)
\
FRONT
PANEL
CONTROLS
(Shield apertures if
possible)
SUBSYSTEM A
SUBSYSTEM B
Conducted EMI
TRANSMITIER......... OSCILLATOR
DOUBLER
CONTROL
STAGE
CIRCUITRY
Signal & Data
lines
POSSIBLE
CONDUCTED
NOISE
POWER SUPPLY
FILTER
EXTERNAL RADIATION
INDUCES CONDUCTED
EMI INTO MAINS CABLES
(DISTURBS POWER
SUPPLY REGULATION
WITHOUT FI LTERS )
Figure 1.11
9
MAINS POWER LEAD
RF CONTROLLED INTERNAL
TO SUBSYSTEM BY
SCREENING & FILTERING
~
INTERNAL UNWANTED
RADIATION PICKED UP
ON POWER & SIGNAL
CABLES
~
PA
POWER
LINE
~
~I
X:
SLOTS &
APERTURES
IN SUBSYSTEM
& SYSTEM CASES
POTENTIAL RF
LEAKAGE IN
CASES LEADS
TO PICK UP
INSIDE SYSTEM
ADEQUATE RF & SAFETY GROUNDS
Example oj'intrasystem EM!
the intersystem problems of interference to
broadcast receivers since 1934, the majority of
early interest in intrasystem EMC has been with
regard to military equipment. Early examples of
EMC problems aboard military aircraft have
been recorded [6, 7J and illustrate the problems
of the day, as follows.
1944 B29: Radiated and power cable conducted
noise
to
HF
and VHF communications
equipment.
1947 B50: EMI problems due to poor grounding
and bonding.
1950 B50, B47, C97: Problems with DC power bus
nOIse.
1954 B52: Interference from radar to communications equipment.
1958 B52: Problems with coupling between the
400 Hz power system and navigation and bomb
aiming equipment. In this case the problems were
so acute that production was stopped while cures
were found. Eventually modifications to both
cabling and equipment proved effective.
A similar history exists for naval equipment [8].
1939-45: Metric radar causes interference to HF
communications.
1945-55: During this period there was a great
increase in the use of servo equipment to control
guns for example. New 10 f.1V sensitivity
intercoms and tactical radio communications
were now using voice channels with microphones
distributed throughout the ship. New frequency
bands were used, sonar, radar and new navigational electronics were fitted. All these changes
made for a more complex use of the electromagnetic spectrum and resulted in increased interference between systems.
1955-65: The change from DC commutator power
generation to 440 V three-phase 60 Hz resulted in
an improvement in the ship board EM
environment, but at the same time the change
from lead clad cables to plastic sheathed ones
removed the natural screening offered by the
older type.
1965 onward: The introduction of semiconductor
technology greatly increased the number and
sophistication
of
electronic
eq uipments.
Introduction of digital computers and automatic
telegraphy all required greater vigilance in
spectrum management and the control of spurious
emissions from these devices.
1.3.3 The cost of EMC
Development programmes on early ICBMs such as
Atlas, Thor and Titan suffered delays owing to
EMC problems. The cost of EMC remedies and
programme delays ran into many millions of
dollars. A subsequent, more complex missile
development
included
an
EMC
control
programme which cost an estimated $3.5M but
resulted in minimal problems and no delays to the
project. This shows, on a grand scale, that when a
sensible EMC policy is adopted and implemented
10
A HANDBOOK FOR EMC'TESTING AND MEASUREMENT
early in product development considerable cost
benefit can result.
It is clear that failure to address EMC design
issues can result in major budget overspends and
programme delays. The cost of implementing an
EMC
control
programme
into
product
developme.nt is generally estimated at about 5%
of the development cost. With careful design and
choice of components and materials, the
additional cost element on each equipment sold
can often be small, and sometimes almost
negligible in the case of large production runs.
persuaded programme managers
over the
preceding ten years that the costs associated with
EMC engineering were affordable in order to
produce equipment which not only met formal
specifications, but also worked well in the field.
In the late 1980s and early 1990s engineers and
designers working in the civil electronics field
faced a similar situation [5, 11, 12] and the
commercial electronics business learned that good
EMC design is important if their products are to
compete successfully in national, regional and
global markets.
1.3.4 Serious EMI problems
1.4 Technical discil?lines and
knowledge areas wIthin EMC
As most EMC activity until the early 1980s was
associated with military hardware, it is to be
expected that problems would be associated with
this type of technology. One of the most
publicised incidents to military equipment in
which EMI was implicated was that which
occurred on the USS Forestall off Vietnam in
July, 1967. It was reported that RF energy from a
high powered ship's radar coupled into the firing
circuits of a aircraft-mounted missile rocket
motor, which ignited and fired the weapon into a
number of other armed aircraft on the carrier
flight deck. The resulting explosions and fire
killed 134 people and caused $72M of damage
not counting the 27 lost aircraft. More recently
(around 1980), interference to avionics from a
ground based transmitter was implicated in a
mili tary aircraft crash in Germany.
EMC activity in the nonmilitary world has
concentrated on the need to keep the electromagnetic spectrum free from interference to enable
comlTIunications systems to operate efficiently and
to minimise the upset caused to radio and
television broadcast reception.
The last 40 years have seen a dramatic increase
in the number of licensed radio services. In the
USA it is reported [9J that since 1950 the number
of broadcast stations has quadrupled to 11,000
radio and 1,400 TV stations. The FCC (Federal
Communications Commission) has also licensed
2.7 million mobile and fixed systems using 12
million transmitters [10].
With the widespread introduction of digital
computing
technology
and
microprocessor
controlled products into the commercial, industrial
and domestic environments in the early 1980s the
need for government agencies to act to control the
possible explosion in EMI was overwhelming.
By this time, EMC was firmly established in the
industries designing military electronic equipment
as an accepted part of the design and manufacturing/quality
process.
Many
early
EMC
engineers working on military products had
This section considers briefly the wide range of
technical skills that have a part to play in the
field of EMC. Each skill or knowledge area
discussed below is involved in solving EMC
problems. 1'he task of the product manager
involved with EMC is to blend these various skills
together to engineer robust EMC solutions into
the product at an affordable cost.
1.4.1 Electrical engineering
Electrical and electronic engineers are expected to
be knowledgeable in the following areas relevant
to EMC design and installation practice:
Analogue and digital circuit design
Semicond uctor device technology
Transien t suppression devices and circuits
Circui t board design
Component selection: operating limits and
reliability /cos t
EM aspects of mechanical design (propagation
through slots, holes, joints etc), grounding and
bonding impedances
Power generation, distribution and switching systems
Electrical safety and lightning protection filters
and surge arrestors
Grounding techniques, single/multipoint
Differential and common mode cable coupling
Transmission line theory
Screening theory a~d shielding design
Interface circuit design
Data bus and interface circuit design
Optoisolation techniques
Radiation from cables and slots in screens
Fourier transforms between freq uency and time
domains
Use of sophisticated RF test equipment
Principles of RF receivers and transmitters
Basic antenna theory
Radiowave propagation theory (near-field ,effects
being of particular interest)
NATURE AND ORIGINS OF ELECTROMAGNETIC COMPATIBILITY
11
1.4.2 Physics
1.4.4 Limited chemical knowledge
The physics of electromagnetic energy exchange
between RF currents and waves is very important
in understanding the complex processes that occur
in a real EMI situation. The manner in which RF
currents flow in and around the surfaces of
conducting and nonconducting complex structures
of the victim equipment determines to a large
extent the nature of an EMI problem. Developing
and implementing the means to contain, absorb or
divert such currents in a harmless way is the core
of good EMC design practice.
The physical equations derived by Maxwell
governing EM waves and their interaction with
matter form the basis for a real understanding of
EMI problems and their solutions. Such equations
can be solved generally using large 3D finite
element, finite difference, or boundary element
computer codes which can predict the current flow
patterns in a complex structure when illuminated
by an external electromagnetic wavefield.
The physics of EM wave propagation in both
the near and far fields must be considered by the
EMC engineer,
along with standing-wave
phenomena and the performance of radio
absorbent materials in large shielded testing
chambers if meaningful EMI measurements are to
be made and explained. Understanding how
EMC test antennas behave in the near field,
possibly amid multiple test chamber reflections, is
a difficult topic which represents a significant
challenge to the physicist involved in EMC
measurement.
Occasionally, good, apparently simple and costeffective solutions to an EMI problem are ruled
out because of concern about the chemistry of the
proposed design. Corrosion of RF gaskets due to
contact of dissimilar metals in damp, salt-laden or
corrosive atmospheres can be a real problem
which not only renders some EMI solutions void,
but can also result in serious damage to the
equipment cases or containers.
1.4.3 Mathematical modelling
Large projects that require EMC to be considered
at all levels of development often make use of
extensive computer models and the EMC designer
or manager should be familiar with the different
types used. These can include
(i)
(ii)
(iii)
Models of physical processes, such as RF
current distributions on structures due to
imposed EM field, wavefield to transmission
line coupling, lumped and distributed filter
performance in circuits with arbitrary
source and load impedances.
Models of intersystem and intrasystem
compatibility matrices to identify potential
EMI problems because of unwanted
frequency
matches,
noisy
culprit
equipments, oversensitive victims, or a high
level of coupling owing to the close
proximity of subsystems.
Programme management software that can
be used to monitor and control an extensive
EMC activity.
1.4.5 Systems engirleering
To be successful, EMC must be considered early,
when a contract to develop and supply electronic
equipment is being negotiated. Failure to do so
can result in incorrect bid pricing and an
eventual failure to comply with the contractual
EMC requirements. The customer requirements
must be interpreted and reflected in a system
EMC specification which is then apportioned to
each subsystem or element of the design. If these
tasks are carried ou tit is then possible to consider
a balanced hardening design of the system which
helps to ensure the most cost-effective route to electromagnetic compatibility.
1.4.6 Legal aspects of EMC
EMC requirements on products stem in part from
legal req uiremen ts by government agencies for
manufacturers
not
to
produce
electronic
equipment that will pollute the electromagnetic
spectrum. Failure to comply with such laws can
result in possible litigation by customers, other
suppliers, and of course, the official agencies.
Under the new EC harmonisation directive ECI
89/336 within Europe it becomes a criminal
offence to sell equipment which does not meet the
community EMC requirements as set out in the
harmonised or national (technically equivalent)
standards.
Corporate legal advice on EMC regulation is
beginning to be sought in the USA [10J and it is
inadvisable for EMC design or test engineers to
venture a direct opinion on the legal implications
of EMC technical matters. They should, however,
be in a position to advise management and
lawyers about the multitude of regulations and
standards which relate to EMC throughout the
world , particularly in those countries or trading
blocks into which their products are being sold.
1.4.7 Test laboratories
Often the formal proof of meeting an EMC
requirement is obtained from a test In an
accredited laboratory. This can be made within
12
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
the company that is developing the product or by
an outside specialist EMC test house. Clearly, the
test engineers must comprehend the EMC
standards and specifications, the philosophy
behind the testing approach, the detailed
technical methods used in testing and the quality
control
requirements
which
govern
test
procedures and test house management.
I t follows that it is also in the in teres ts of
designers and project managers to have a good
understanding of all these aspects of EM C testing
to be able to interact meaningfully with the test
engineers and understand the results which are
obtained. Providing such information is one of the
principIe aims of this book.
1.4.8 Quality assurance: total quality
management
EMC test engineers and managers of test houses
must be acutely aware of the need for discretion,
impartiality and q uali ty assurance in the conduct
of their business. The EMC facility manager is
required to hold delegated ,quality authority from
a senior company manager to ensure that the
laboratory is run in a manner which satisfies the
national
laboratory
accreditation
scheme
(NAMAS in the UK).
1.4.9 Practical skills
Effective EMC designers often have first-hand
practical engineering experience of equi pmen t
development and solving tricky RF problems with
relatively meagre resources. Experienced radio
amateurs tend to have a good understanding of
basic RF engineering, which incidentally, is being
taught less each year in university courses. Radio
hams often display a flair for EMC engineering,
offering cheap effective design solutions perhaps as
a result of using novel techniques.
The skills mentioned above are req uired by
individuals and teams in pursuing the goal of electromagnetic compatibility for electrical and
electronic products being developed in today's
commercial world of competitive costs and tight
timescales. Many of the issues and technical topics
touched on so far are amplified in the rest of this
book with the aim of giving the reader an appreciation of design practices and a good awareness
of EMC testing techniques.
1.5 Philosophy of EMC
Engineering of any kind can be viewed as the
creative process of defining, organising and
distilling out of a range of possible outcomes the
desired system performance. I t IS by the
application of consistent design constraints and
accurate manufacturing processes that electronic
equipmen ts with specific properties are produced.
EMC engineering is concerned with identifying,
understanding and managing the normally uncontrolled and often unexpected transfer of electromagnetic energy from device to device such that
the desired product performance goals are not
impaired. EMC engineering can therefore be
viewed as the application of an extra set of
controls or constraints to the design, manufacture,
installation, operation and maintenance of the
system in question, which ensures that the
equipment performs only those functions for which
it was designed, and does not respond to any
spurious signals resulting from EM interference.
This means that EMC engineers attempt to
design-out all spurious system responses, leaving
the product design engineers to design-in the
wanted performance. I t is the role of those
concerned with EMC to ensure that the second
broad element of system design, the 'not
engineering' is carried out cost-effectively in
conjunction with the usual design process if the
product is to avoid being compromised by EM!.
Perhaps the essential difference between the two
types of engineering is that the conventional
designer is concerned in great detail with only a
relatively !1arrow range of specific product related
issues whereas the EMC engineer, or designer
with responsibility for EMC, is concerned with all
possible external electromagnetic influences on
the proposed system.
Not all good electronics designers take to EM C
engineering: the subject seems to suit individuals
who enjoy lateral thinking and have a wide
interest in electronics, RF engineering and a
broad knowledge of the many skills outlined
earlier. However, most electronics designers can
become competent EMC practitioners with
appropriate training.
The next chapter looks in detail at the range of
EMC requirements and specifications used
around the world with which EMC managers,
designers and test engineers must be familiar.
This is the essential starting point from which to
develop an understanding of the technical factors
that are involved in EMC design and testing
aimed at meeting these specifications.
1.6 References
JACKSON, G.A.: 'The achievement of electromagnetic compatibility'. ERA report 90-0106, ERA
Technology, Leatherhead, Surrey, UK
2 DUFF, W.G.: 'Fundamentals of electromagnetic
compatibility'. Interference Control' Technologies,
Inc.
NATURE AND ORIGINS OF ELECT'ROMAGNETIC COMPATIBILITY
3 KEISER, B.: 'Principles of electromagnetic compatibility' (Artech House, 1987, 3rd edn.)
4 JOLLY, W.P.: 'Marconi' (Constable, London, 1972)
5 BRAXTON, T.E.: 'Selling EMC in a large organisation'. Proceedings of IEEE symposium on EMC,
1988, pp. 447-451
6 'Nature and characteristics of EM C'. USAF general
information document AFSC DH 1~4, section IB,
chap. 1
7 MORGAN, D.: 'An introduction to EMC'.
Presented at lEE fourth vacation school on RF
electrical measurernents, University of Lancaster,
july 1979
13
8 FIELD, j.G.C.: 'Electromagnetic compatibility in
warship design'. Proceedings of IERE symposium
on EMC, April 1978
9 FCC Public Notice 2519, April 1990
10 FCC 54th annual report, fiscal year 1988
11 STAGGS, D.M.: 'Ethics within the corporate
structure'. Proceedings of IEEE symposium on
EMC, 1990, pp. 526-528
12 HILLIARD, D.E., DESOTO, K. E. and
FELKERT, A.D.: 'Social and economic implications of EMC: A broadened perspective'.
Proceedings of IEEE symposium on EMC, 1990,
pp. 520-525
Chapter 2
EMC standards and specifications
2.1 The need for standards and
specifications
TC62 and industrial process and con trol
equipment was the responsibility of TC65.
2. 1. 1 Background
2.1.2 Contents of standards
As the use of electronic equipment grew and the
need to allocate and protect the electromagnetic
spectrum for communications became more
importan t, there arose the req uiremen t to develop
EMC regulations to ensure that an uncontrolled
situation did not develop. Governments sought
legislation through appropriate administrative
departments, giving force to sets of standards
which ensured that electromagnetic compatibili ty
was managed properly in the design and use of
certain categories of electronic equipment.
The style and content of standards were usually
characteristic of the nation which introduced
them, although in many cases they were based on
the, work of international bodies such as CISPR
(International Special Committee on Radio
Interference). This loosely co-ordinated national
approach led to problems in the commercial trade
of electronic equipment across national boundaries
both within Europe and with the USA.
The task of developing standards for the control
of EMC can be said to have begun in 1934 with
the formation of CISPR [1 J. The name CISPR is
derived directly from the French, Comite
International
Special
des
Perturbations
Radioelectriq ues, and was formed by several in ternational organisations coming together to institute
a joint comnlittee to specify measurement methods
and limits of radio frequency interference. Since
1950 CISPR has been a special committee under
the sponsorship of the IEC (International
Electrotechnical Committee) whose role is to issue
international standards.
CISPR has made considerable progress in
developing methods of measurement and limits to
deal with
interference
to communications
equipment. More recently, the appearance of
nonradio receiver interference phenomena led to
the involvement of the IEC. In 1982 it was
reported [2] that some 65 of the 200 committees
were concerned in part with problems of EMC.
For example, technical committee TC77 was
concerned with power distribution networks,
while TC18 produced the first EMC standard for
electrical installations in ships (IEC pub. 533).
Medical electronic equipment was covered by
The standards produced strive to ensure electromagnetic compatibility by requiring equipment
designers to consider the subject as part of the
design process from the earliest possible stage in
the development of the product concept. They
usually contain a section devoted to the definition
of relevant technical terms used in the document
and often specify the req uiremen ts for
planning and project management of EMC
test methods and specific test equipment
specified limits which must be met
specification for acceptable EMI measurement
receivers are also referred to in these standards.
As a good example of a well constructed standard
one may refer to UK defence standard DEF
STAN 59-41 [3J which is issued in five parts:
1
2
3
4
5
General req uiremen ts
Management and planning procedure
Technical requirements, test methods and limits
Open-site testing
Requirements for special EMC test equipment
(draft) .
EMC standards usually undergo a process of
evolution and updating to meet the developing
needs of industry and society. They are produced
after
extended
consultation
between
the
regulatory authority and the supplying industry
and other interested parties such as national
standards institutes. They contain a list of
definitions of words, phrases and technical terms
related to EMC and present carefully ordered
information with the aim of providing general
guidance [4J and sometimes specific instruction in
order to demonstrate compliance with the
associated specification limits. An EMC specification usually contains numerical details and
graphical representations of limits for measurable
parameters such as radiated field strength or
conducted interference current.
2.1.3 The need to meet EMC standards
With the development of the EC as a trading
entity, directives have been issued to harmonise
14
EMC STANDARDS AND SPECIFICATIONS
product standards in many fields. In the UK
demonstrating compliance with EMC standards
and related specifications for new and imported
electronic products is a legal req uiremen t from
1996 onward.
.
EMC specifications are also invoked within
commercial can tracts for the purchase of large
equipment and military systems. They can go
beyond. demonstrating compliance with the basic
legal requirements for EMC and contain
additional requirements that are specific to the
equipment and the environment in which it will
be operated. In this case, demonstration of
compliance is normally required by the purchaser.
Whether a manufacturer is satisfying the basic
legal requirement or a more involved contractual
one, the demonstration of compliance may be in
the form of a technical dossier and/or an EMC
test report. Such reports are normally produced
by an independent test house, or certain specifications permit the supplier to self certify the
equipment. In either case the measurements must
be made in strict accordance with the test
methods described in the specification and the test
laboratory will be operated within strict quality
guidelines and accredited by external q uali ty
authorities such as NAMAS [5].
2.2 Civil and tnilitary standards
2.2.1 Range of EMC standards in use
T'here are a large number of EMC standards and
associated specifications in use in the world today
covering an enormous variety of electrical, electromechanical and electronic equipment in various
industrialised nations. Table 2.1 [1] contains a list
of standards covering commercial equipment
which are, or have been, in force in a selection of
ind us trial coun tries. I t is inappropriate to discuss
them all in detail in a book on EMC testing but
some insights maybe gained into the nature of
these EMC standards and the relationships
between them by grouping them under the
headings military standards and civil standards,
as used in Europe, the USA, and other industrial
nations. This section explores the nature of
military and civil standards and specifications.
Subsequent sections examine specific illustrative
examples from the three groups.
2.2.2 Derivation of military standards
The substantial differences between military and
civil or commercial EMC standards and specifications are due to both equipment requirements
and the environments in which they operate [6].
Generally, mili tary req uiremen ts are more wide
15
ranging and stringent than commercial ones, and
thus more difficult and expensive to meet. As
military standards cover more aspects of electromagnetic compatibility over wider frequency
ranges than do commercial ones, many of the
examples of measurement techniques discussed
are taken from military standards.
The aim of one set of military EMC standards is
to ensure that mission success is not compromised
by poor intrasystem control of spurious electromagnetic energy. Additional standards control
intersystem EMC
/ ensure that individual
systems do not compromise each other's
performance in operation.
_
Standards are imposed by military procurement
authorities in the form of contractual conditions
which companies tendering to supply equipments
must meet. T'hey may insist on a contractor
demonstrating his EMC project management,
design, development and measurement capabilities prior to awarding a can tract.
In the fu ture, can tracts for large commercial
systems may also adopt _similar req uiremen ts as
the need to achieve good management of EMC
becomes more important.
The concept that underlies intrasystem EMC
standards is that if each identifiable electronics
box and each electronic subsystem meets the
standard then full system level EM C will be
achieved.
Writing specifications and defining test methods
for measuring spurious and unintended emissions
and
unwanted
responses is difficult and
documents are written not in terms of wanted
performance (as with most product design specifications) but by stating what may not be allowed
up to a given level.
A concept that is helpful in achieving system
level EMC by specifying box-level limits is that of
the source-victim margin. Each electronics box is
considered both as a source of electromagnetic
interference, either conducted or radiated and
also as a potential victim of such interference. See
Figure 2.1. The frequency, amplitude and
modulation characteristics of interference sources
and victims within each box are usually different.
A matrix may be drawn up showing each box in
a rank or file as a source and a victim. Any match
in terms of frequencies, levels and modulation
characteristics identifies the possibility of a system
level EMC failure. See Figure 2.2.
The key concept with these box-level military
EMC specifications is to set the limits of emissions
and susceptibilities such that there is a margin of
safety between them. If this margin is achieved it
is impossible for matches to be made in the cells
of the matrix in Figure 2.2 and system level
compatibility is ensured. Safety margins of 6dB
16
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
Table 2.1 Examples oj electromagnetic compatibility regulations Istandards oj various countries
Country
Ignition systems
CISPR
PUB 12
European norm
(72/245/EEC)
Australia
AS2557
Austria
Belgium
Household electric
applicances
Radio and
TV/video
PUB II
PUB 14
PUB 13
PUB 15
PUB 22
EN55011
EN55014
EN60555-213
EN55013
EN55020
EN55015
EN55022
AS2064/2279
AS I044/2279
ASI053
AS2643
OVE-F65
OVE-F61/62
OVE-F61/62
OVE-F64
OVE-F61/62
o V E- F61/62/55022
RCI960/74/76
RCj6.6.1966
RC/1978/1983
Royal Dec. 1960
RC1978f1983
EN55022
Canada
SOR 75-629
CSAI08-4
SOR/75629
CSA22-1/3/5
CSAC235
CSAC I08-5-4
CSACI08-5-2
SOR/75-629
SOR/83-352
CSACI08-5
Brazil
RF equipment
including ISM
Relevant CISPR PUBS
Fluorescent lamps
and luminaires
Solid state
controls
ASI054
IT & EDP
equipment
EN55022
also IEC/TCn standards
CSA22-4
VDI054
CSACI08-8
Czech.
CSN34-2875
CSN34-2865
CSN34-2860
CSN34-2870
CSN34-2850
Denmark
M04-j78
M03/83
M05689
M0416/NAHR3/2
M0396/NAHR4
M0416/ NAHR 5
NAHRI
M0416/568/396
Finland
PUB '1'35-65
PUB '1'33-86
PUB '1'33-86
T33-86/NAHR4
PUB '1'33-86
PUB '1'33
PUB '1'33-86
France
C91-103
C91-102
EN55011
NFC70-100
82/499/EEC
EN55014
EN50006
EN6055.1
C91-104
C91-110
EN60555
82/499/EEC
NFC91-100
82/500/EEC
EN55015
NFC91-100
NFC91-022
EN55022
Germany
72/245/EEC
VDE0879
VDEOl60
VDE0750
VDE0871
82/499/EEC
EN55014
EN55020
VDE0871
VDE0872
VDE0875
VDE0838
82/500/EEC
EN55015
VDE0875
VDE0875
VDE0871
VDE087.1/6/7
VDE0838
EN60555
Italy
72/245/EEC
CISPRII
EN55014
82/499/EC
CEIl 10-1
CEIn-1
EN50006
EN60555
CEIII0-3/4
EN60555
82/500/EEC
EN55015
CEIII0-2
EN55022
Japan
CISPRI2
JR'rC/MP'r
RERART65
JRTC73/74
EA&MCLAW
JRTC73/74/75
M P'f1970/71
EA&MCLAW
J R'!'C 71 /74/75
&82
CISPRI3
EA&MCLA\V
JR'!'C73/ 74/75
MPT1970/71
VCCI
CISPR22
Netherlands
72/24·5/EEC
NENI00I2
RCIOPREP
NENIOOII
EN55011
VDENI975
82/499/EEC
RC402/1984
EN55014
NEN-EN50006
EN60555
NENJOOl3
EN60555
82/500/EEC
RC401/1984
EN55015
RC/N.PNEP
CISPR22
EN55022
New Zealand
CISPR 12
NFCCOM
RFS4·9-1
RFS49-1
AS2279
BS5406
RFS49-1
CISPR13
CISPR15
ClSPR22
Norway
Regs for motor
vehicles 1969
43/6317
CISPRI2
NEMK0662/82
PUB. NO.
80POOS
CISPRII
NEMK031/83
EN55014
NEN67-76
EN50006
EN60555
NAHR4
NEMK0661/77
LET-NO.32/83
EN60555
NEMK031/83
EN55015
South Africa
R2862-1979
(CISPRI6)
R2862-1979
CISPRII
(CISPRI6)
R2862-1979
(CISPRI6)
R2862-1979
(CISPRI6)
SABS
(CISPRI6)
Spain
UNE20505
UNE20503
CISPR12
(CISPR16)
UNE20506
CISPRII
UNE20507
EN55014
RC2704/l982
UNE20511
EN60555
UNE20510
82/500/EEC
EN55015
United
Kingdom
BS833
(CISPRI6)
BS4809
BS6662
EN75-31
BS4941
BS4999
ERP (SERIES)
82/499/EEC
82/449/EEC
BS905
EN60555
82/500/EEC
BS5394
EN55015
BS800/1983
BS6345
USA
SAEJ551C
FCC Ptl8
FCC MP-5
MDS2010004
NEMA ICS-2
I EEE518-1982
MIL STD461/2
FCC Ptl5
ANSIC63-2
ANSIC63-4
NEMA WD2-1970
FCC Pt2
FCC Ptl5/C
FCC Pt15.J
FCC MD-4
EN55014
BS800
BS727
BS5406
EN60555
NEt\.1K031/83
(CISPRI4)
NEMK0665-168
NEMK0662/82
NEMK0661/n
NR33/83
NR32/83
EN55022
R2862-1979
SABS
(CISPR22)
EN55022
BS800 Pt3
BS6527
EN5S022
FCC Ptl5J
FCC MP-4
EMC STANDARDS AND SPECIFICATIONS
MULTIPLE INTERACTIONS TAKE PLACE
BETWEEN ALL UNITS
UNIT3
SOURCE 3 (f, I, m)
VICTIM (f, I, m)
tI
SUB-SYSTEMS or UNITS
(1 • n)
SYSTEM
Each unit is a source and a victim with
particular frequency level and modulation
characteristics
Figure 2.1
Intrasystem-source-victim
VICTIMS OF EMI
V1
S1
~
w
u.
S2
o
(f)
w
S3
V2
V3
V4
Vs
Vn
X
X
X
()
0:
::::>
o(f)
S4
X
X
85
X
Sn
Figure 2.2
Intrasystem interaction matrix
are used in the derivation of MIL STD 1541
(USAF) [7] for the limits for power and signal
cable interference levels, with a higher 20 dB
margin for ordnance circuits.
Established military specifications such as MIL
STD 461 C (USA) [8] are often tailored to the
specific requirements demanded by the procurement of a particular item of equipment, such as a
naval aircraft. Without the ability to tailor general
military EMC requirements it would be impossible
to achieve electromagnetic compatibility for a
unique system performing a specialist role in a
particular environment at an affordable cost.
In the case of commercial electronic equipment,
specifications cover particular categories of related
products. This approach does not involve
incurring the unjustifiable costs imposed by
meeting a general wide ranging specification.
VDE 0871 [9] is an example of a commercial
specification
concerned
only
with
ISM
(industrial, scientific and medical equipment).
17
2.2.3 Derivation of commercial standards
Regulations, standards and specifications relating
to commercial electronic equipment are aimed at
controlling pollution of the electromagnetic
spectrum and protecting radio communications.
The key intention is to limit the intersystem
radia ted or conducted interference emissions from
equipment to a level which does not cause
problems for radio and television reception.
An increasing number of commercial standards
address the susceptibility or immunity of
electronic equipment to electromagnetic threats.
However, the majority are concerned with the
control of unwanted emissions from
the
equipment. Commercial specifications are often
limited to conducted interference limits below
30 MHz and radiated limits only above 30 MHz
[6], since conduction along power or signal cables
is more likely at the lower frequencies and
radia tion is the more significant energy transport
mechanism at the higher frequencies.
The underlying assumption which determines
specification levels for commercial eq uipment is
that allowable emissions will be kept below the
strength which will degrade radio and television
reception based on practical receiving signal
levels. Assumptions are made as to the probable
distance separating a TV receiver and a radiating
equipment such as a personal computer in a
residential situation. This is taken to be between 3
and 30 m. I t is then possible to calculate the level
of an interfering signal at test distances of 3, 10
and 30 m for an acceptable received signal-tonoise ratio. See Figure 2.3. Interference limits at
the specified test distances are then issued
together with careful test methods designed to
determine whether an equipment meets them.
The characteristics of appropriate measurement
equipment are also specified, often based on
CISPR standards. These documents may be
referenced in the EMC regulations such as those
E
/
= 300 - 1000 ~ V1m
Building attenuation
/
(
---d----3, 10, 30 meters
E dB ~ Vim
p'(gure 2.3
-
Required SIN
( Signal to noise)
20 - 40dB
+
Building
attenuation
0- 10 dB
= Emission level limit
at distance
3 -30 meters
Regulatory model for radiated emissions from
electrical equipment
18
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
required by the FCC in the USA e.g. FCC part
15J
[10],
the
FTZ
(Fernmeldetechnische
Zentralamt or Central Telecommunications
Office) in Germany e.g. VDE 0871/0875 [11] and
in the UK by the DTI Radi.o Investigation
Service
[12,13] with specifications such as
BS4809, BS800, BS6527, etc.
2.2.4 Generation of CENELEC EMC
standards
This section briefly considers the process by which
the harmonised European Norm EMC standards
(discussed in Section 2.3) are produced. These
EN standards are now the most important for EC
manufacturers and importers of electrical and
electronic equipment. The European electrical
standards committee is known as CENELEC and
has been given a mandate by the EC to oversee
the harmonisation of national standards and to
prepare new ones when necessary. Technical
committee TC 11 0 has the responsibility for EMC
standards. EN standards are usually based on
existing CISPR documents which may be familiar
as they are similar to some British standards and
German VDE emissions regulations.
A simplified process of generating EN standards
by CENELEC is shown in Figure 2.4.
Government departments, trade associations and
other interested bodies can stimulate and
influence the appropriate British Standards
committee to represent their interests via the
national committee to CENELEC. Existing
standards may be used or modified to generate a
new draft EN standard. Once published for
comment, the interested parties will reflect their
views through the committee structure. A number
of revisions may occur before the technical details
and an agreed balance between the need for
EMC control and its economic impact on
industry and commerce is achieved.
Standards are continually developing and
evolving and EMC designers and test engineers
should keep themselves well informed of proposed
introductions of and changes to EN standards.
2.3 UK/European com.m.ercial
standards
2.3.1 UK standards relating to
commercial equipment
In the UK, EMC standards have been issued for
many years by BSI. Examples of widely used
EMC emission standards are listed in Table 2.2a
together
with
equivalent
EC
harmonised
European
Norm
(EN)
standards
where
a ppropriate.
Table 2.2a EMC emission standards
British
Standard
EC
equivalent
BS3GI00
pt 4 sec 2
BSG229
BS800
BS6527
EN55014
EN55022
BS905 pt 1 EN55013
EN55011
BS4809
BS5394
EN55015
BS5406
EN60555
BS833
BS1597
EN Documents
CISPR Standards
IEC, ECMA, CEPT
Applicabili ty
Equipment for use in
aircraft
Environmen t for aircraft
equipment
Household appliances
Information technology
equipment
Radio and TV receivers
Industrial, scientific and
medical
Fluorescent lamps and
lighting
Electrical supply
networks
Vehicles ignition systems
Interference suppression
in marine systems
There are also two widely used British Standards
which relate to the susceptibility or immunity of
commercial equipment to interfering signals.
These are given in Table 2.2b.
Other interested
boards
Figure 2.4
Process oj generating EN standards by
CENELEC
Table 2.2b EMC immunity standards
British
Standard
EC
equivalent
A pplicability
BS905 pt 2
BS6667
EN55020
HD481
Broadcast receivers
Industrial process
control
EMC STANDARDS AND SPECIFICATIONS
There are two other widely used UK standards
which contain immunity limits:
19
surface of a solid metal ground plane as in Figure
2.5 1 m from the antennas.
The technical details of antenna types, peak
detectors, narrow/broadbandwid ths and screened
rooms are all addressed and explained in the
appropriate chapters. As an example, the radiated
emission field-strength limits for this standard are
shown in Figure 2.6. (For an explanation of the
terms narrowband and broadband/referred to in
this Figure see Appendix 1.1.)
This BS3G 100 test may be contrasted with the
arrangemen ts for measuring radiated emissions
from data processing and electronic office
equipment as specified in BS6527/EN55022 where
the E UT is placed at 2. distance of 30 or 10m
(depending on whether the equipment is for
commercial or domestic use) from a measuring
antenna on an open field test site. See Figure 2.7
for a plan of the test site. No screening of ambient
signals is available on an open test site other than
that afforded perhaps by nearby hills. Such a
facility will preferably have been located in a
radio quiet environment but background/ambient
RF signals inevitably intrude on the measurement
which can slow down the testing while they are
identified and marked.
The specified measurement antenna to be used
in open range testing is a resonan t length
balanced dipole for frequencies above 80 MHz
and fixed at 80 MHz resonant length for
frequencies below 80 MHz. The need to manually
adjust the dipole at each test frequency is time
consuming and slows down the test. Broadband
an tennas such as the bow tie and log conical
spiral used in BS3G 100 are sometimes permitted
to speed up the measurement.
BS3G 100 pt. 4 sec. 2 'Equipment for use in
aircraft' also contains limits for equipment susceptibility.
NW0320 (National vVeights and Measures
Laboratory) is concerned with 'Weighing and
measuring equipment immunity to electrical
disturbances' and sets limits for electromagnetic
radiation, magnetic induction fields, electrostatic
discharge, power line transients and radiated
interference.
The characteristics of special test receivers which
are used to make interference measurements as
required by the emission standards are themselves
subject to another British Standard: BS 727 'Radio
interference
measurement
apparatus'.
This
standard is in line with the requirements of
CISPR publication 16.
2.3.2 Comparing tests
E.ach emission or immunity standard specifies
particular test methods and limits and in general
it is difficult to read across from one standard to
another. For example, the radiated emission
measurements in BS3G 100 are conducted with a
monopole, a bow tie (broadband dipole) and a
logarithmic conical spiral antenna connected to a
peak measuring receiver covering a frequency
range from 150 kHz to 1 GHz. All measurements
are made inside an RF damped screened chamber
to eliminate ambient noise, and the EUT
(eq uipment under test) carefully set out on the
Secondary power lines
to load NORM~LOR SIMULATED
Power
inputs
INPUT & OUTPUT CIRCUITS
Equipment
under test
~
Monopole antenna
14 kHz - 30 MHz
90 em
Figure 2.5
Log conical spiral antenna
200 MHz - 1 GHz
\
Metal plate
not less than
30 cm square
Typical radiated emission test corifiguration
Reproduced by permission of BSI
20
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
-g
1000: 61
;- 60
o
.0
~g 50
=.c 40
40
~
30
30
i
20
~
10
20 .:~
10 .8
o
"8
~
50
N
~
E
:>
::l.
co
co
'"C
'"C
1.0
10
FREQUENCY MHz
Figure 2.6
BS3G100 radiated emission limits
Reproduced by permission ofBSI
J o o e - - - - - - - major diameter = 2 F - - - - - - - - l
,.,....-
------T-----...
I
1
/
I
,,
...........
--.--
~
\
F=10-30m.---7E:
RECEIVING AERIAL
~,
2.3.3 European commercial standards
........ ,"'-
1
j(
I
\
-- ..........
minordiameter=V3F
///
-/-
)
EUT (equipment /
under test )
/
/
//
--- ----,...,
Boundary of area defined by an ellipse
Volume above earth to be free of reflecting objects
Figure 2.7
Plan view of open range radiation test site
Reproduced by permission of BSI
Other differences
between BS6527
and
BS3G 100 relate to the movement of the
measurement antenna to obtain maximum
received interference signal strength and the use
of a quasipeak detector in the receiver. The
Class A limits for the field strength of radiated spurious signals
in the frequency range 30 MHz to 1000 MHz
Test distance ( F )
Frequency range
m
MHz
Quasi-peak limits
dB
(~V/m)
30
30 to 230
30
30
230 to 1000
37
Class B limits for the field strength of radiated spurious signals
in the frequency range 30 MHz to 1000 MHz
Test distance ( F )
Frequency range
m
MHz
10
30 to 230
10
230 to 1000
Figure 2.8
Quasi-peak limits
dB
(~V/m)
30
37
BS6527 radiated emission limits for
open site testing
Reprod uced by permission of BS I
radiated emission field strength limits for BS6527
are shown in Figure 2.8.
A quick comparison of these two standards
clearly shows the difficulties that will be
encountered in trying to read across between
measurements made under different standards,
even within the same country. Great care should
be exercised in comparing standards, particularly
if the comparison is being made between UK and
other national standards for the purpose of
certifying compliance when exporting equipment
abroad. It is partly to overcome such problems
that the EC has pressed forward with a
programme of harmonisation of standards
including those relating to EMC.
In the early 1970s there was a wide diversity of
national regulations in Europe, some of which
were related to CISPR standards but many were
particular to a given country. This situation led
to problems with free trage in electronic goods
across national boundaries and gave rise to
various public purchasing and subsidy policies
which distorted fair competition [12].
With the signing of the Single European Act in
1985 governments were committed to a single
European market which was to be achieved
progressively by the end of December 1992. One
of the main tasks was to remove technical
barriers to free trade and this was to be achieved
by harmonising technical standards which
products must meet within all member countries.
E:rvIC standards came to be harmonised under
Directive 89j336jEEC of the 3rd May 1989 [14]
(amended by 91j263jEEC and 92j31jEEC).
These are complex and legalistic documents
containing many articles dealing with issues such
as definitions, applicability, release for sale,
recognition of special measures in member states,
relevant national EMC standards and declaration
of conformity. The scope of the directive includes
almost all electrical and electronic appliances,
equipment, systems and installations which are
brought into service within the community. The
directive has been implemented in UK law by the
Electromagnetic Compatibility Regulations 1992
(SI2372).
From October 1992 manufacturers of electrical
and electronic products governed by the
regulations have the choice of either following the
European Community regime, or continuing to
comply with the existing national 'legislation in
force' on the 30th June 1992 in the member states
in which the product is to be marketed [15].
Existing UK legislation on EMC is listed in
Appendix 1.2.
EMC STANDARDS AND SPECIFICATIONS
From 1st January 1996 most electrical and
electronic products made or sold in the UK
(including imports) must meet the requirements
of the EC directive on EMC. Failure to comply
will become a criminal offence and the product
will be prohibited from sale in the EC.
Most electrotechnical products are subject to
these regulations; there are however a number of
general and specific exclusions which are listed in
Appendix 1.2.
I t is envisaged that demonstration by
measurement that the equipment conforms to a
relevant harmonised EMC standard will be the
normal means of complying with the directive.
For some equipments it may be appropriate to
submit a 'technical file' or for radio communication
transmitting
apparatus
by
EC-type
examination.
There will be cases where a manufacturer
considers that it is inappropriate for equipment to
be assessed against such a standard. I t is possible
that no suitable standard exists. In such circumstances the assessment of compliance with the
directive shall be by means of the production of a
technical file and the involvement of a competent
technical body designated by the Department of
Trade and Industry, possibly a NAMAS
accredited EMC design/test house.
The directive permits the manufacturer to
demonstrate compliance by self certification in its
own test laboratories. Such facilities would
usually have EMC accreditation by a body
recognised for the certification of such laboratories. In the UK this would be a NAMAS
approval.
Listed in Table A1.3.1 in Appendix 1.3 are some
of the European EMC standards, their applicability and equivalent national or other
standards. Reference is also made to the closest
equivalent US standard. I t is, however,
dangerous to assume an exact read across to the
US FCC standards as many detailed differences
exist in test methods frequency ranges and limits.
I t will be evident from comparing the two parts
of the Table that there are no current equivalent
FCC EMC immunity standards in the USA,
though these migh t be introd uced for information
technology equipment.
Tables Al.3.2 and Al.3.3 of Appendix 1.3
contain lists in number order of EC EN
standards [16, 17] which have been referenced
in the official journal of the European
Communities and are therefore notified for use
in the self certification route to compliance with
the EC EMC directive.
Table A 1.3.4 [16] lists a number of proposed
product specific EMC standards on which
CENELEC is working (in 1993). The committee
21
aims to introduce these standards before the EC
EMC directive becomes mandatory in 1996.
The EMI limits and test methods recommended
by CISPR have been adopted as the basis for
many EN standards, European countries national
standards and EMC standards throughout the
world. Table A1.3.5 [1] in Appendix 1.3 lists the
relevant CISPR documents. CISPR standards
call for a quasipeak (QP) measurement of interference as this yields a result which is proportional to
the su bjective annoyance effect experienced by
radio broadcast listeners.
The characteristics of the quasipeak detector as
specified by CISPR publication 16 are given in
Table 2.3.
Table 2.3 Characteristics of CfSPR EMf meters
Frequency range
10 kHz150 kHz
Electrical charge
time constan t, ms
Electrical
discharge time
constan t, ms
6 dB detector
bandwidth, kHz
Meter time
constant, ms
Predetection
overload factor, dB
Postdetection
overload factor, dB
150 kHz- 30 MHz30 MHz
1 GHz
45
500
160
550
200
9
120
160
160
100
24
30
43.5
12
12
6
Similar specifications for EMI measurIng
receivers exist in the USA but they are not
identical to those of CISPR. The equivalent US
ANSI (American National Standards Institute)
C63.2 for measurement equipment contains a
value for electrical discharge time constant of the
q uasipeak detector in the freq uency range
150 kHz to 30 MHz of 600 ms rather than the
CISPR 160 ms.
2.3.4 German standards
Prior to the introduction of the EC EMC directive,
many designers and exporters of electrical
equipment paid particular attention to the
mandatory national requirements which existed in
West Germany. The VDE (German Institute of
Electrical Engineers) standards called up in the
national laws on EMC, promulgated by Vfg
(Decree Verfugung) and issued by BPM (Deutsche
22
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
Bundespost) are amongst the most stringent in the
world. Therefore demonstrating compliance with
the VDE limits would almost always assure
technical compliance in most other countries.
Table Al.4.1 [18] in Appendix 1.4 lists the
important Vfg decrees issued by the BPM and the
related VDE standards. In Germany the FTZ
(Central Telecommunications Office) have the
role of EMC adluinistration. This is comparable
with that of the FCC in the USA.
Because EMC standards are not yet fully
harmonised at an interna tional level there have
been many cases where a product which meets
the FCC limits for a particular category of
equipment has subsequently failed to meet the
appropriate VDE limits. This can be due to the
equipment designer failing to understand fully the
differences which exist, both in the- general
approach and in specific test methods between the
FCC and VDE standards. It is therefore
interesting to examine some of the similarities and
differences between these two important EMC
standards as the FCC rules apply throughout the
USA
and
the
VDE
specifications
have
contributed to the basis for the harmonised
European standards.
There is one major feature which is common to
both the FCC and VDE standards. Equipment is
divided into different classes depending partly on
operational use. For the US FCC part 15j
regulations, classes are defined as:
Class A: equipment which is used solely in
commercial environments where separations
between equipment will normally be tens of
metres and the professional eq uipmen t operators
will have some incentives to position their
equipments so as to cause the minimum interference to neighbours.
Class B: equipment which can be used in either a
commercial or a residential environment.
The applicable limits are for emission only and are
divided into conducted emissions below 30 MHz
and radiated emissions above 30 MHz. These
limits are given in Figure 2.9.
For VDE 0871/0875 regulations:
Class A: Normally for commercial equipment
requiring a test by VDE and individual permit
from FTZ/ZZF (RFI registration office).
Class B: General equipment for unrestricted distribution after self certification.
Class C: A special on site test provision for large
'one of a kind' installations.
Since the class A limits are less stringent than the
80
70~
I
Radiated emissions at 3 meters
-
FCC Class A
E
>
•
50~
FCC Class B -
::1.
to
'0
-
301I-
I
10
10
100
1000
FREQUENCY MHz
100
Narrowband conducted emissions
90
FCC Class A
----.r--
> 70
::1.
to
'0
FCC Class B
50
30
.01
0.1
1
10
100
FREQUENCY MHz
Figure 2.9
FCC limits for radiated and conducted
emzsszons
class B limits (see Figure 2. 10), the VD E is more
particular about the testing and accompanying
documentation for equipment tested to class A
standards. This is the opposite of the FCC
approach where class B products require FCC
authorisation and class A products are self
certified for compliance [18].
In Germany, equipment which is in the less
stringent class A had to be tested by the VDE
itself or at a VDE approved laboratory and
additional paperwork was submitted. Products
which fall within the more stringent class B can
be self certified. Manufacturers may therefore
choose to put their commercial eq uipment into
class Band suppress their emissions to meet the
lower levels to save test time and money by self
certification and bring products to the market in
the shortest possible time.
Manufacturers who sell both to the USA and
Europe, including Germany may opt to meet
the class A limits of the FCC (easier to test) for
the USA market and VDE 0871 class B limits
which are easier to test and market in Europe.
Lohbeck [18] gives an excellent precis of the
main differences between FCC part 15j and the
FTZ (VDE 0871 and 0875) standards. See Table
Al.4.2 in Appendix 1.4.
EMC STANDARDS AND SPECIFICATIONS
100
r__---__
---~r__---......__---_
Narrowband conducted emissions
80
""
>
::l
CD
"0
"",
._----
---,
60
VDE Class A
VDE Class B
40
0.01
0.1
1
100
10
FREQUENCY MHz
80
_--------r--------_
Electric field
VDE Class A
60
E
>
et
40
"0
VDE Class B
20
10
100
1000
FREQUENCY MHz
wI"--
(l')LO
00
, '
g~
00
120-....~---
103.5
100
91.5
80
~
0'~140625
Z~A~25
109375
06375
63.5
60
::l 51.5
CD
"0
40
41
± 001
.
078125
0625
20
.01
0.1
1.0
10
30
FREQUENCY MHz
Figure 2.10
VDE 0871 conducted and radiated limits
2.4 US commercial standards
2.4.1 US organisations involved with
EMC
FCC, the Federal Communications Commission, is
responsible for spectrum allocations outside the
government sector.
NTIA, the National Telecommunications and
Information Agency, has a committee named
IRAC
(Interdepartmental
Radio
Advisory
Committee) which is responsible for spectrum
allocations within the federal government sector.
NASA is concerned with the EMC aspects of
23
equipment and systems for use in aerospace
vehicles.
NCMDRH, the National Center for Medical
Devices and Radiological Health, is concerned
with the safety aspects of both ionIsIng and
nonionising radiation produced by electrical and
electronic products.
NBS is renamed the National Institute of Science
and Technology
(NIS1-'),
concerned
with
metrology
in
general,
of which
EMC
measurement is a part.
NVLAP, the National Voluntary Laboratory
Accreditation Programme, is administered by
NIST and provides confidence that EMC testing
carried out by laboratories in the USA within
the progralume are to the desired q uali ty
standard.
Industrial organisations concerned with EMC
standards and measurement within the US
include:
EIA, the Electronics Industries Association, IS
concerned with equipment EMI.
IEEE is concerned with EMC standards.
SAE, the Society of Automotive Engineers, plays a
special role in respect of both air and land vehicle
EMC. For example, SAE Practice ARP-937
relates to jet engine EMI and applies to electrical
systems
and
accessories,
ignition
systems,
actuators, fuel con troIs, solenoids, servo con trol,
electrical alternators, etc. This SAE document
covers conducted and radiated emission and
conducted susceptibility requirements.
R TCA, the Radio Technical Commission for
Aeronautics, issues documents on the airborne
equipment environment, which includes sections
on EMC and lightning.
ANSI, the American National Standards Institute,
is concerned with measurement techniques
including those for EMC.
2.4.2 FCC requirements
The involvement of the FCC in the realm of EMC
began in 1934 when the Communications Act of
that year gave the FCC the authority to impose
rules and regulations on industrial, commercial
and consumer devices which could radiate electromagnetic energy. The significant parts of the rules
and regulations with regard to EMC are set out
in title 47, parts 15, 18 and 68 of the US Code of
Federal Regulation (also known as FCC docket
20780). A list of the parts relevant to EMC is
given in Table A1.5.1 of Appendix 1.5.
FCC part 15j covers any device that intentionally generates and uses electrical energy in excess
of 9 kHz or 9,000 pulses per second for
24
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
computation, control, operations, transformations,
recording, filing, sorting, storage, retrieval or
transfer of data. The rules encompass computing
device peripherals but exclude transmitters and
receivers and devices covered by other FCC
regulations, computing devices used in transportation vehicles [19J, and control or power systems
used in public utilities and a range of other ISM
and household equipment that are covered by
other regulations.
FCC part 15 regulations address only emissions;
however, the laws provide for susceptibility
testing as well. The FCC has chosen not to
mandate susceptibility or immunity limits for
commercial equipment as it prefers to leave this
responsibility to the manufacturer whom it
supposes to have a self interest in the compatibility of its equipment with the EM environment
in which it is to be operated.
The FCC has five administrative arrangements
for dealing with equipment that emits nonionising
radiation
including
both
intended
and
unintended emissions:
(i)
(ii)
(iii)
(iv)
(v)
Type acceptance is based on information
and test data supplied by the manufacturer
or licensee to the FCC, which may then
choose to test the item.
Type approval is granted when an
equipment has passed the specified FCC
test. Tests are carried out by the FCC.
Certification is similar to type acceptance,
however, no licence is held by the user.
Verification, when the FCC carries out spot
checks to ensure that the manufacturer's
self testing has been suitably carried out.
Notification. In this procedure the FCC may
not require detailed data to accompany an
application.
The applicable arrangement will depend on the
nature of the equipment for which EMC
clearance is being sought.
2.4.3 Other US commercial standards
A list of some examples of the standards prepared
by bodies other than the FCC is given in
Table 2.5.2 of Appendix 2.5.
2.5 Cornm.ercial EMC standards in
Japan and Canada
These two countries are examples of important
producers and markets for electronic products
and both have laws or voluntary regulations
governing EMC.
2.5.1 Japanese EMC standards
Japan has had the Electrical Appliance and
Material Control Law for many years which is
concerned with regulating EMI from household
electrical appliances, electrical tools, fluorescent
lamps, radio and TV receivers. The radio
equipment regulations, article 65, is concerned
with radio frequency equipment including ISM.
The measurement equipment and techniques are
defined by the JRTC (Japanese Radio Technical
Council)
of the Ministry of Posts and
Telecommunications (MPT).
In 1985 the Japanese Electronic Industry
Development Association, the Japan Business
Machine Makers Association, the Electronic
Industries Association of Japan and the
Communications Industry Association of Japan
came together at the request of the MPT to form
the Voluntary Control Council for Interference
by Data Processing Machines and Electronic
Office Machines, known as the VeeI [24]. The
goal of the VCCI is
'To take voluntary control measures against
electronic interference from data processing
eq uipment and electronic office machines, and
thereby contribute to the development of a
socially beneficial and responsible state- of affairs
in the realm of electronic data processing
equipment inJapan'.
Membership is not limited to Japanese companies
and is open to foreign organisations. Some
overseas manufacturers of electronic equipment
have found membership of, and compliance with,
the VCCI beneficial in competing in the Japanese
market place. Members must test the product for
conformance and submit a report in Japanese to
VCCI before placing the equipment on sale.
When the report is registered a certificate of
acceptance is awarded to the company for that
product.
There are two classes of equipment specified in
the VCCI standards:
Class 1: information technology equipment (ITE)
used in industrial and commercial applications
Class 2: ITE used in residential situations.
The limits applied to the two classes for equipment
manufactured after December 1989 are equal to
those specified in CISPR 22 [25 J. The VCCI
limits for radiated emissions are given in Figure
2.11 and those for conducted emissions in Figure
2.12. These VCCI limits are similar to the FCC
and VDE limits but there are differences in
frequency coverage, test methods and the
arrangement of the equipment under test. A
limi ted comparison of the test methods set out in
EMC STANDARDS AND SPECIFICATIONS
80
I
Radiated emissions at 3 meters
~
E
60
>
::t
CD
'U
-
-
VCCI Class 1 _
-
VCCI Class 2. _
40
-
20
:~
-
-
I
1000
100
10
FREQUENCY MHz
VCC! radiated emission limits
Figure 2.11
100
Narrowband conducted emissions
80
VCCI Class 1 Quasi-peak limits
>
VCCI Class 1 Mean limits
::t
CD
'U
60
40
1
0.1
10
100
FREQUENCY MHz
1 0 0 - - - - - - - - - - - - . . - - - - - -..........
Narrowband conducted emissions
80
>
'-
::t
CD
'U
60
VCCI Class 2 Quasi-peak limits
"'-.
,
I
......-----V-C~C..I Class 2 Mean limits
40
0.1
1
10
100
FREQUENCY MHz
Figure 2.12
VCC! conducted emission limits
the three standards has been made by Hoolihan
et al. [24J, see Table A1.6.1 of Appendix 1.6.
25
Communications announced that they intended
to regulate radio frequency electromagnetic noise
emissions from digital electronic devices. All such
devices manufactured or imported after 31st
January 1989 must have been tested and shown
to comply with the new regulations [26J and
carry an identifying mark to that effect.
Under these new regulations products are
divided into two groups: class A, industrial and
class B, residential. The class B limits are set at a
lower level of tolerable emissions than class A and
in this respect are the same as the FCC and VDE
standards. As in the USA there are some products
which contain digital devices which are exempt
from the regulations. For Canada these include
Transportation vehicles
Public utility or industrial plant
Test equipment in industrial, medical or
commercial environments
Certain motor driven domestic appliances
Some medical equipment and monitors
Some central office telephone equipment
Systems using radio transmitters and receivers.
The Canadian EMC regulations are referred to by
the publication number SOR/88-475 [27]. The
associated testing procedures are given in CSA
standard C 108.8-M 1983 [28J. The testing
procedure is similar to that defined by the FCC,
but it is not identical [29J. The Canadian
Department of Communications (DOC) makes
the important stipulation that a product tested
and shown to be compliant with the FCC
regulations need not be retested. The FCC report
will be accepted as proof of compliance provided
that a note is attached indicating that the results
are considered to be satisfactory proof of
compliance with the Canadian regulations.
Compliance with the DOC regulations will be
verified by the Canadian authorities if a
complaint of interference caused by the product is
received, investigated and subsequently confirmed.
The applicable limits for radiated emissions
30 MHz-1 GHz and the conducted interference
limits from 450 kHz-30 MHz are given in Table
A1.6.2 of Appendix 1.6.
2.6 Product safety
2.5.2 Canadian EMC standards
Canada has legal requirements for EMC covering
vehicle
ignition
systems,
radio
frequency
equipment including ISM and TV receivers
under regulation SOR/75-629 1975. Voluntary
compliance to CSAC108.5 standard has been
sought for products such as household electrical
appliances and fluorescent lamps. In January
1987
the
Canadian
Department
of
2.6.1 Safety of electrical devices
Electrical product safety and the safety of humans
and ordnance devices when exposed to high
power electromagnetic radiation is not the
primary subject of this book. However, these
topics are related to EMC, and often both safety
and EMC specifications must be met simultaneously
in
a
single
equipment
design.
26
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
Occasionally, the design that gives the best EMC
resul ts might be in contraven tion of the electrical
safety rules. This can occur, for example, when
considering the optimum grounding or earthing
policy for an equipment where a safety earth can
act as an effective radiating antenna.
2.6.2 Product safety
From the manufacturer's point of view there are a
number of legal and commercial advantages to be
gained by designing and testing equipment to
meet the widest range of electrical and electromagnetic safety regulations which exist world wide. He
can thereby ensure that his equipment is operable
and reliable within the boundaries of recognised
minimum safety standards [30J. Safety agency
periodic audits of approved products will also
encourage manufacturers to maintain their
product safety quality control during production.
Probably the most important benefit to be
gained by meeting recognised safety standards is
the almost certainly reduced liability judgements
that may be made against a manufacturer in the
event of safety litigation. For example, in
Germany when equipment carries a separate
VDE or TUV [31J laboratory safety mark (see
Figure 2.13), then liability of the manufacturer in
the German courts is minimal. When the
approving agency mark is applied to the product,
this places the burden of proof on the end user
not the manufacturer.
is human. There are diverse opinions with regard
to safe levels of exposure. In the West the generally
accepted criteria for exposure to CW irradiation
are based on the thermal effects genera ted wi thin
the body by the absorption of RF energy. The
approach in the former USSR to human exposure
seems to be based on the effects of RF energy on
the central nervous system, which are stated to
occur at between one to two orders of magnitude
lower power density than for thermal effects [32].
There are little data available in any country on
the effects of intense short pulses or on chronic
exposure at low levels. Concerns are beginning to
be expressed about safe levels of low frequency
magnetic fields at power line frequencies [33]. l'he
biological effects of exposure to electromagnetic
fields are likely to become a significant technical,
legal and social issue in the 1990s. In a modern
ind ustrial society many millions of people may
rou tinely be exposed to RF radiation of some kind
during their occupation. Typical categories of
workers are listed in Table 2.4 [34]. Table A1.7.2 of
Table 2.4 Industries involving use oj electromagnetic
energy
Sector
Application
Industrial
Food preparation by
mIcrowaves
India rubber processing
Adhesive processing
Heating or fusion of metal and
crystals
Medical
Diathermy
Magnetic resonance imaging
Computer imaging of x-rays
Ultrasound procedures
H ypothermy-sensi tising
malignant tumours
Military
In the USA, the Underwriters Laboratories and
in Canada the Canadian Standards Association are
the recognised agencies for safety testing of
electrical products. Typical national and international electrical product safety standards are given
in 1'able A1.7.1 of Appendix 1.7 and EMC
engineers should be familiar with these technical
requirements as design measures which ensure
product safety will always override those for electromagnetic compatibility if a choice has to be made.
Communications
Radio navigation
Aviation
Preparation of precooked
foods
Weapons guidance and
triggering devices
Radar systems
Radio communications
Research and
scientific
applications
Food processing
Plastics
Chemical applications
Metal stress tests
2.6.3 Radiation hazards to humans
Communications
Radio stations
Portable transmitters
Satellite hookups
Figure 2.13
Product safety mark
A special case of electromagnetic compatibility
exists when the potential receptor or victim system
EMC STANDARDS AND SPECIFICATIONS
1Q3------IUK MoD(1982)
r-'-..- -..\
l:fSARMV"1L-------..,
I STANAG 2345
:
I
STANDARDI (WORKERS AND
I POPULATION)
NEW(1982~ANSI
1()2 US AIR
:
FOR~~~.~.~.~~~.~.~. ~.~11
E
~
E
~
T -\
NIOSH
101 STANDARDS
(WORKERS)
~
~\.
"'~
ffi
0.
"
10-1
/
.... /
-I , r -
\\..... _ ..... _ ..... _ ..... /'....
\ NRPB(1989) / /
~
~
/'7
ART. 5
\.
1 INIRC (1988>"
I US NAVY
llj--:r;;EvIOUS ANSI STANDARD
:' .....tl'J:.::lbln.:r!:._._._i::n:.lI:'l:'l:l'\I.lII'I:Ill'I:_ _ .::nt.
EEC
\.
~
HUMAN BODY
RESONANCE REGION
'-- __ -0/
~~--'
SOVI ET WORKER
STANDARD
UK NRPB (1986)
PUBLIC ACCESS
5 HOURS/DAY
10-2
10·3 1--_ _--'0.1
L..---'-_........_ L - - - - L_ _----'
10
100
1GHz
100Hz
FREQUENCY MHz
Figure 2.14
Comparison of electromagnetic wave
exposure standards
Appendix 1.7.7 contains examples of standards
regulating human exposure to RF energy.
A comparison of the limits contained wi thin
some of these standards is given in Figure 2.14
including those proposed by INIRC (1988). Safe
levels of exposure were recommended by the
NRPB (1986) in a consultative document which
was revised in 1988 and issued as NRPB-GS 11.
The recommended reference levels are gIven In
Table A1.7.3 of Appendix 1.7.
2.6.4 Hazards of electromagnetic
radiation to ordnance
The history ofRF ignition hazards goes back to the
First World War when experiments showed that
cotton bales could be ignited by RF power
induced into the restraining metal bands [41]. The
high-power RF hazard has long been recognised
in the USA and studied by a variety of agencies
[42-45]. Work in the UK by Excell [46] assisted in
updating BS4992 (1974) 'Guide to protection
against ignition and detonation initiated by radio
frequency radiation'. BS4992 has now been
superseded by BS6657 'Prevention of inadvertent
initiation of EEDs (electro explosive devices) by
RF
radiation',
and
BS6656
'Flammable
atmospheres and RF radiation'. In BS6657 a
comprehensive list is given of minimum safe
distance for EEDs from transmitters employing
various powers, polarisations and modulation
27
types. In Germany, the standard for RF ignition
hazards is VDE 0848 (DIN57848 issued by the
German standards institute). There is also an international standard issued as IEC 79-2, 'Electrical
apparatus for explosive gas atmospheres'.
The RF ignition of ordnance (HERO) is a
safety-cri tical feature of military eq ui pmen t
which con tains electrically triggered ini tia tors
(EEDs). They may be used to activate switches,
separation fastenings and set off explosives or
rocket motors. Accidental ignition is clearly a
serious issue bu t if the explosive mixture is
heated and not detonated by currents induced
into the firing fuse in the EED this can render
the explosive chemicals unresponsive to a
subseq uent real firing pulse. This is called
d udding and is also a concern for the safe
operation of the system.
In the UK, the pertinent regulations posted as
Ordnance Board (OB) Proc.41273 [47], are now
superseded by OB Proc.42413 March 1986. EMC
engineers are often called on to design and test
EED circuits as part of the wider system and they
should be familiar with the appropriate regulations.
2.7 ESD and transients
2.7.1 ESD (electrostatic discharge)
With the conjunction of the spread of digital
instrumentation, process control equipment and
general information technology in to office
buildings and industrial plants fitted with
synthetic materials and h umidi ty controlled air
conditioning, a particular type of transient EMI
became a problem [48]. Digital equipment is
inherently sensitive to short high-level widebandwidth voltage transients caused by the
discharge of electrostatic energy which can easily
build up on people, chairs and tables etc. in
environments with abundant insulators (plastics
and manmade fibres). These transients can cause
digital data disruption, microprocessors to change
function and even to lock up. ESD and fast
transients are becoming a more important part of
EMC as the need increases to understand and
con trol this phenomenon across a wide range of
equipment.
The measurement procedure defined in BS6667
Part 2 (and in IEC80 1 Part 2) recommends test
levels of between 2 and 15 kV using a specially
designed spark discharge probe. See Figure 2.15.
The in ten tion is to simula te the discharge of
static electricity built up on an equipment
operator into sensitive circuits via conducting
metalwork.
28
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
ESD GENERATOR
PROBE
I
I
MAINS OUTLET
WITH EARTH
TERMINAL ~
PROTECTIVE
CONDUCTOR
/
EARTH REFERENCE PLANE
PLANE
CLAMPING DEVICE
Figure 2.15
Typical ESD test
Reproduced by permission of' BSI
2.7.2 Transients and power line
disturbances
Immunity to fast transients due to switching on
mains supplies is also increasingly important with
the widespread introd uction of semiconductors
and digital microprocessors into domestic,
commercial and industrial equipment. It is only
relatively recently that international agreement
has been obtained with regard to suitable test
methods and limits. The methods call for
transients to be induced into the equipment mains
leads directly or via a distributed capacitance.
The characteristics of the transients which must
be injected are given in IEC 801 part 4 and have
a risetime of only 5 ns. The regulation specifies
Risetime
Pulse length
Burst duration
Burst period
Rep. frequency
(within burst)
5 ns ± 30%
50ns
15 ms
300ms
5kHz
(for amplitude up to 1 kV)
2.5 kHz (above 2 kV)
for military electronic equipment have been
developed around them. Because of this, many of
the examples of the wide range of EMC
measurement techniques discussed in this book
are described with reference to these standards.
Some of the EMC tests included in these
standards are not yet required for commercial
electronic equipment. With the inevitable proliferation of equipment in the future, and the
consequent increase in the importance of EMC,
adaptations of some of these tests which currently
apply only to military systems may become
relevant to commercial equipment.
MIL STD 461/2/3 documents and their
successors are issued by the US Department of
Defence and are now used around the world.
MIL STD 461 A entitled 'Electromagnetic interference
characteristics
requirements
for
equipment' and first issued in August 1968 aims
to ensure that interference control is considered
and incorporated into the design of equipment
and subsystems. I t also provides a basis for
evaluating the electromagnetic compatibility of
these equipments and subsystems when operated
in a complex electromagnetic environment. The
standard is concerned with both radiated and
conducted emissions and susceptibility of an
equipment as illustrated in Figure 2.16.
The associated standards are MIL STD 462,
'Measurement of electromagnetic interference characteristics', first issued in July 1967, and MIL STD
463, 'Definitions and systems of units for electromagnetic interference technology'. These can be applied
to single or multiservice procurements and are
called up in the equipment specification and
contract. Compliance with the requirements of
these standards does not guarantee that the
equipment will not suffer from any EMC problems,
but it should ensure that they are minimised
without incurring excessive costs for over protection.
There are also standards which specify the
limitations of disturbances caused in electricity
supply networks
by domestic and
other
equipment; BS 5406 (1988) or IEC 555 are
examples. The practising EMC engineer must be
aware of these power line transients and ESD
specifications and may be called on to design and
test systems to which they are applicable.
emIssIon
2.8 US tnilitary EMC standards
I.
¥ h
INTERCONNECTING
CABLE
POWER CABLE
2.8.1 MIL STD 461/462/463
These standards are among the most formal,
technically comprehensive and widely used of all
EMC standards. Many other tests, particularly
"7
Conducted
susceptibilIty
f-'igure 2.16
Unit- or box-level en7ission and
susceptibility testing (MIL SYD 461)
Reprod uced by permission of' ICT Inc.
EMC STANDARDS AND SPECIFICATIONS
MIL-STD 461A
1st August 1968
NOTICE 1 CORRECTIONS
2nd February 1969
NOTICE 2 (AIR FORCE)
20th March 1969
NOTICE 3 (AIR FORCE)
1st May 1970
NOTICE 4 ( ARMY)
9th February 1971
NOTICE 5
( MOBILE ELECTRIC POWER)
6th March 1973
NOTICE 6
( CORRECTIONS TO NOTICES)
3rd July 1973
Figure 2.17
MIL SYD 461A and revision notices
Reproduced by permission or ICI' Inc.
MIL STD 461A has been the subject of many
revisions and amendments over the years and this
is illustrated in Figure 2.17. Similarly, revisions
have taken place to the testing methods and limits
in MIL STD 462. See Figure 2.18. Many of the
amendments have been concerned with procuremen ts for a single service (army, navy or airforce).
The test req uirements are organised logically
and can be represented as shown in Figure 2.19 in
the form of a flow chart or tree showing the
successive subdivisions into emissions and susceptibility, then conducted and radiated mechanisms
for each, and so on. Not all of these tests need be
performed on all equipment which falls within the
MILSTD462
31st July 1967
NOTICE 1 CORRECTIONS
1st August 1968
NOTICE 2 ( AIRFORCE )
1st May 1970
NOTICE 3 (ARMY)
9th February 1971
Figure 2.18
MIL SYD 462 and notices
Reproduced by permission or rCT Inc.
29
general regulations. Equipments are grouped into
classes and further divided into subclasses. See
Table A1.8.1 of Appendix 1.8. Only certain tests
are carried out within a given class as illustrated
in Table A1.8.2 of Appendix 1.8.
In 1980 a major revision to MIL STD 461A was
issued as MIL STD 461B. It was the outcome ofa
significant change in the philosophy which
underpinned the intentions of the regulations. All
equipment purchased for the US military was
required to meet EMC specifications derived from
the equipment type or class and the intended
installation and criticality of the equipment to
'mission success'. Thus MIL STD 46IB is
sectioned into parts 1 to 10 which correspond to
the types of installations in which the equipment
will be used. See Figure 2.20. The relationship
between the equipment classes and subclasses to
the numbered sections or parts of 46IB is shown
in Table A1.8.3 of Appendix 1.8.
The inclusion of the impact of installation and
mission aspects in addition to the equipment
classes is a further attempt to ensure enhanced
operational electromagnetic compatibility, but
again at a reasonable cost, by tailoring the
requirement for only certain tests as appropriate.
In some cases, further tailoring will be necessary
for specific missions such as navy carrier aircraft
[49] which have to operate in close proximity to
powerful radar and satcom antennas. In such
situations field strengths for the RS03 test may
need to be increased to 200 V 1m or more to
ensure operational EMC.
There are many differences between MIL STD
461A and 461B which are too numerous to be
described in detail in this book. However, some of
the major changes to tests are listed in short form
in Table A1.8.4 of Appendix 1.8. Some of the
tests introduced into MIL STD 46IB are only
applicable to procurements for particular services
and readers should consult the Standard for
further detail.
A second upgrade and revision of this series of
military standards arose in 1986 with the introduction of MIL STD 461C. The new standard
retains the same format as 46IB and introduces a
number of modifications [50]. The most
important addition is that concerned with tests
designed
to
ensure
survival
of military
equipments against EMP (electromagnetic pulse).
The following tests have been added and are
applicable to installations listed in parts 2, 4, 5
and 6 of the document:
CSIO: pulse injection onto equipment pins
CS 11: pulse injection onto interconnecting cables
The characteristics of the damped sinusoid
to be injected are given in Figure 2.21.
30
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
MIL STO 461
Specification test requirements
RS 01 30 Hz - 30 kHz
RS 02 Magnetic induction
Electric and
electromagnetic
Electric and
electromagnetic
RE 02 14 kHz - 10 GHz
RE 03 10 kHz - 40 GHz
spurious & harmonic
RE 05 150 kHz - 1 GHz
vehicles
~
CE 02 30 Hz - 20 kHz
CE 04 20 kHz - 50 MHz
CE 05 30 Hz - 50 MHz
RS 03 10 kHz - 10 GHz
RS 04 10 kHz - 30 MHz
(parallel plate)
engines
RE0614kHz-1 GHz
overhead power lines
Transmitter: key up
Transmitter: key down
Receiver: LO leakage
Figure 2.19
MIL STD 461 test specifications
Figure 2.20 MIL STD 461B
and 462 (notices 4 and 5)
MIL STD 461 B
1st April 1980
MIL STD 462
31 st July 1967
PART 1 - GENERAL
NOTICE 1 - CORRECTIONS
1st August 1968
PART 3 - SPACECRAFT & GSE
or ICT Inc.
NOTICE 2 - ( AIR FORCE)
1st May 1970
NOTICE 3 - ( ARMY)
9th February 1971
PART 4 - GROUND FACILITIES
NOTICE 4 - INTERIM NEMP
(CS 09 TEST) 1sf April 1980 (Navy)
PART 5 - SURFACE SHIPS
NOTICE 5 - INTERIM NEMP
(CS 10 & RS 05) 5th January 1983 (Navy)
PART 6 - SUBMARINES
PART 7 - NON-CRITICAL GROUND AREA
PART 8 - TACTICAL & SPACE VEHICLES
PART 9 - ELECTRIC POWER
or ICT Inc.
CS 03 30 Hz - 10 GHz
Intermodulation
CS 04 30 Hz - 10 GHz
Signal rejection
CS 05 30 Hz - 10 GHz
Cross modulation
CS 07 Squelch circuit
CS 0830 Hz -100Hz
(signal rejection)
Reprod uced by permission
PART 2 - AIRCRAFT & GSE
Reprod uced by permission
CE 01 30 Hz - 20 kHz
CE 03 20 kHz - 50 MHz
CE 05 30 Hz - 50 MHz
PART 10 - COMMERCIAL
EMC STANDARDS AND SPECIFICATIONS
100
I mtlX
nnnII n
1\
A
_
!~nME
~ 10
E
31
electrical
and
electromagnetic
in terference
phenomena. The aim of the standard is to ensure
a compatible total system under operational
condi tions and therefore is concerned with
II
Q)
j5
The system electromagnetic environluent
Lightning protection
Static electricity
Grounding and bonding.
1
8
II
c::
0.1
'0..
0.01 ""--_-"'-_ _...&.-_--'-_ _....
0.01
0.1
100
FREQUENCY MHz
Figure 2.21
Limits for CS10 and CS11 NEMP
current injection
50
45
40
a:
35
~ 30
LU
-
:E 25
~ 20
15
10
I
I
I
I
I
I
I
I
I
I
5 --~-----~-------------------I
I
0-----1---""'-----------------'--1-t r - I - t d - i - - - - - - t f - - - - - - - i
~5 X 10-9
~ 38 X 10-
9
Figure 2.22
550 x 10-9
LIMIT FOR RS 05
US MIL Syn 461C NEMP
susceptibility
RS05: pulsed E-field (only for mission-critical
equipments located outside of an intentionally hardened area). The E-field pulse
shape to be used is shown in Figure 2.22.
A summary of the test identifiers, short titles,
applicability to parts of 461 C and detailed notes
is given in the form of a requirements tree in
Figure 2.23 [51].
The process of continuing to modify and update
this very important set of military standards is
continuing. A triservice committee has been set
up to further revise MIL STD 461/462/463 with
one of the aims being to eliminate the controversial area of defining and measuring narrow (CW)
and broad band (impulse) signals [51 J, as referred
to in Appendix 1.1.
It suggests guidelines for generating procedures to
define system compatibility demonstration tests by
using the normal system performance indicators
to reveal EMC failures. The system is tested
under real operational load conditions and interference is injected into it at critical points and at
a level which is 6 dB (or greater) than the worstcase levels created by the system or experienced in
the environment. The aim is to prove that a
margin of compatibility exists over and above the
level required for fault-free operation during a
simulated mission.
The imposition of MIL-E-6051 D on a system is
not contingent on the individual equipments
within it having been designed or tested to MIL
STD 461/2/3. I t requires a contractor to prepare
detailed proced ures and test plans to demonstrate
compatibility at system level. Clearly, such a
contractor could make considerable use of the
equipment test results from MIL STD 461/2/3 in
understanding the electromagnetic characteristics
of these equipments. One may initially choose to
model EMC at system level using computer codes
such as IEMCAP [53J to predict ranked systemlevel incompatibilities (starting with safety critical
circuits [54J) and thereby to better define a costeffective detailed test plan for satisfying MIL-E6051D.
Without such computation and subsystem test
work, meeting this requirement to demonstrate a
final check on complex system level compatibility
under operational conditions (simulated) cart be
lengthy and expensive in its preparation and
execution.
2.8.3 Other US military standards
A list of relevant EMC related US standards can
be found in Appendix 1.9.
2.9 UK tnilitary standards
2.8.2 MIL-E-6051D
2.9.1 Service and establishment-specific
standards
This standard is entitled 'Systems electromagnetic
compatibility requirements'. It is applicable to all
items of equipment within a definable system, the
performance of which may be influenced by
Military interest in EMC has been growing significantly in the UK since the mid 1960s following the
introduction of compact, complex, semiconductor
based equipment into platforms for all three
spikes 10~~
~
OV,151..1.s
20OV, 10 I..l.S
40o V, 51..1.s
UM 03 E field
2=-"7"M-=-=-H-=-z-·--=1-=-0--:0::7H"7"z-
UM 05 E field
H-z---:-15=-:0=---:k:-:-H-=-z-·-4:-=0-=-0--=-M-:-:""H
UM 04 E field
---2~-=-M:-:-H-'-z-·-:1--=-0-:O:-:-H"7"z-
Electromagnetic ffield
Transients
RS 03 E field
"7"14-:-:-:kH--:-z-·-4-=-=0-=O=c-":H-=-z-
RS 05
I
1
PAR'
I
.
.
.
CS 11
Damped sine trans.
Cables
CS 10 Damped sine trans.
Pins
CS 09 Structure current
60 Hz -100 kHz
CS 07 Squelch circuits
CS 06 Spike power leads
100 V, 10 Jl s
200 V, 1511 s
200 V, 101..1. s
400 V, 5 Jls
CS 05 Cross modulation
30 Hz -200Hz
CS 04 Rej. of Undes. signal
30 Hz· 200Hz
CS 03 Intermodulation
15 kHz -100Hz
CS 02 Power-inter. leads
50 kHz - 400 MHz
H field
30 Hz - 50 kHz
l
UM 05 E field
150 kHZ - 100Hz
UM 04 E field
14 kHz -1000 MHz
UM 03 E field
150 kHz -100Hz
RE 03 Spur & harmonics
Radiated technique
I
I
II
· .. · ..
· .. ·..
· . . ·.
.
.
.
UM 05 Power lines
50 kHz - 50 MHz
UM 04 Power lines
15 kHz - 50 MHz
CE 07 Transients
Time domain (power)
CE 06 Antenna terminals
10 kHz - 260Hz
receivers
TRS (key up)
TRS (key down)
I
I
L
I
T
I
·. · ..
·.·. · .
··......
.1. ·.
·.·.·.
·. . .
.
.
2 3 4 5 6 7 9 10
p
r-~-C-O-ND~U-C-TE-D---'
Power & interconnect
up to 15 kHz
I
CE 03 Power & interconnect
15 kHz· 50 MHz
CE01
I
EMISSIONS
2 3 4 5 6 7 8 9 10
RADIATED
RE 02 E field
14 kHz ·10 OHz
RE 01
I
Figure 2.23 MIL Syn 461C
! •••
· . · .. ·
· ·.·. ·
· · .·..
· ·. · ..
·. ··.....
·. · ·
··.. ·. ..
·. ·. .
·
· ·. .
· ·..
Power leads
30 Hz - 50 kHz
I
CONDUCTED
· ·....
· .·.
·.
·. ··. ..
· .....
· ·..
CS01
I
..-----:-1-----,
2 3 4 5 6 7
I
I
2 3 4 5 6 7 9 10 8
RADIATED
_H_fi_el_d
_--30 Hz· 50 kHz
RS 02 H field
=Po-w-e-r--=-fr-e-gu-e-n-cy-
RS 01
I
I
I
I SUSCEPTIBILITY I
~L--_
August 1986
~
~
Z
t'!j
~
t'!j
~
C
[f).
>
t'!j
~
z>
u
~
Z
o
[f).
t'!j
~
CJ
t'!j
~
o
i-:rj
~
o
o
to
U
>
~
>
Z
W
1'-.J
EMC STANDARDS AND SPECIFICATIONS
services. Early specifications such as FVRDE 2051
section 4 [55J, which was concerned with radio
interference from military vehicles, have been
progressively superseded by more modern
standards MVEE 595 and specific amendments
[56J in the same way as the US MIL STD 461/2/
3. Where possible these standards now form part
of the central (nonproject specific) UK standard
DEF STAN 59-41.
Each service tends to generate standards which
are designed to produce cost-effective EMC for
particular types of platform, weapons systems and
equipment which must function together in the
particular EM environment in which that service
operates. For example, MVEE 595 divides
military vehicles into two classes: FFR, vehicles
fitted for radio, and nonFFR, vehicles without
radio. In this way, the interference limits can be
more relaxed for nonFFR vehicles so that
acceptable electromagnetic compatibility can be
achieved economically without compromising the
performance of a particular system.
Where appropriate, military standards refer to
British Standards such as BS 727 (RFI measuring
equipment) and BS833 (vehicle ignition) for
example.
The navy has produced a set of standards for
equipment on board ships at sea which takes into
accoun t issues such as screening offered by metal
hulls below deck and the need to use electrochemically compatible metals for equipment boxes,
access doors and RFI gaskets where these are
exposed to a corrosive salt atmosphere.
Examples of navy standards are
NWS 3 (amendments 1-4) 1981: Electromagnetic
compatibility of naval electrical equipments
NWS 1000 part 1 Chap. 5 1986. 'Electromagnetic
compatibility-design guide'
NES 1006 1988 [5 7J : 'RF environment and
acceptance criteria for naval stores containing
EEDs' (supersedes NWS 6)
In 1974 the Royal Radar Establishment produced
a comprehensive EMC standard RRE 6405 [58J
to cover the EMC performance of RRE (later
RSRE, now Defence Research Agency) controlled
projects. I t comprised three parts:
1: Guide
Terminology and definitions
Con trol and test plans
Related documents
2: Requirements/limits
3: Measurement techniques
This standard specified equipment classes (Table
A1.8.5 of Appendix 1.8) and contained a comprehensive set of limits and test methods (Table
A1.8.6 of Appendix 1.8) which could be applied to
33
100
>
:i.
90
RCE03
.,.....
Q
80
Q)
.~
a
~
co
"'0
Z
0
70
N
60
M
50
Ci5
Cf)
~
w
40
321l V
30
0.05 0.1 0.2
0.5
2
5
10
20
50
100
FREQUENCY MHz
LIMITS FOR HIGH FREQUENCY BROADBAND CONDUCTED VOLTAGE
N
140 r---
- . , . . - - - r - - - - - , - - - r - - - - . . - - - r - - - - - r - - r - -.......
J:
~
>
130
RCE04
:i.
.,..... 120
Q
~ 110
15
N
~ 100
co
"'0
M
Z
~
80 10 mV MHz-1
~
70 3.2 mV MHz -1
w
0.05
0.1
0.2
0.5
2
5
10
20
50
100
FREQUENCY MHz
LIMITS FOR HIGH FREQUENCY NARROWBAND CONDUCTED VOLTAGE
Figure 2.24
RRE 6405 conducted emission limits
Reproduced by permission
or HMSO
all three services. This was achieved by the use of
different limits in relation to land, shipboard and
air service equipments. See Table A1.8.7 of
Appendix 1.8. For example, the limits for RCE03
where a line impedance stabilisation network
(LISN) is used in the measurement of RF
conducted voltages show the progressive relaxation
of the limits from grade L. See Figure 2.24.
Many aspects of this comprehensive and clear
document have been carried over to DEF STAN
59--41 which is the current central UK military
E~1C standard. It too covers equipment for land,
shipboard and air use with various limits based
on equipment classes.
2.9.2 Project-specific standards
With the aim of economically achieving the best
possible EMC performance, many large military
projects have generated comprehensive EMC specifications specifically for that project. They make
reference to the general EMC standards which
exist but tailor the limits and tests to help ensure
good E~IC performance of the system with respect
to its particular operational mission and
environment. The generation of project specific
EMC requirements can also be of value in
harmonising the views of sections of industry which
commonly operate with national EMC defence
34
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
standards, when they form multinational collaborative ventures for large aerospace or defence projects.
Examples of project-specific specifications are
SPP-90003
SPP-90203
EA98 QO 10J
SPE-J-000- E 1000
Tornado IDS
Tornado ADV
EH 101 helicopter
European fighter aircraft
National project-specific EMC requirements are
also produced, e.g.:
rrS1527
TS 1727
Ptarmigan} communications systems
Wavel
2.9.3 DEF STAN 59--41 (1988)
This standard was first issued in March 1971 and
was revised as Issue 2 in August 1979. Until Issue
3 in 1986, individual establishment EMC specifications were invoked for land, shipboard and air
applications. Issue 3 of DEF STAN 59-41 was
intended to stand alone and contained many test
methods and limits which were differentiated by
equipment class, service use and grade. The June
1988 issue of DEF STAN 59--41 is in five parts:
1: General req uiremen ts
2: EMC management and planning procedures
3: Technical requirements, test methods and
limits
4: Open site testing
5: Technical requirements for special EMC test
equipment
The standard ou tIines typical electromagnetic
environmental requirements for equipment used
in the services but the limits may be tailored to
meet the needs of specific projects. I t covers all
equipments for military use that may give rise to
or may suffer from electromagnetic interference.
I t is invoked, wherever practicable, in all designs,
contracts etc. for equipment for military use.
Specific requirements for projects may be
generated based on DEF STAN 59-41 by
considering
Selection of appropriate types of test
Modification of the scope of certain tests as
a ppropriate
Modification of test limits to match the environ
mental requirements of the project
Consideration of transients or other infrequent
emISSIons.
The standard does not directly cover issues
connected with explosive, nuclear effects (other
than EMP), hazards to personnel or ignition of
fuels
by
electromagnetic
energy.
Suitable
references to other documents are made. rrhe
standard also does not cover immunity or
protection from lightning strikes and is not
concerned with spurious signal outpu ts, spectral
purity, IF rejection or intermodulation products
in connection with communications or other
sensitive receiver equipment.
Part 2 of the standard sets out the requirements
for management and planning procedures, which
are mandatory in order to ensure that potential
interference problems are properly addressed as
early as possible in the life of a project. Specific
actions are required:
An EMC co-ordinator should be appointed for
the project.
An EMC working group should be formed for
a complex project.
A suitable control plan must be developed.
EMC technical policies for screening, filtering,
grounding and bonding should be established.
Appropriate test plans must be prepared.
Suitable, test facilities should be available.
Configuration control must establish the build
standard of all items for test.
Part 3 of the standard defines the equipment types
that are subject to certain tests, see Table 2.5.
Table 2.5 DEF STAN 59-41 equipment types
Type 1
Type 2
Type 3
All equipments fitted with electronic
components
Motors, genera tors and electromechanical selectors (wi thou t electronic
control)
Relays, solenoids and transformers
The tests applicable to each equipment type are
indicated in Table 2.6. The application of DEF
STAN 59-41 tests are further tailored by
introducing the grading of limits in relation to
service environment. See Table 2.7.
Table 2.6 Equipment type and tests
Tests
All tests
All emission and
imported spike tests
Imported and exported
spike tests only
Type 1 Type 2
Type 3
Y
N
N
y
N
N*
N
N
Y
*DRE02 test at power frequency is required if EDT is
fed with AC power.
A list of DEF STAN 59-41 test methods and their
applicability to a service is given in Table Al.8.8
of Appendix 1.8.
EMC STANDARDS AND SPECIFICATIONS
The tests specified in DEF STAN 59-41 are
comprehensive, but great care has been taken to
make them as straightforward as possible to
implement in an effort to eliminate some of the
inconsistency that may be associated with EMC
measuremen ts. T ~sts are to be carried out in large
shielded chambers equipped with radio absorbent
material (RAM) if possible. See Figure 2.25.
SCREENED ROOM WALL
FILTERING
........
EUT
Detail
Air
Ship
One grade
Above decks
Below decks
Class A
All test methods
Class E
Class F
........
........
,
I
EUT
I
I
CASE
BOND
Grade
Class D
........
I
I
Use
Class B
Class C
INPUT / OUTPUT
TEST GEAR
MEASURING SET
Table 2.7 Grading oj limits
Land
35
CAS'E BOND
I
GROUND PLANE
Equipment within 2 m of
comms. antenna
2-15 m of comms. antenna
15-100 m of comms.
antenna
> 100 m from comms.
antenna
Shielded equipment
Civil standards are
adequate
}'igure 2.26
Test lnethod DGYE02: signal/control line
current 20 Hz-l00 MHz
DEI? STAN 59-41 (Part 3) /2
Reprod ueed by permission or H M SO
LIMITS FOR AIRCRAFT USE
Z
Q_130
(J)<S;.
~:::i.110
::2:_
WfJ) 90
0"0
~~
Ow
70
::>0:: 50
00::
DEF STAN 59-41 has many test method and
equipment layout features in common with MIL
STD 462. It could be considered somewhat in
advance of the current US MIL SPEC in respect
of its employment of wideband bulk current
injection tests for conducted susceptibility DCS02,
DCS04 & DCS05.
55
o
FEEDTHROUGH CONNECTORS OR
FEEDTHROUGH FILTERS
TEST ROOM AREA
cleared of any unnecessary
equipment and personnel
__I
FREQUENCY
LIMITS FOR LAND SERVICE USE
140r-----r-----,----r---~---r---..,
Z
o
~
EUT MONITORING
EQUIPMENT
OR TEST SET
150 MHz,20
30
10
""'-_......._ - - - - ' I . . o . - _........_ - - - I ._ _~_ _
10 MHz 150 MHz
10 Hz 100 Hz 1kHz
~
120
<c
-=
WfJ)
0"0
100
80
60
WI-
t; r5
40
~ ~
00
20
::>0::
100 MHz, 40
CLASS 0
100 MHz, 25
CLASS C
100 MHz, 10 CLASS B
~~~~-4
o
CLASS A & E
-20'--_--'-_---'_ _-.1-_ _. 1 . - - _........._ _.......
100
1 kHz 10 kHz
100 kHz
1 MHz
10 MHz 100 MHz
MAIN SCREENED ROOM
complete with RF absorber
FREQUENCY
LIMITS FOR SHIP USE
-__r--_
140 r - - - . , . - - - - - r - - - - - , , - - -__
Z
o
Ci5
120
;c
~ _:::i.
::2:
100
80
WfJ)
0"0
60
::>0::
o 0::
z::>
20
~ ~
Ow
EMC TEST EQUIPMENT
( sig. gen., power amps.,
receiver, etc.)
}zgure 2.25
8°
FEEDTHROUGH
CONNECTOR
GROUND PLANES
Suggested layout .for screened room complex
DEF STAN 59-41 (Part 3) /2
Reproduced by permission or HMSO
40
-20'--_..a.-._--'-_ _L . . . - _ . . . . I - _ - - I ._ _....I
100 Hz 1kHz
10 kHz
100 kHz 1 MHz 10 MHz 100 MHz
FREQUENCY
}-'igure 2.27
DE}' S T A,N 59-41 (Part 3) /2 ( DGYE02)
Reproduced by permission or HMSO
36
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
The adoption of fixed receiver bandwidths for
emission measurements means that the problems
normally associated with the interpretation of
broadband and narrowband signals have been
eliminated. A future revision of MIL STD 461/2/
3 may also adopt this approach.
An example of the test layout for DCE02 can be
seen in Figure 2.26 with the associa ted limits for
conducted emissions appropriate to air, shipboard
and land use in Figure 2.27.
A list of examples of some widely used UK EMC
civil and military standards can be found in
Appendix 1.9.
2.10 Following chapters
This book has been prepared with the aim of
guiding the reader from a simple introduction to
EMC in Chapter 1, through issues relating to
regulations and standards in Chapter 2, to a
detailed consideration of the sensors, antennas and
measuring apparatus used in EMC testing which
are discussed in subsequent chapters. In this way,
readers with some familiarity of the basics of EMC
can progress to the main body of information on
EMC testing in the most direct way.
An introduction to design techniques for EMC
has been provided in Chapter 12 to complement'
the emphasis on EMC testing. Much has been
written in detail elsewhere on EMC design and
the reader is referred to appropriate references in
the text of Chapter 12. Readers new to EMC and
who wish to cover the basic elements of design
before continuing with the details of EMC testing
in Chapter 3, may read Chapter 12 now and then
return to Chapter 3.
2.11 References
2
3
4
5
6
7
MERTEL, H.K.: 'International and European RFI
regulations'. EMACO Inc. 7562 Trade St., San
Diego, CA 92121, USA, also section 10/2 IEEE
conference on EMC) 1982
SHO\VERS, R.M.: 'Wide scope of IEC work on
electromagnetic compatibility problems', Trans.
South Afr. Inst. Electr. Eng.) Jan. 1982
DEF STAN 59-41 (parts 1-4). Ministry of Defence
Directorate of Standardisation, Glasgow, UK
KEISER, B.: 'Principles of electromagnetic compatibility' (Artech House, 1987, 3rd edn.)
NAMAS Executive, National Physical Laboratory,
Teddington, Middlesex, TWll 01 W, UK
GERKE, D.: 'A fundamental review of EMI
regulations', R.p'. Design, April 1989, pp. 57-62
MIL STD 1541 'Electromagnetic compatibility
requirements for space systems'. US Department of
the Air Force, Washington DC, October 1973
8 MIL STD 461 C 'Electromagnetic emISSIon and
susceptibility requirements for the control of electromagnetic interference'. US Department of Defense,
Washington DC, August 1986
9 VDE 0871 Equivalent to EN55011, CISPRll,
BS4809. Similar to FCC Title 47 pt. 18. Obtainable
in UK from BSI, Milton Keynes, MK14 6LE
10 FCC Title 47 parts 15,18 and 68 of the US code of
Federal Regulations, Federal Communications
Commission, Washington DC
11 VDE 0875 'Regulation for the radio interference
suppression of electrical appliances and systems'.
English translation available from BSI, Milton
Keynes, MK 14 6LE
12 WHITEHOUSE, A.C.D.: 'EMC Regulations
within Europe', Electron. Commun. Eng. J.) March/
April 1989, pp. 57-60
13 Radiocommunications Division of the Department
of Trade and Industry, Waterloo Bridge House,
Waterloo Road, London SE1 8UA, UK
14 89/336/EMC 'EC council directive on the approximation of the laws of the member states relating to
electromagnetic compatibility',
OJ!. J. Eur.
Communities) L 139/19, 23.5.89
15 'Electromagnetic compatibility product standards,
UK Regulations' Department of Trade and
Industry and Central Office of Information, INDY
J1896NE.40M, April 1993
16 'EMC directive, technical report part 2', New
Electronics) May 1993
17 'EMC and the European directive', one day seminar
papers. Assessment Services and Hewlett Packard,
Nov. 1991 (Assessment Services, Tichfield, Hants,
UK, Hewlett Packard, Stoke Gifford, Bristol, UK)
18 LOHBECK, D.: 'West German RFI laws and
regulations'. Interference Technology Engineers
Master 1988, pp. 302-342
19 'U riders tanding the FCC regulations concerning
computing devices'. OST Bulletin 62, FCC Office
of Science & Technology, Washington DC, May
1984
20 Standard J -551 C, 'Measurement of electromagnetic
radiation from motor vehicles (20-1000 MHz)'.
Society of Automotive Engineers, Warrendale, PA,
USA
21 Practice APR-93 7, 'Jet engine electromagnetic
interference test requirements and test methods'.
Society of Automotive Engineers, Warrendale, PA,
USA
22 Report AIR-114 7, 'EMI on aircraft from jet engine
charging'. Society of Automotive Engineers,
Warrendale, PA, USA
23 ANSI C63: 1980 'Specifications for electromagnetic
interference and field strength instrumentation,
10kHz-10GHz'. ANSI, 1430 Broadway, New
York, NY 10018, USA
24 HOOLIHAN, D.D., JOHNSON, J.W. and
WEBBER, C.L.: 'Compliance with Japanese
Standards creates opportunities'.
Interference
Technology Engineers Master 1988, pp. 291-344
25 'Limits and methods of measurement of radio interference characteristics of information technology
equipment'. CISPR publication 22, 1985, first edn.
EMC STANDARDS AND SPECIFICATIONS
26 'New radio interference regulations amendment 28/
9/89'. Canada Gazette part 2, vol. 122 no. 20
27 'Radio interference regulations amendment'. SOR/
88-475 Canadian government publishing centre,
Department of Supply and Services, Ottawa,
Ontario KIA 059, Canada
28 C108.8-M1983, Canadian Standards Association,
178 Rexdale Boulevard, Rexdale, Ontario M9W
lR3, Canada
29 MA.Y, C.R.: 'EMI and amended Canadian radio
interference regulations'. Interference Technology
Engineers Master 1988, pp. 84-90
30. LESCHAK, D.: 'Safety and regulatory compliance'.
Interference 1'echnology Engineers Master 1989,
pp. 325-354
31 TUV, TUV Rheinland of North Anlerica Inc., 108
Mill Plain Road, Danbury, CT 06811, USA
32 DUFF, W.G.: 'Fundamentals of electromagnetic
compatibility'. Interference Control Technologies
Inc., Gainsville, Virginia, USA
33 SMITH, C.W. and BEST, S.: 'Health hazards in
electrical environment (Dent, London)
34 CIPOLLONE, E., BEVACQUA, F. and AMICI, S.:
'Electromagnetic field measurements for radiation
hazards
evaluation'.
Interference
Technology
Engineers Master 1989, pp. 190-288
35 ANSI standard C95.1, 'Safety levels with respect to
human exposure to radiofrequency electromagnetic
fields,
300 kHz-100 GHz'. American National
Standards Institute, 1982, New York, USA
36 'Advice on the protection of workers and members
of the public from the possible hazards of electric
and magnetic fields with freq uencies below
300 GHz'. National Radiological Protection Board,
(IIMSO, 1986)
37 'Guidance as to restrictions on exposures to timevarying electromagnetic fields and the 1988 recommendations of the international nonionising
radiation committee', NRPB-GSII (HMSO, 1988)
38 DEF STAN 05-74/1: 1989 'Guide to the practical
safety aspects of the use of RF energy'.
Directorate of Standardisation, 65 Brown St.,
Glasgow G2 8EX
39 INIRIC 'Interim guidelines on the limits of
exposure to radiofreq uency electromagnetic fields in
the frequency range from 100 kHz to 300 G Hz' ,
Health Phys.) 1984, 46, pp.975-984. Updated in
Health Phys.) 1988, 54, p. 115
40 EEC articles 4 and 5
41 LE ROY, G.A.: 'Sur les incendies provoques par les
ondes hertziennes', Comptes Rendus 1991, 168,
pp. 244-247
42 'Control of high-frequency radar equipment'.
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
37
National Fire Codes vol. 10 Transportation,
Boston. National Fire Protection Association, 1972
'Electromagnetic
radiation
hazards'.
Ground
Electronics
Engineering
Installation
Agency
standard T.0.31z-10-4, 1970
'Naval shore electronics criteria: EMC & EM
radiation hazards'. Naval Electronic
Command, doc. Navelex 0101, 106, 1971
Hazards of EM radiation to fuel (HERF). N avsea
OP3565/Navair 16-1-529, vol. 1, Chap. 7
EXCELL, P.S.: 'Radio frequency ignition hazards',
Hazard Prevention, May /J une 1984
OB procs. 41273 and 42413. Ordnance Board,
Empress State Building, Lillie Road, London SW6
ITR
'The achievement of electromagnetic compatibility'.
ERA report 90-0106, Feb. 1990, ERA Technology,
Cleeve Rd., Leatherhead, Surrey, UK
SIEFKER, R.G.: 'Tailoring MIL STD 461B for
naval avionics applications'. Proceedings of IEEE
conference on EMC, pp. 387-395
SIKORA, P.A.: 'A comparison of MIL STD 461C
to the previously issued MIL STD 461B'.
Interference Technology Engineers Master 1988,
pp. 72-111
Electro-Metrics Company,
100 Church St.,
Amsterdam, New York 12010, USA
GOLDBLUM, R.D.: MIL STD 461/2/3 revision
process. Interference Technology Engineers Master,
1990, pp. 208-357
'Intra-system electromagnetic compatibility analysis
program (IEMCAP)'. Rome Air I)evelopment
Center, USAF
LEE. G. and ELLERSICK, S.D.: 'Methodology for
determination of circuit safety margins for MIL-E6051 EM C system test'. Proceedings of IEEE
symposium on EMC) 1985, pp. 502-510
'Radio interference from vehicles'. Fighting Vehicle
Research
and
Development
Establishment,
FVRDE 2051 section 4. (FVRDE is now Military
Vehicles
and
Engineering
Establishment,
Chobham, Surrey)
'Electromagnetic interference and susceptibility
requirements for electrical equipments and systems
in military vehicles'. MVEE 595, 1975
'Radio frequency environment and acceptance
criteria for naval stores containing EEDs'. NES
1006, 1988, Procurement Executive, MoD, Deputy
Controller Warships, Foxhill, Bath, UK (restricted
document)
'Requirements for electromagnetic compatibility of
electronic equipments'. RRE 6405, 1974, Royal
Radar Establishment, DRA, Malvern, Worcs., UK
Chapter 3
Outline of EMC testing
3.1 Types of EMC testing
relate the measurements made to field, current or
voltage standards to within a few dB. In many
cases it is sufficient to make comparisons between
two alternative items for test and check the
amplitude and spectral characteristics of emissions
or immunity to resolve a design question.
I t is an ad van tage for the electrical and
mechanical designers of the product to be
involved with these simple bench tests, perhaps
with assistance from an EMC engineer, as they
gain first-hand knowledge of the reasons why
EMC issues must be taken into account and
sometimes take precedence over straightforward
design preferences.
On large projects where there may be an EMC
control board and specialist EMC design engineers
in both the prime contractor's organisations and in
many of the subcontractor firms, these simple tests
should be carried out as a routine matter, having
been specified in the EMC control plans which call
for tests at all the various levels of development.
These control plans may require exploratory tests
to be carried out that are neither simple nor quick
to perform. For example, it may be that sophisticated measurements need to be made to gather
information about the RF induced currents on an
existing system or installation, as a guide to the
EMC design features of a new type.
Whatever the scope and scale of these
preliminary tests, they will help to build up a
picture of the electromagnetic behaviour of the
equipment and give an insight into the optimum
design solu tions.
3.1.1 Development testing
A key element in cost-effective EMC design and
certification of a civil or military equipment or
product is careful programme planning. The
EMC aspects of the project must be considered at
all stages and may require some design and cost
compromises to be made. The particular solutions
arrived at will of course be determined by specific
project conditions, but it is vital that the existence
and timing of decisions involving electromagnetic
compatibili ty are known and as far as possible
planned for.
To this end, it is advantageous to be able to
submit key components, circuits, boards, cable
forms and hardware such as cases or racks, to
quick and simple tests during the design process.
In this way it is often possible to differentiate
more easily between the EMC attributes of
competing designs than by calculation or
computer modelling (which may be inappropriate
for small projects).
Simple tests carried out on the bench, with
perhaps a signal generator, oscilloscope and
spectrum analyser, can help to build a sound
design based on a number of small tests devised to
resolve EMC queries as they arise. This activity
also allows the designer or EM C engineer to build
up a broad picture of the 'electromagnetic
landscape' of the system being developed. This
will help to put into context particular EMC
issues which rnay arise during the design task.
For example, it will be possible to balance the
effort and programme funding devoted to case
screening, compartment filtering and screened
cable design, to ensure that no one feature is over
designed and too costly for the EMC performance
which will be achieved as a whole. These simple
bench tests can be carried out in minutes rather
than hours and many will not require the use of a
screened room, although setting up such tests on
an RF ground plane in an electrically quiet
corner of the laboratory can be an advantage.
Measurements are made at close range with
inexpensive simple E- and H-field sensors, small
current probes or high-impedance RF voltage
probes. They need not be accurately calibrated to
test house standards but it should be possible to
3.1.2 Measurement to verify modelling
results
On large projects, or in cases where it is inappropriate or prohibitively expensive to test a
critical EMC design feature, it may be necessary
to model the situation in a computer to gain
enough information about options and possible
solutions to 'enable the design to progress. The
models used may be relatively simple and
inexpensive to acquire and run. The results and
limitations of simple models are usually well
understood and data are used only as a guide.
This is the case for exampIc when calculating the
capacitative crosstalk between parallel wires [1, 2J
or the transfer impedance of shielded cables [3].
38
OUTLINE OF EMC TESrrING
In some situations, however, large models (such
as numerical electromagnetic code, NEC [4])
may be complex and the limitations on the
validity of the results may be difficult to
determine. In these cases it is necessary to
construct careful experiments based on specific
and simple situations where the results can be
calculated analytically and
the measured,
calculated and modelled results can be compared
and any modelling errors estimated. In this way it
is possible to gain confidence that the complex
computer model being used is well behaved and
its predictions are meaningful.
An example of such a situation is where a system
in a complex metal case is being tested in an RF
anechoic chamber and it is required to assess the
surface currents induced in the casing by planewave free-space illumination [5]. In such a
situation it is possible to create a patch model of
the system casing for input to NEC and model its
behaviour. One might also model a simple short
fa t dipole antenna of similar proportions to the
metal case, calculate the induced current pattern
using an analytical approach [6J and make
careful measurements in a high performance RF
anechoic chamber.
The aim is to assess the agreement between the
analytical solution and the measurements for the
simple case and then to compare these with the
computer model prediction and estimate the size
and nature of any model errors. The model may
then be run with the adopted patch configuration
of the system casing with increased confidence.
A great deal of reliance can be placed on
computer models that are used to support the
EMC design of large projects and it is vital that
the predictions are questioned and tested whenever
possible by comparison with measurement.
3.1.3 Preconformance test measurements
It is best practice to build on the development
testing which takes place during a project, by
checking the EMC performance of complete
subsystems or prototype equipments against the
specification by testing them in a semiformal way
using the test methods associated with the
specified standards. This practice requires access
to an appropriate test house or suitable company
facility. Consequently, the test can sometimes be
expensive and is reserved for confirming EMC
design progress at key stages of development
where screening, grounding, filtering, cable and
structure policies are to be fixed.
Preconformance test checks need not attempt
to cover all the specified tests listed in the
standard. They may concentrate only on
emiSSions or immunity or a wide range of tests
39
may be carried out for example on safety or
performance critical items.
If these tests are performed by an external test
house then it is vi tally important to select a
laboratory which is not only competent to carry
out the testing using the specified methods, but
one which can also analyse the resulting data and
interpret them to give clear guidance to the
customer for improving the design should this be
required. These semiformal tests are best carried
out in the company's own facilities if they are
available, as there is no substitute for hands-on
experience by designers and EMC engineers in
assessing equipment performance against the
specified standards which the final product must
meet.
Simple development and preconformance test
facilities can be constructed for a few tens of
thousands of pounds. Well appointed EMC test
facili ties wi th large semianechoic chambers can
cost around a million pounds to build but they
can usually be hired for a few thousand pounds
per day.
Both large and medium-sized projects make use
of development models which are dedicated EMC
test beds [7J on which a variety of assessments
can be made during the design phase and a good
reference database can be constructed. These
EMC physical models can then be subject to the
semiformal tests towards the end of development
with increased confidence that the preprod uction
and production items submitted for test will meet
the EMC requirements.
3.1.4 Conformance testing
The final stage of testing formally demonstrates
whether the equipment or system will meet the
EMC limits set out in the standard against which
it was designed. The contractor should have
confidence that the equipment will meet these
limi ts, as preconformance tests on critical
subsystems and iterative design testing will have
contributed to a full EMC database on the
equipment in line with the EMC control plan for
the project. Conformance testing should be for
confirmation of compliance; there should be no
surprises at this late stage.
The exact circumstances surrounding confor
mance testing will depend on a number of factors:
(i)
The constraints on the conformance test
station imposed by the appropriate national
law governing the registration, sale and
operation of the equipment being submitted
for test. In the past, some countries have
specified the use of central national test
laboratories for certain conformance tests.
40
A HANDBOOK FOR EMC TESTING AND MEASUREMENT'
The conditions con tained in the con tract to
supply the equipment may have a section
devoted to the EMC. Conditions with
regard to conformance or acceptance tests
may be laid down in such a section. I t is
possible that the procuring authority will
specify the conformance test house to be
used. I'his can sometimes be his own facility.
The type of conformance testing undertaken
will depend on the specification to be met,
e.g. system level or equipment level, and on
the size and complexity of the equipment
under test. Not all certified test houses will
be able to cover every specification for both
civil and military use and may not be able
to accomrnodate large, distributed or
complex E-UT (equipment under test). In
general, test houses have facilities that are
ei ther directed to testing civil/commercial
equipment or to military equipment.
with the rapid expansion of the need for
as a result of harmonisedEC
regulations
applied to almost all electronic
military and aerospace test facilities have
more active in the commercial field. Even
for tests on military systems, few industrial
would have all the facilities to carry out
acceptance
of for example a new aircraft
without the support of the procurement or
authorities to provide a flight test range
environment for mission electroYrl'lcrr\""r'lI' environment simulation.
to the specialisations and limitations
which most test houses will have, the selection of
a
will depend on the civil or
nature
the product and its size. Test
facilities m.ay only be able to support limited
'-'.....,"'~~,'J-'--'-'-'IJ of
for conformance testing:
"r>.'n-lr'.':lYllP."
f>r'\p.r·--:\t-l,n.Yl<:l1
Commercial equipment (small < 1 m cube)
Commercial equipment (large or distributed)
Commercial equipment (as installed)
Military equipment (small < 1 m cube)
Military equipment
or distributed)
Military
safe service
worthiness)
acceptance trials)
1'he technical details of EMC test equipment and
conformance
rnethods applicable to these
of
are discussed in detail in later
1-L>r.. r."V",.o.0
3.1.5 Conformance test plan
Whatever the equipment, specification, test
method or test
it is important to work
to a preprepared
where necessary,
customer approved) test plan. 1'he plan will have
been called for by the project EM C control plan.
The size, content and style of the test plan will
vary depending on the type of conformance test.
For example test plans for equipment being tested
to MIL STD 461 must be prepared in accordance
with DI-EMCS-80201 [8J and it is difficult to
generalise with regard to the contents of possible
conformance test plans.
They can be written by the equipment design
authority contractor or can be subcontracted to
an EMC consultant, who as an independent third
party, will liaise with the test house on the contractor's behalf. Or test plans can be written by the
selected test house as part of the testing contract.
In any event, the plan will contain information
from both the equipment contractor and the test
house in order that planned, accurate and
trouble-free testing can be conducted quickly for
the rninimum cost.
Test plans should include as a minimum the
following information to be supplied by the
equipment design authorityj.contractor or the test
house:
Functional and physical description of the item
to be tested detailing its purpose, method of
operation, modes of operation, interfaces to
external objects
Performance and modes of operation should be
identified as
critical
mission or performance critical
reversionary or backup modes
self test/check/calibration modes
Statement of the objectives of the conformance
test
Statement of the standard or specification
against which the item shall be tested and a
list of tests to be performed
Statement of any tests not to be performed, or
limitations of tests to be performed
List of applicable documents with regard to
the EUT, e.g. operating manuals etc.
reference to addi tional information in the
con trol plan
rrime schedule for the tests with daily test goals
including
EUT
position,
1-'est layouts
orientation, details of cable layouts and
bonding/grounding arrangements
Criteria for determining the locations of EUT
monitoring points and methods of monitoring
(immunity tests)
Applicable limits of performance degradation
(for immunity tests)
Description, methods of connection, position
and opera tion of any
associa ted
test
equipment needed to function the EUI' In a
OU1'LINE OF EMC TESrfING
representative manner to include all E UT
stimuli, instrumentation, electrical services,
cooling and hydraulic supplies
Electromagnetic and physical req uiremen ts for
a conformance test site (open range or
chamber testing) with special reference to
EUT size, weight, disposition and special
requirements (e.g. Dynamometer/rolling road
for vehicle testing).
In particular, the selected test house
contribute statements with regard to
must
Any modifications or limitations applied to the
test requirements set out by the EUT manufacturer/contractor for the test to be carried out
The necessary approvals from a national
quality organisation to carry out the specified
conformance tests
1'he state of calibration of all equipment to be
used (including screened rooms) and the
source of such calibration
Test equipment, including sensors, receivers
and recorders (type and serial numbers) to be
used in the tes t
Test methods to be employed and relevant
procedures
Standing orders and safety proced ures
Experience of testing staff who carry out the
work
An agreed test programme plan
The nature and content of test reports (e.g. for
reports on MIL STD 461 tests these should be
in conformance with MIL STD 831)
Delivery date for the test report, and
An estimate for EUT setup and stripdown
times and consequent facility occupation
(usually charged at a lower daily rate than for
a test day).
Test houses are usually booked well in advance
and it is prudent to fix a date and duration for
the testing and then stick to it. Setting the test
date can be difficult as the manufacturer will
have to balance a desire to set an early date to get
the product to the market quickly, against the
possibility of delays through development over
runs which could cause him to miss his slot and
perhaps not get another for some months. If slots
are missed and the selected test house is full,
manufacturers may have to change test house and
modify the test plan.
The manufacturer has to make the test date
judgment in the light of dates available at
suitable test houses. If the equipment is large and
complex and is to be thoroughly tested to an
involved specification (usually for a military
project), there may be very few test facilities
which can accommodate the equipment and there
41
will be limited scope in setting the test date.
This explains why many of the larger and more
established test houses are within military
equipment or aerospace manufacturers, as they
need the assurance of being able to test according
to the dictates of their project programmes rather
than by the availability of external test facilities.
As EM C testing becomes routine in the
commercial sector, larger electronics corporations
are setting up similar extensive in-house test
facilities. The number of test facilities which can
carry out testing of commercial electronic
equipment to the European EN standards or the
US FCC regulations is increasing all the time, but
there is predicted to b~ a shortfall in the mid
1990s in the UK when the full impact of EEC
harmonisation Directive EEC/89/336 is felt across
the whole of the electronics industry.
If the manufacturer can justify the return on
investing in an in-house EMC test capability then
most regulations and specifications permit self
certification of an equipment. A small in-house
facility may start with development testing and
grow to meet the company's developing
requirement for EMC conformance testing.
3.2 Repeatability in EMC testing
3.2.1 Need for repeatability and accuracy
The basis of the scientific method is founded on the
theoretical postulation and experimental verification of propositions. Thus the need for
experiments and measurements to be conducted
in a well ordered, accurate and repeatable
manner is fundamental if hypotheses are to be
confirmed or denied. These experiments must be
able to be repeated by others, and only when this
has been done is a consensus established with
regard to the validity of the theorem or notion.
In the case of practical engineering, the need for
careful test rnethods which can be carried out to
yield accurate and repeatable results is just as
important as in basic science. Indeed, in the
practical
world
of near
market
design,
developmen t and sale of electronic products
which are covered by national and interna tional
laws (including those relating to EMC and
electrical safety), it is vital that accurate wellfounded test data can be generated to support the
release of a product. Failure to certify the electromagnetic compatibility of a product to a
recognised standard is not only an impediment to
successful sales but can be an infringement of the
law, for which individuals within a company can
be held responsible.
EMC conformance measurements can influence
the success or failure of a product and thereby affect
42
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
the prosperity of the company which is developing
them. For electronic engineers engaged on projects
both large and small, understanding EMC test
methods and the limits of accuracy which may be
expected is becoming ever more important.
Accurate EMC measurements are essential for
Engaging in disputes over product liability
Ensuring system or product functionality in its
intended EM environment, and
Cost-effective EMC in product development.
It is an unfortunate fact that some EMC measurements are difficult to undertake simply and
repeatably. Increasingly in situations where
legislation is involved and litigation may turn on
EMC test data, every effort must be made by
members of the EMC community to define,
specify, understand and work to agreed test
methods which yield the most reliable results.
Many years of con tin uous effort by engineers
and regula tory committees go into developing
and ilnproving test methods in the light of realworld measurement experience to arrive at test
methods which are technically meaningful,
economic to conduct and are as reliable,
repeatable and accurate as possible. Such test
methods should be regarded with respect and
followed carefully as they embody the collective
experience of many people. They should not,
however, be followed blindly, and an effort should
be made to understand how the tests were
originated and developed and where they are still
difficult to perform, or may be inadequate or
inaccurate in some way.
EMC symposia held throughout the world have
sections devoted to new or improved test
techniq ues with a view to improving accuracy
and repeatability. Such technical development
accoun ts, in part, for the con tin uous changes to
EMC standards and specifications.
3.2.2 Accuracy of EMC measurements
Measurements of fundamental quantities of mass,
length and time have reached levels of extreme
accuracy with the advent of lasers and atomic
clocks. For example, time and frequency can be
measured accurately to about 1 part in ten to the
power 13. In everyday engineering some
quantities can be measured in the work place to a
fraction of a percent regularly and without effort.
Unfortunately,
EMC
measurements
of
quantities such as electric and magnetic field
strengths, power density and wave impedance,
surface and cable currents over a very wide
frequency range from Hz to GHz, are not particularly easy to conduct or to repeat. When wavefield
measurements are made in relation to equipments
being tested which do not have known electromagnetic characteristics, e.g. radiation pattern, farfield distance, etc. and are conducted in imperfect
surroundings such as screened enclosures which
give rise to multiple signal reflections, then considerable errors can arise.
A full discussion of EMC measurement errors is
given in Chapter 11 and follows the detailed
description of the various probes, sensors and
antennas used in testing. In this section a
preliminary indication is given as to the source
and Inagnitude of some of these errors such that
EMC measurement accuracy may be compared
with more familiar measurements.
Consider a typical EMC measurement system as
shown in Figure 3.1. The sources of EMC
measurement error will depend on
•
•
•
•
The accuracy of the measurement meter,
usually an EMI receiver, spectrum analyser,
power meter or other sensitive calibrated
measuring device.
The nature of the sensor or probe connected to
the meter. It is important to know what
quantities it actually measures, whether it
loads or disturbs the quantity being measured
and whether its output is an average over
space Qr time. Such questions apply particularly to wavefield measuring sensors or
antennas.
This
area
of
measurement
uncertainty
has
prompted
considerable
research by national standards bodies,
academics and practising EMC engineers into
defining exactly the characteristics of specific
antennas, what they actually measure in a
given test situation, and how to calibrate them.
The connection of the sensor Ian tenna to the
receiver or measuring meter can play a
significant part in introducing errors into the
measurement. Anomalies of up to 10 dB have
been observed with regard to the movement
of antenna cables on open test sites [9].
The surroundings in which the test is being made
have a major impact on wavefield measurements. EMC tests are usually carried out in
a laboratory with a ground plane on a bench
for conducted EMI tests
a screened chamber, possibly lined with radio
absorbent material (RAM) for military
radiated emISSIon and susceptibility tests.
Errors have been reported of 17 dB in measurements between standard antennas in RAMlined chambers [10 J
an open site, sometimes referred to as an OATS
(open-air test site) for commercial radiated and
conducted emission tests. Errors of around
10 dB have been reported concerning just the
calibration of open sites [11, 12J
OUTLINE OF EMC TESTING
SCREENED ROOM TEST CELL
EUT AND CABLE PLACEMENT
~SUREMENTSENSOR
UNKNOWN RADIATION FIELD
43
MEASURING METER - EMI RECEIVER
OR SPECTRUM ANALYSER
(A BICONIC ANTENNA IN
THIS EXAMPLE)
CALI BRATION ERRORS DRIFT ERRORS
EQUIPMENT FAULTS
EXTERNAL SIGNALS REACH ANTENNA
AND CONFUSE MEASUREMENT
+
<i 0
C.tt8(
;
12 0 ;:'-1.1::'
!V0r:
I-t(
o
000
UNBALANCED CURRENTS
FLOWING ON MEASUREMENT CABLE
INTERACTION BETWEEN ANTENNA
AND CABLE
UNKNOWN NEAR FIELD I FAR FIELD
DISTANCES FOR RADIATED EMISSION
COMPONENTS
~
RADIO ABSORBENT MATERIAL
HELPS TO MINIMISE REFLECTIONS
METALLIC FLOOR - GROUND PLANE
~
,
MUTUAL COUPLING OF ANTENNA ~
TO ITS IMAGE CHANGES ITS
CALIBRATION
#i\
~: ~
ANTENNA IS PHYSICALLY LARGE AND
AVERAGES THE FIELD STRENGTH
\ ~,
"
tI,'
ELECTRICAL IMAGE OF ANTENNA
IN GROUND PLANE
'1\
I
I I \
I I \
I \
',I ;
~4I~
Figure 3.1
Possible sources of measurement uncertainty in a measurement oj'radiated emitted jield strength
the actual installation where the equipment is
to be used. This is usually confined to large
systems which may occupy a whole building,
such as a central computing facility or a
telephone exchange. Problems encountered in
carrying out such testing have been reported
and discussed [13 J.
In each of these locations the surroundings will
affect and sometimes dominate the accuracy of
EMC measurements which are made, particularly
radiated emission and susceptibility measurements. Multiple reflections from the inside of a
screened room have been reported as leading to
errors at some frequencies of up to 50 dB in field
strengths [14 J.
The radiated-field measurement errors are
further complicated by the interaction of the
measuring meter with the connecting cable and
the antenna, which manifests itself as a VSWR
mismatch. The cable also acts as a parasitic
element to the receiving antenna and disturbs the
field being measured [12]. I t can also act as an
active element if the antenna or sensor is
unbalanced and a significant common-mode
curren t flows on the outer of the connecting
coaxial cable [9J. Thus the construction of dipole
antenna baluns with low leakage and good
balanced transformer properties is important in
minimising interactions between the antenna,
cable and receiver [15-1 7].
Significant errors can be in trod uced into
radiated EMI measurements by the interaction of
the antenna and the ground plane at an open site
or the walls of a shielded chamber. Such effects
can be understood in terms of the mutual
im pedance between the test antenna and the
electrical images set up by the conducting planes.
Monopole antenna input impedances can vary
wildly with frequency by an order of magnitude
or more inside shielded chambers [18-20J.
Such variations will not be allowed for in the
antenna calibration factor and will appear as a
measurement error. Because the frequency
dependent antenna impedance variation will
interact with the mismatched antenna cable, the
measured field strength against frequency will be
a function of the particular antenna at a
particular location in the screened room and with
a particular connecting cable which is laid out in
a particular way.
•
One of the largest sources of error is that
introduced by the configuration of the EUT
itself. The precise layout of cables which
cond uct RF currents from the energising
source (the E UT) will significantly affect both
the amplitude spectrum and the spatial distribution of current along the cables. This in
turn will affect the field radiated from it.
Changes in cable length or shape will affect
the cable resonance and the nature of the
conducted and radiated signals particularly at
frequencies around cable resonances where
changes of 10 dB have been reported for
various ways of bundling the same cable [21 J.
44
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
3.2.3 Implications of repeatability of
EMC measurements
From this overview of some of the issues which
determine the accuracy of EMC measurements it
is clear that radiated measurements in particular
are generally
(i)
(ii)
(iii)
(iv)
more complicated than some more common
measurements of physical dimensions such
as mass, time, pressure, or direct voltage or
current
the measurements cannot be easily isolated
from the surroundings in which they are
being made
the full nature of the object being
measured (in the case of an EDT) is not
known and it is far too time consuming
and uneconomic to investigate it fully such
that the most appropriate measurements
of maximum radiated field strength, for
example, may be made over a wide range
of freq uencies
the measurements are consequently far less
accurate than those for more common
quantities. In general it may be supposed
that conducted current measurements can
be made with a repeatable accuracy of
around 6-10 dB, but radiated measurements can contain errors in excess of 20 dB.
White [22J indicates that under some
circumstances total measurement uncertainty
at some frequencies can be as high as ±40 dB
for radiated EMC tests.
With this level of uncertainty in the repeatability
of these costly EMC measurements and the legal!
financial importance of being able to prove that
an equipment meets the national and international EMC standards before it may be sold or
imported into a country, it is clear that pressure
from government standards and regulatory bodies
together with industrialists and engineers will
gradually result in developing higher accuracy
EMC test methods.
There are those, like T.]. Dvorak in Switzerland
[12J, who believe that: 'A real improvement would
mean adopting entirely new concepts based on
recent advances in inverse modelling and modern
computer technology or even to completely
abandon the measurement of radiated fields in
favour of conducted measurements which still
have a large developing potential'.
I t is conceivable that electronic products of the
future will be released against specification limits
which are computer derived from standard
calibrated source current distributions which
simulate the EDT. The EDT conducted current
patterns would be measured and a computer
would calculate the full 3D wavefield (including
radial componen ts in the near field) as a function
of distance which would be compared with a new
type of specification.
As the need for more accurate results intensifies
in the coming years and the cost of manpowerintensive testing increases while the cost of
computer modelling decreases, there may be a
powerful incentive to move towards Dvorak's
technically superior computer simulation methods
for EMC clearance rather than relying on
measurement. For the present, EMC testing with
all its difficulties and uncertain ties will con tin ue
to be carried out worldwide on an increasingly
wide range of electrical and electronic products as
the importance of EMC grows.
3.3 Introduction to EMC test
sensors, couplers and antennas
3.3.1 EMC sensor groups
Sensors and coupling devices for EMC testing can
be grouped basically according to whether the RF
coupling is by conduction and induction or by
radiation. In some cases the same coupling
devices can be used for signal injection and
emission measurement. I t is convenient to group
probes, sensors, couplers and antennas based on
coupIing mechanism and their use in emissions or
susceptibility measurement as shown:
Conduction and induction
Conducted susceptibility (CS) signal injection
Conducted emission (CE) signal measurement
Radiative coupling
Radiated susceptibility (RS) antennas
Radiated emission measurement (RE) antennas
3.3.2 Conduction and induction couplers
As an example, an artificial composite conducted
EMC test arrangement (CE and CS) is shown in
Figure 3.2 where the conduction and induction
couplers used in a wide range of emission and
susceptibility tests have been illustrated. The
direct conduction couplers include
10/lF low-inductance RF feedthrough capacitors
Line-impedance stabilisation networks (LISN)
Wideband RF capacitor, used in conjunction
with a cable break-out box
High-impedance wideband voltage probes
(oscilloscope probes)
Direct ESD injection.
OUTLINE OF EMC TESTING
10uF FEEDTHROUGH CAPACITOR _
TO STRIP °RFo FROM MAINS SUP?LY
45
~ ~~AL WINDING AR.OUND EUT BOX
~ MAGNETIC INDUCTION TEST
r".-----......
~
DISTRIBUTED CAPACITIVE
COUPUNG WIRE
CURRENT PROBE MEASUREMENT
OR CURRENT INJECTION ON
ON POWER UNES
/'or
INDUCTIVE
Figure 3.2
CAPACITIVE CABLE CLAMP
RF GROUND PLANE
RF coupling techniques usedJor conducted emitted (CE) and conducted susceptibility (CS) testing
Figure 3.3 Examples
oj coupler frequen(Y
coverage for typical
conducted EMC
testing
DEVICE FREQUENCY COVERAGE
COUPLING DEVICE
(Power line frequencies)
SPIRAL WINDING ( BOX)
SPIRAL WINDING (CABLE)
10 uF CAPACITOR
USNs
AUDIO TRANSFORMERS
TORROIDAL CURRENT PROBES
(SJ: 'ke Injection)
(Sp kes)
(Pm er frequ.)
INDUCTIVE CLAMP
CAPACITIVE CLAMP
DIRECT CAPACITOR INJECTION
ESD PROBE
HIGH IMPEDANCE VOLTAGE
PROBE
10
100
1k
10k
100k
FREQUENCY Hz
Induction couplers include
Cable and surface current probes
Spiral induction windings for boxes
Spiral induction windings for cables
Distributed capacitance parallel wires
Capacitive and inductive cable clamps
Indirect ESD to nearby conducting plane.
There are a large number of sensors and probes
which are commonly used to make EMC
measuremen ts by using direct connection or close
spaced induction. The approximate frequency
coverage of each type of coupler Isensor is shown
in Figure 3.3. The technical details of these
devices is discussed in subsequent chapters where
their use in carrying out typical EMC tests is
explored.
3.3.3 Radiative coupling - EMC antennas
Figure 3.4 shows a collection of typical standard
antennas used for radiated emission and susceptibility testing. The approximate frequency
1M
10M
100M
1G
coverage of these antennas is given In Figure 3.5.
They include the following types:
H-field loop antennas for measuring the magnetic
field component of an EM wave
Small shielded loop antenna (155 mm dia.)
Large shielded loop antenna (0.5 m dia.)
E-field monopole antennas for measuring the
electric component of the wavefield (with respect
to an RF ground plane)
1 m effective height rod antenna
Small battery powered ~ensor with fibre optic
readout for susceptibility field-strength levelling
Free-field antennas such as:
Long wire an tenna
Tuned dipole sets
Broadband biconic antenna
Logarithmic conical spiral antenna' (circularly
polarised) and log-periodic antenna (linearly
polarised)
Horn antennas of various sizes
Dish reflector type an tennas for microwaves
46
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
~IGH GAIN REFLECTOR MICROWAVE ANTENNA
~ ~ORNANT~
0/
SMALL LOOP "H FIELD" ANTENNA
_
.----:-;;:;C
--;to\S\ ~NCS
_
~m-~;30fn
SPECTRUM ANALYSER OR EMI RECEIVER
~m,3m,
.~RO\SS
LOG. CONICAL
LjSPIRALANTENNA
SIGNAL IN
o
000
10Hz - 40GHz
MONOPOLE ANTENNA
TUNED DIPOLES
PARALLEL PLATE LINES
TEM CELLS ETC (not to scale)
I
I
RF LEVELLING AMPLIFIER
CONNECTED TO
FIELD SENSING PROBE
via FIBRE OPTIC CABLE
I
BATTERY POWERED "E FIELD" SENSOR
WITH FIBRE OPTIC CONNECTION TO
FIELD LEVELLING AMPLIFIER TO CONTROL
FIELD LEVEL DURING A SUSCEPTIBILITY
TEST
LOOP ANTENNA
(H FIELD)
O
t--------
RF POWER OUTPUT TO
SUSCEPTIBIUTY ANTENNAS ....-
p"'igure 3.4
...
Antennas and sensors used in radiated emission (RE) and radiated susceptibility (RS) testing
Figure 3.5 Examples
of antenna frequency
coverage .for typical
EMC antennas
ANTENNA or SENSOR
DEVICE FREQUENCY COVERAGE
SMALL LOOPS
LARGE DIAMETER LOOPS
1m MONOPOLE
LONG WIRE
TUNED DIPOLES
-- ---- ------
--
-
BICONIC DIPOLE
LARGE LOG. CONICAL SPIRAL
LARGE LOG. PERIODIC
LARGE HORN
SMALL HORNS
-
-
--- -
SMALL LOG. CONICAL SPIRAL
DISH REFLECTOR + FEEDS
-
--
-
,.....
-
.......
FIBRE OPTICLY COUPLED
E FIELD SENSORS
PARALLEL PLATE LINES
T.E.M. CELLS
G.T.E.M. CELLS
10
Bounded-wave antennas usually used for susceptibility testing:
Parallel-plate lines
"rEM (transverse electromagnetic) cells
erawford cells
GTEM cells (gigahertz TEM).
3.4 References
WHITE, D.R.J.: 'A handbook series on EMI', vol.
3, section 6.3, pp. 6.20-6.21 (Formulas for
100
1k
10k
100k
1M
10M
FREQUENCY Hz
100M
1G
10G
1000
capacitive crosstalk between parallel wires) DWC
Inc., PO Box D,Gainesville, Virginia 22065, USA
2 PITT, A.D.: 'EMC guidelines'. BAe ST23357, Oct
1979, pp. 10.2-10.6. British Aerospace Dynamics,
Six Hills Way, Stevenage, Herts, UK
3 RICKETTS,
L.W.,
BRIDGES,
J.E.
and
MILETTA, J.: 'EMP radiation and protective
techniques' (Wiley) p. 147
4 BURKE, G.J. and POGGIO, A.J.: 'Numerical electromagnetic code (NEC) - method of moments'.
Technical document 116, Naval Ocean Systems
Center, 1981
OUTLINE OF EMC TESTING
5 PRICE, W.O. and CANAGA, K.W.: 'Accuracy
estimation
in
anechoic
chamber
testing'.
Proceedings of IEEE conference on EMC, 1985,
pp. 161-169
6 KING, R.W.P.: 'The theory of linear antennas'
(Harvard University Press, 1956)
7 'ESA GEOS spacecraft development control plan'.
BAe Dynamics, Filton, Bristol, UK, 1974
8 DUFF, W.G.: 'Fundamentals of electromagnetic
compatibility'. Interference Control Technologies
Inc., Gainesville, Virginia, USA, p. 9.22
9 DEMARINIS, J.: 'The antenna cable as a source of
error in EMI measurements'. Proceedings of IEEE
symposium on EMC, 1988, pp. 9-14
10 AG.ARWAL, N.K.,JOSEPH, P.C. and KESAVAN
NAIR, P.N.: 'Evaluation of shielded anechoic
chamber for EMC measurement'. Proceedings of
IEEE symposium on EMC, 1985, pp. 134-138
11 TSALIOVICH, A.: 'Absorber-lined open area test
site - a new type of EMC test facility'. Proceedings
of IEEE symposium on EMC, 1988, pp. 106-111
12 DVORAK, TJ.: 'Fields at a radiation measuring
site'. Proceedings of IEEE symposium on EMC,
1988, pp. 87-93
13 COONCE, H.E.: 'On premises emission testing of
digital switching systems'. Proceedings of IEEE
symposium on EMC, 1988, pp. 15-18
14 JOFFE, E.B.: 'Are RS03 limits in the HF band
realistic?'. Proceedings of IEEE symposium on
EMC, 1990, pp. 196-201
15 DASH, G.: 'A reference antenna method for
16
17
18
19
20
21
22
47
performing site attenuation tests'. Proceedings of
IEEE symposium on EMC, 1985, pp. 607-611
BERRY, J., PATE, B. and KNIGHT, A.:
'Variations in mutual coupling correction factors
for resonant dipoles used in site attenuation
measurements'. Proceedings of IEEE symposium on
EMC, 1990, pp. 444-450
BRENCH, C.E.: 'Antenna differences and their
influence on radiated emission measurement'.
Proceedings of IEEE symposium on EMC, 1990,
pp. 440-443
MISHRA,
S.R.,
KASHYAP,
S.
and
BALABERDA, R.: 'Input impedance of antennas
inside enclosures'. Proceedings of IEEE symposium
onEMC, 1985, pp. 534-538
McCONNELL, R.A.: 'An impedance network
model for openfield range site attenuation'.
Proceedings of IEEE symposium on EMC, 1990,
pp. 435-439
MISHRA, S.R.: 'Effect of ground plane and
chamber walls on antenna input impedance'.
Proceedings of IEEE symposium on EMC, 1988,
pp. 395-399
HUB lNG, T.H.: 'Bundled cable parameters and
their impact on EMI measurement repeatability'.
Proceedings of IEEE symposium on EMC, 1990,
pp. 576-580
'A two-part five-day comprehensive training course
in EMC, Part 2'. VG A15393, Don White
Consultants;' PO Box D, Gainesville, Virginia
22065, USA
Chapter 4
Measuretnent devices for conducted EMI
4.1 Introduction
Ridged horns
Horn-fed dishes
LF magnetic loops
Ferri te-cored loops
Leakage probes
The approach taken in this book with regard to
ordering and presenting information about the
dozens of sensors, couplers, probes and antennas
used in EMC measurement is to discuss them in
groups that are defined by the manner in which
they couple to the signals being measured. The
different physical processes related to each type of
coupling can thereby be appreciated and a
practical insight gained in to their operation
which is reflected in the structure of the various
test methods employing these devices.
Although this particular chapter concentrates
on coupling devices used in conducted EMC
testing, all the groups of sensors discussed in this
book, including radiated emission and susceptibility antennas, are listed here to show the
number of groups and to illustrate the range of
sensors considered.
Sensors are grouped as follows:
Devices for radiated susceptibility (RS) testing
•
•
•
Conducted emission and susceptibility tests (CE,
CS)
•
•
•
Direct connection devices
Line impedance stabilisation network
(LISN)
10 flF feedthrough coupling capacitor
Injection transformers
High-impedance voltage probes
Inductively coupled devices
Cable current probes
Cable current clamps
Surface current probes
Straight and spiral wire inductive coupling
Inductive loops around boxes
Ferri te wands or probes
Direct electrostatic discharge
Handheld spark generators
•
4.2 MeasureD1ent by direct
connection
Devices that are directly connected to the E UT
are of two types:
(i)
Devices for radiated emission (RE) tests
•
Free-field antennas
Short transmission lines
Long wire antenna
Biconic dipoles
I...Jog. spirals and periodics
Standard and ridged horns
Dish-type reflectors
Bounded-wave antennas
Parallel-plate strip lines
Crawford cells
TEM and GTEM cells
E-field sensors
Battery powered monopole sensors
Electrically short dipoles
Diode detection dipoles
Fibre-optic coupled sensors
Monopoles
Monocones
Radhaz monitors
Indirect ESD
Various metal plates onto which the spark
is discharged
(ii)
Radia ted emission antennas
Long wire antenna
Monopoles (passive and active)
Tuned dipoles
Biconic dipoles
Log. conical spiral
Log. periodic
Standard horns
48
Networks that produce a defined load
impedance as a function of frequency to the
circuit being tested. The most common
device of this type is the line impedance
stabilisation network (LISN).
Probes that can be connected to the circuit to
be measured wi thou t significantly altering
the RF voltages, currents and circuit
impedance. High-impedance RF voltage
probes commonly used with oscilloscopes,
transient recorders or spectrum analysers are
an example of this second type of direct
connection device.
MEASUREMENT DEVICES FOR CONDUCTED EMI
TO EQUIPMENT
UNDER TEST
4.2.1 Line impedance stabilisation
network
The development of the LISN goes back to the
1950s when early EMC engineers needed to
develop a means of providing a standard power
supply impedance network for aircraft, in an
attempt to correlate equipment EMC bench test
results with those carried out using actual aircraft
supplies. In the civil sector, the parameters of the
mains network were determined by analysing
many measurements of the RF impedance of
domestic, industrial and other supply systems [1].
The mean values were found to be well
represented by an equivalent circuit with 50 ohrns
in parallel with an inductance of 50 pH. Good
agreement was possible between several countries
and so this network was adopted by CISPR in
publication 16 [2J and has since been incorporated into a number of standards including
BS800jEN55014.
When an LISN jartificial mains network with a
defined impedance is used, it is possible to simply
and quickly measure the RF voltage as a function
of frequency appearing on the conductor under
test. The specified levels for the test are written in
terms of a measured RF voltage as a function of
frequency. Thus the voltage measurements made
using an LISN can be compared directly with
specified limits and many commercial standards,
such as BS800jEN55014, BS6527jEN55022,
VDE0877 and VDE0871, etc., specify conducted
EMI only in terms of RF voltage across a
standard LISN.
However, knowing the RF impedance of the
network also permits the calculation of the RF
curren t flowing along the cond uctor into the
LISN terminal. This can then be compared with
measurements made using alternative direct
techniques such as inductive current probes as
used in MIL STD 462 tests CEOI to CE05.
Practical LISNs fulfil three functions:
Filter incoming RF noise from the maIns
supply
Provide a known impedance as a function of
frequency to the equipment under test
(EDT), and
Provide a matched 50 ohm RF connection to
the EMI meter.
One of the most commonly used LISN designs is
that required for meeting tests CE02, CE04, CS02
in notice 3 of MIL STD 462 [3]. The circuit of
the LISN is shown in Figure 4.1a with its
impedance profile from 14 kHz to 10 MHz in
Figure 4.1b when the measurement port is loaded
with 50 ohms. Note that the EDT line impedance
is 50 ohm down to about 1 MHz. A second circuit
L (APPROX. 56uH)
A
8
49
TO POWER SOURCE
50A
15A
O.1uF
600V
Z1
C2
25 k ohm 20W
0.03uF
600V
R4
NC
Zs
50 OHM COAXIAL
TERMINATION IN PLACE OF RFI METER
(aj
(J)
:;E
I
50
0
UJ
40
()
Z
<t:
0
UJ
a..
~
30
LL
0
UJ
:::::>
20
....J
<t:
>
UJ
r-
10
:::::>
....J
0
(J)
co
<t:
0
0.014
0.1
1.0
10
FREQUENCY MHz
(bj
Figure 4.1
56p,H line impedance stabilisation network
( LISNj
( a) Circuit diagram
(b) US MIL-STD 462
is given for use in MIL STD 462 N3 which is
suitable for measurements over a higher frequency
range up to 50 MHz, see Figures 4.2a and 4.2b.
Figure 4.3 shows the basic circuits for three LISNs
required to carry out testing to CISPR 16, FCC
(MP4) and VDE 0876. Specifications BS3GI00,
NWS3 and DEF STAN 59-41 require the use of a
5 pH LISN for tests up to 150 MHz which incorporates special design elements to suppress unwanted
high-frequency impedance variations owing to
component self resonance. See Figure 4.4a for the
circuit details and Figure 4. 4b for the limits of
acceptable impedance with frequency.
DEF STAN 59-41 specifies the addition of a
10 pF feed through capacitor connected across the
power input to the LISN for AC lines and a
30,000 pF capacitor for DC supplies to further
stabilise the power supply impedance. Figure 4.5
shows the limits of acceptable impedance for the
LISN with the power supply terminal connected
to the case.
50
A HANDBOOK FOR EMC TESTING AND MEASUREMENT,
TEST
SAMPLE
L
COAXIAL
~g~~~~~~R
...__.....
MEASURING
SET
(aj
50
Iii'
E
..c
.2w
()
40
30
z
«
0
w
a..
~
20
z
(J)
::J
10
0
0.1M
10M
1·0M
100M
FREQUENCY Hz
(bj
Figure 4.2
US MIL-STD 462 HF 5 IlH LISN
( aj Circuit diagram (b j LISN impedance
TO EUT
TO MAINS SUPPLY
TO 50 ohm
RECEIVER
CISPR PUBL. 16
L150uH
TO EUT
TO MAINS SUPPLY
TO 50 ohm
RECEIVER
or 50 ohm
TERMINATION
FCC MP-4
TO EUT
>
TO MAINS SUPPLY
TO 50 ohm
RECEIVER
A 50 ohm 50llH design (9 kHz-30 MHz) is given
in BS727 which allows the connection of the EMI
meter to both the live and neutral terminals of the
power lead of the EDT by operation of a switch.
See Figure 4. 6a. Note the pi-section input filters
formed from L 1 , C1/R 1, C2 /R 2 . Figure 4.6b shows
the acceptable impedance limits.
The impedance profile of the higher frequency
5 IlH 50 ohm LISN (150 kHz-l 00 MHz) specified
in BS 727 is that given in BS3G 100. BS 727 also
defines the componen t values for a 150 ohm
resistive LISN, see Figure 4.6a. A more sophisticated 150 ohm LISN that allows measurement of
both the symmetrical and asymmetrical interference voltages from an EDT is specified in BS905
pt I/EN550 13, see Figure 4.7 .
LISNs are usually mounted on a specified
metallic ground plane alongside the EDT as in
Figure 4.8 and the EMI meter is connected via a
high performance low-loss coaxial cable to the
measurement port. LISN measurement ports on
lines which are not being measured are
terminated in 50 ohms. Typical narrowband
voltage limits (BS3G 100) for conducted interference measured in this way can be seen in Figure
4.9. Limits applicable to interference from
information technology equipment as specified by
FCC part 15 and the now superseded VDE 0871
(measured using a quasipeak detector in the EMI
meter) are given in Figure 4.10.
LISNs can be usedjust to provide a stable known
terminal impedance for EDT power lines and the
actual measurement of conducted current is made
using inductive current probes. This is the case for
test DCEOI in DEF STAN 59-41, see Figure
4.11a. The conducted current limits in this case are
specified in dB IlA not dB 11 V. See Figure 4.11 b.
The LISN is a widely used coupling and
standard impedance device which is easy to use
and has been incorporated into most commercial
and military EMC standards. It represents realworld power line impedances well and is an
inexpensive device, but is limited in respect of its
freq uency span and its upper frequency limit,
which is usually determined by spurious
component resonances.
The LISN can be used to inject an RF signal
directly onto a power line that feeds the
equipment under test. Consider the circuit of the
simple network shown in Figure 4.2a. The signal
is injected on to the line under test via the high
quality low-inductance/low-loss capacitor C 1 . The
series inductor L 1 provides a high impedance to
the injected RF being shorted out by the mains
circuit outside the test area. The capacitor C2
dumps any RF signal which passes the inductor
to ground and prevents it from contaminating the
external mains system.
Y
VDE 0876 Teil1
Figure 4.3
Various LISNs for use in testing commercial
electronic equipment
MEASURElVIENT DEVICES FOR CONDUCTED EMI
For details of inductor see table
I
"'TOSOohm
MEASURING
RECEIVER
}-'igure 4.4 LISN
suitab Ie for UK
BS3G100 Pt.4 Sec.2
( a) Circuit details
( b) Limits of
acceptable impedance
rl
C1
O.OS,UF
C2
TO.OSpF
,.....,................
51
,.......~~r~"r-,.
TO
EQUIPMENT
TO MAINS
SUPPLY
10
ohm
DETAILS OF INDUCTOR
CURRENT
RATING
INDUCTANCE
INSIDE DIA. LENGTH
A
~H
mm
mm
10
100
5
5
5
25.4
50
90
32
115
178
500
No. OF TURNS
CONDUCTOR
CROSS SECTION
mm
20
1.6dia
6dla
12.5 x 12.5 sq.
18
11
(aJ
80----------r-----------r---------.,.------.
(j)
E
60
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~
----------"".,.-',""
UJ
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<!
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1.0M
10M
___IL..._
...I___
100M
____'
200M
FREQUENCY Hz
(b)
Reproduced by permission of BSI
50 __---r---...,.---r------r----,----,------,
_
The use of an LISN in this way is required for
some conducted susceptibility tests such as MIL
STD 462 Notice 3 test CS02 (method B 150 kHz
to 65 MHz). Signal voltages of less than 1 V RMS
are normally injected but RF power of up to a
few tens of watts can be injected by this means for
a short time.
40
~
"§ 30
(II
:g.
w
o
20
z
(§
w
10
c..
~
0
-1 0 L------'......_ _..,.;._ _"--_---L._ _--I--_ _
10k
100k
1M
10M
~_----J
10
FREQUENCY Hz
* ACTUAL L1SN IMPEDANCE MUST LIE WITHIN THESE LIMIT LINES
Figure 4.5
LISN,for use with UK DEF STAN
59-41 limits for impedance against frequency
with supply or load terminal connected to
case
Reproduced by permission of HMSO
4.2.2 10 JlF feedthrough capacitor
MIL STD 461/2 calls for the use of a good quality
10 flF RF feed through capacitor which can be
used to provide a known low RF terminating
impedance on power lines in tests such as CEO 1,
CE03 and CS06. See Figure 4.12. In the spike
immunity test CS06, the RF short circuit
52
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
Figure 4.6 Dual line
LISN suitable for
use with BS727:
Radio interference
measuring apparatus
( a) -Circuit of 50 JlH
design (b) Acceptable
impedance limits
C3
L
R2 ~ -E
R3
I
: EQUIPMENT:
----1.._---;,-0 UNDER
I
I
TEST
I
MEASURING
RECEIVER
0-_..--.....
R2~
~
N
COMPONENT VALUES FOR 50 ohm I 5O,..H NETWORK
COMPONENT
VALUE
COMPONENT
R1
R2
R3
R4
R5
R6
10 ohms
5 ohms
1kohm
50 ohm
(short)
50 ohms
C1
C2
C3
L1
l2
COMPONENT VALUES FOR 150 ohm NETWORK
VALUE
COMPONENT
VALUE
1.2pF
8JJF
O.25J,1F
250,uH
50}lH
R1
R2
R3
R4
R5
R6
open
short
open
150 ohm
100 ohm
50 ohm
COMPONENT
C1
C2
C3
l1
l2
VALUE
open
0.251JF
O.1I-'F
short
short
(a)
100
r-------.,..--------.------,..--..,
;",''~~------------N--------­
,__fllllJ-----, ---------
50
en
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; ;;,;
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TOLERANCE +/- 20%
",; ; ;
;;
--;'
1'--10k
1--
...1.-
100k
1M
--1._--1
10M
FREQUENCY Hz
Reprod uced by permission of BS I
provided by the two capacitors ensures that the
full high-frequency spike voltage is applied to the
EDT power input. Because these capacitors are
intended for use with power lines they must
operate up to 600 V DC and be designed to
handle mains currents of more than 100 A
without significant loss. Such capacitors are quite
large, 85 X 85 X 70 mm, and are designed to be
bolted to the RF ground-plane or to the screened
room wall when being used as a power line filter.
The
RF
attenuation
characteristic
of a
commercial 10 JlF capaci tor (Solar 6512-1 06R)
[4] is shown in Figure 4.13.
4.2.3 RF coupling capacitors
High-quality
low-inductance
RF
coupling
capacitors are widely used in EMC testing to
(b)
inject RF voltages onto the power lines connected
to EUTs. The principle is to isolate the mains
low-frequency AC, or DC line voltage from the
signal injection RF power amplifier while
efficiently coupling the injected RF energy into
the power line circuit. Typical circuits may have
an RF impedance from tens of ohms up to a few
hundred ohms. The coupling capacitor must
therefore have negligible series reactance at the
lowest frequency of the test. The capacitor should
not exhibit self resonance at high frequencies
where the self inductance due to foil construction
or lead lengths becomes significant.
In MIL STD 461, a capacitor with a reactance
Xc < 5 ohms is required for the CS02 test over a
frequency range of 50 kHz to 400 MHz. This
requires a capacitor with a value of at least
0.1 fiF. See Figure 4.14. Practical coupling
MEASUREMENT DEVICES FOR CONDUCTED EMI
r-----------------------------------
5 :
~
0::
S
---~
I
R12
I
L
::>
o
u::
z
o
o
53
Figure 4.7 150 ohm
LISN for measuring
conducted interference
( EN55013
[BS905 pt.1])
~
....J
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I-
::>
a..
~
,r
(j)
I
~
I
z
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I
2
OUTPUT TO EUT
l_~monaifiiter il;'~;;:-ed- ----- - -- -
I
- - - -- -- -.1:--- - J
SWITCH S - Position 1 - symmetrical interference
Position 2 - Asymmetrical interference
Resistor values for ISO ohm LISN
Measuring
apparatus
Value
ohms
120
150
390
270
22
110
50
capacitors are constructed from a number of
different capacitors in a network designed to
minimise self resonance in the VHF and UHF
ranges.
Coupling capacitors are also used for exan1ple in
IEC 801 part 4 (BS6667) where high-frequency
transient bursts are injected into industrial process
measurement and control equipment. See Figure
4.15. The capacitors have a value of 33 nF which
results in a negligible impedance to the frequency
components of the 50 ns (50% width) voltage
spikes. Note also the use of ferrite damped
inductive and capacitive decoupling of the
injectors from the mains input.
The draft for part 5 of BS6667 of 1990 [5 J
considers the immunity of industrial process
control equipment to voltage surges. In this
Reproduced by permission of BSI
standard, capacitors with values of 9 or 18 JlF are
specified for injecting surges onto power lines and
smaller capacitors with a value of 0.5 JlF are used
for injection onto input/output (I/O) or control
lines. See Figure 4.16a. For line-to-ground testing
a series resistor of 10 ohms is used with the 9 JlF
capacitor for power lines and a 40 ohm resistor in
series with the 0.5 JlF capacitor for I/O lines. See
Figure 4.16b and 4.16c.
Boresero et al. [6J describe a current injection
method for evaluating the immunity of broadcast
receivers to RF interference based on an injection
capacitor. See Figure 4.17. The reactance of the
capacitor must be small compared with the
150 ohm resistive component of the total
generator and coupler impedance. Once more an
inductive/capacitive filter forms an integral part
LINE IMPEDANCE STABILISATION NETWORKS
(ONE FOR EACH POWER LINE)
.-------
POWER INPUTS
-----
AC or DC
50 ohm resistive termination
on line not being tested
Figure 4.8
Conducted emission measurement LISNs mounted on ground plane bench
54
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
MEASURING SET
POWER SUPPLY
BROADBAND CONDUCTED INTERFERENCE LIMITS
SCREENED ROOM WALL
80
W
C)
~
70
30,OOOJJF CAPACITOR FOR DC SUPPLIES
....l
0
>
60
N
WI
()~
z>
W=t
L1SNs USED TO PROVIDE
A DEFINED RF IMPEDANCE
FOR POWER LINES
50
0::,...
w(1)
u.. >
0::0
40
~en
30
W.c
.-0
0"0
Z
<!:
20
en
0
CURRENT PROBES
ARE USED TO MAKE
THE MEASUREMENTS
<!:
0
10
0::
en
0
10k
100k
1M
10M
EUT
100M
FREQUENCY Hz
GROUND PLANE
NARROWBAND CONDUCTED INTERFERENCE LIMITS
NORMALRFMEASUREMENTPORTS
TERMINATED IN 50 ohms
90
w
<:>
.<!:
..J
80
0
TEST METHOD DCE01
(POWER LINE CONDUCTED
INTERFERENCE 20Hz - 150MHz)
(a)
>
w
()
z
w
a::
w>
~=l
W,...
,-(1)
Z
_
70
(j)
.0
o
~ 130
60
~
~ 110
0>
0"8
50
Zm
(i5-o
~
90
~
70
~
50
"0
~
40
0
a::
a::
:J
z
<t:
z
w
30
10k
100k
10M
1M
100M
ffiLl..
0::
W
I-
FREQUENCY Hz
Figure 4.9
~
30
10 L -_ _J..-.._ _J..-..
10Hz
100Hz
Typical conducted emission limits using
LISN (BS3G100 pt.4 sec.2)
'--
1k
10k
' - - _ - - - L ._ _---L._ _- - '
100k
1M
10M
150M
FREQUENCY Hz
(b)
Reproduced by permission of BSI
Figure 4.11
of the coupler and isolates the wan ted signal source
from the injected interference.
The use of coupIing capacitors for injecting RF
interference into power and signal circuits is a
common technique. It is simple and inexpensive.
I t can be trouble free if good quality non self100 , . - - - - , . - - - - , - - - - , . . . . - - - - r - - - . , - - - . , - - - - - - ,
CI)
UK DEF STAN59-41 test DCE01
using LISNs (a) Use oj current probes
( b) Limits for aircraft use
Reprod uced by permission of HMSO
resonant components are used. The EMC test
engineer must take care however to ensure that
the connection of the coupling capacitor does not
lead to the following problems.
...J
W
>
W
...J
80
W
- - - CLASS A F C C -
()
r-------
Z
W
~$
0::"'-
I
60
~ ~
~~
CLASS A & C VDE
CLASS B VDE & FCC
OOJ
~"O
40
()
RECEIVER BANDWIDTH--I_---RECEIVER BANDWIDTH
200Hz
-19kHz
:J
o
... !
Z
o
()
20
r.....-_--'"_ _--lo-_ _--I,..-_ _- i -_ _- ' - -_ _- ' - - _ - - - '
10k
30k
100k
300k
1M
3M
10M
30M
FREQUENCY Hz
Figure 4.10
FCC and VDE interference limits for
conducted emission tests on IT equipment
using LISN
(i)
For AC power circuits
High-power line voltage can be coupled back
through the capacitor into the signal source and
damage the source output circuit. The power line
voltage fed back through the coupling capacitor
also must not damage the input circuit of any RF
voltage measuring meter which is connected to
monitor the injected RF susceptibility signal.
Some proprietary coupling capacitors (e.g. Solar
7415-1) have built in high-pass filters to the
power line frequency in the monitor output to
preven t this.
MEASUREMENT DEVICES FOR CONDUCTED EMI
(ii)
50
TRANSIENT
GENERATOR
~
::r:
TRANSIENT WAVESHAPE
10IJF CAPACITOR
10IJF CAPACITOR
-=-
SERIES INJECTION ON AN AC LINE
(a)
(b)
(c)
Figure 4.12
MIL STD 461 test using 10 J-lF capacitors
(a) Spike injection test (b) Test CEOI
(c) 10 J-lF Jeedthrough capacitors
55
For signal I/O and control lines
'The connection of a coupling capacitor can load
the signal circuit thus reducing the wanted signal
level below that specified for correct circuit
operation. When the interference voltage is applied
via the capacitor the ratio of the normal functional
signal to injected susceptibility signal will be artificially low and the EUT will tend to fail the test at
a lower level of injected interference than it should.
Direct
capacitive
coupling
via
lumped
components is not particularly suitable for circuits
operating at RF or carrying data with fast-rising
and falling (nanosecond) edges, as the high
frequencies will see the injection capacitor as a
low-impedance short.
4.2.4 Distributed capacitance couplers
The use of lumped injection coupling capacitors
has a number of technical drawbacks which have
been mentioned earlier. An additional problem is
the time, trouble and cost involved in making the
direct connection to the conductor under test by
splitting the cables or using special break-out
boxes. It may not be possible to make such a
connection at all in the case of overall screened
multiconductor cables or coaxial signal cables.
For some circuits to be tested, many of these
problems of direct connection can be overcome by
the use of distributed capacitance clamps if the
testing standards permit. Using such a device the
cable under test can simply be laid in the clamp
with no direct physical connection being made.
A device specified in IEC80 1 part 4 is shown in
Figure 4.18a. I t is used for testing as shown in
Figure 4.18b. Such a clamp however only has a
capacitance of between 50 and 200 pF for cables
of 4 to 40 mm dia. This low coupling capacitance
restricts efficient injection to high-frequency interference signals or pulses with fast nanosecond
risetimes.
In some cases it will not be possible to physically
place the signal or I/O cable under test in the
capacitance clamp owing to the inflexibility of the
cable in question or the size of the clamp. In such
circumstances IEC80 1 pt 4 permits the use of a
simple wire or conductive metal tape to be used
by placing it alongside the cable under test to
form a distributed coupling capacitor. See Figure
4.19. 1'he capacitance between the cable under
test and the injection wire should be adjusted to
be in the same range as for the purpose designed
clamp (50-200 pF).
Distributed capacitance probes can also be used
in conducted emission measurements. White [7]
illustrates a spaced wire technique on a ground
plane for
measurifig common-mode
cable
56
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
70
r-------.,-------~-------r_------~------__,.------___.
TYPICAL PERFORMANCE [SOLAR 6512-106R]
60
50
co
"0
SAE MINIMUM ARP-936 REQUIREMENT
40
CJ)
(/)
9
30
20
10
10M
1M
100k
10k
100M
1G
FREQUENCY Hz
INSERTION LOSS MEASURED IN a 50 ohm CIRCUIT as per MIL-STD-220A
Figure 4.13
Attenuation oj RF conducted current through 10 J-lF Jeedthrough capacitor
Reproduced by permission of Solar Electronics
~5cm~
BLOCKING INDUCTOR
..---
TEST
SAMPLE
r-'lOWER SOURCE
Xc< 5 ohms
WAVEFORM MONITOR
POWER
AMPLIFIER
Figure 4.14
500hms
OSCILLOSCOPE
OR
TUNEABLE RF
VOLTMETER
Conducted susceptibility test using RF coupling capacitor (MIL Syn 461 50 kHz-400 MHz)
Figure 4.15 Use of
coupling capacitors in
IEC801-4)· transient
injection onto power lines
33nF COUPLING CAPACITORS
TRANSIENT BURST
GENERATOR
EUT
L
N
E
INTERNAL
POWER
SUPPLY
Mains filter section
Reproduced by permission of BSI
Insulating support
REFERENCE GROUND PLANE
emissions. AIm-long coupling wire is spaced 5 cm
above the cable under test, which is itself 5 cm
above the ground plane. See Figure 4.20.
4.2.5 High-impedance RF voltage probes
It is often required to make a measurement of RF
voltage on a conductor or component without
100,uH DECOUPLING INDUCTORS
(With lossy ferrite damping)
loading the circuit to any appreciable extent so
that a true representation of the signal characteristics can be observed. This implies that any direct
connection device should have a high input
resistance and a low shunt capacitance to present
a high impedance across the frequency band of
interest. For EMC measurements, such probes
need to cover at least DC to 1 GHz if possible.
MEASUREMENT DEVICES FOR CONDUCTED EMI
57
Decoupllng network
-oI
AC(DC)
POWER
SUPPlY
I---~L....L-L-J-L---------_+_--
----__(
I
T
-0-------------------------------~
EUT
(a)
Decoupling network
OI
AC(DC)
R=10ohms
~--('(Ynl---------_+_---_+_
--___<
I
POWER
o
SUPPLY
I
O - - - I I t - - - - - - - - - - - - - - - t l I - - - - - - - - - -___
EUT
~___i!_____,._-'
I±
(b)
R = 400hms
C=O.5pF
Decoupllng network
1.5 tnH INDUCTORS
AUX.
EQUIP.
EUT
(c)
Figure 4.16
Various coupling capacitors used in IEC801-5 for transient burst injection
( a) Test set up for capacitive coupling on ACI DC lines)· line-to-line coupling) generator output floating
(b) Test set up for capacitive coupling on ACIDC lines)· line-to-ground coupling) generator output floating
or earthed
(c) Test set up for unshielded 110 lines)· line to ground coupling
Reproduced by permission of BSI
58
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
Coaxial cable, twisted pair or
multi-lead cable - screened
or unscreened
Coupling unit
I
other cables for mains, loud speakers
etc each terminated with a coupling
unit (150 ohms)
t
EQUIPMENT UNDER TEST
-- D
J
-----_--..
-----,,----....
~C1--
~
\
1
L
100 ohms
+
Wanted signal generator
or auxilary equipment
..
/
//
/
/
/
/
/
/
/
/
L = Isolation inductance
INTERFERENCE RF SIGNAL GENERATOR
C 1 & C2 capacitors with low
RF impedance
I = INTERFERENCE CURRENT
R int + R1 = 150 ohms
Figure 4.17
Coupling capacitor used for signal injection (EN55020 [BS905})
Probes are available in two types: passive and
active. Passive probes are usually built as voltage
dividers with ratios of 10: 1 or 100: 1 and can present
input resistances of greater than 1 megohm. The
physical construction of the probe and the self
capacitance of the input resistor determine the shunt
capacitance. Probes of this type are commonly used
with oscilloscopes for voltage measurements within a
limited bandwidth of around 100 MHz.
If the signal to be measured is large enough to
withstand the probe attenuation and the
bandwidth of the probe is sufficiently high, these
oscilloscope probes can be adequate for EMC
Reproduced by permission of BSI
measurements. When such probes are used to
measure susceptibility signals impressed on power
lines care must be taken to ensure that, although
the amplitude of the RF signal to be measured is
acceptable, the maximum probe input voltage is
not exceeded by the power line voltage.
Input parameters for typical passive probes can
be found in Table 4.1. Care must be taken to
establish the upper frequency limit of such probes
when used for EMC testing as they will typically
not perform satisfactorily much above 50 or
100 MHz.
Special
high-frequency
probes
(HP 85024A for example) can be obtained with
Table 4.1 Examples ofprobes suitable for use in EMC measurements
Active!
paSSIve
Probe
Division ratio Input R
P
P
P
P
P
10430A
10435A
10436A
10440A
10437A
10: 1
10: 1
10: 1
100: 1
1:1
A
A
A
A
A
A
A
85024A
1: 1
10: 1
1:1
10: 1
100: 1
10: 1
100: 1
41802A
1124A
1141A
(All equipment -
Hewlett Packard)
Shunt C
(ohms)
1M
1M
10M
10M
50
(pF)
6.5
7.5
11
2.5
1M
0.7
Compensates
for input
Max. volt
1 M, 6-9pF
1 M, 10-16pF
1 M, 18-22 pF
1M,6-14pF
450
450
450
450
Freq. range
0.3 M-3 G
1M
10M
12
10
5 Hz-100 M
DC-100M
1M
7
DC-200M
Diff. mode
1.5
15
50
10
100
200
MEASUREMENT DEVICES FOR CONDUCTED EMI
59
. - . . - - - - - - - - - - 1000 mm ----------~I
I
o
o
o
o
o
o
o
70mm
COUPLING PLATES
INSULATING SUPPORTS
~UND
~=~metre
f
.--
PLANE SHAll HAVE A MINIMUM AREA OF
EXTENDING BEYOND THE DEVICE ON ALL
SIDES BY MORE THAN O.1m
1050 mm
- - - - - - _....
(a)
EUT(2)
EUT(1)
CAPACITIVE COUPLING CLAMP
i1
i2
AC MAINS SUPPLY
AC MAINS SUPPLY
a.1m
/
Insulating support
GROUNDING CONNECTION
TO MANUFACTURERS
SPECIFICATION
Figure 4.18
TO INTERFERENCE SIGNAL GENERATOR
GROUNDING CONNECTION
TO MANUFACTURERS
SPECIFICATION
(b)
Distributed capacitance clamp for use in IEC80 1-4 susceptibility testing
( a) Construction of capacitance coupling clamp
(b) Use of the clamp for injection into control and signal cables
Reprod uced by permission of BSI
Figure 4.19 Tape or wire
distributed capacitor injection
(for HF transients IEC801-4)
THIS CONNECTION SHALL BE AS
SHORT AS POSSIBLE
AC MAINS SUPPLY
COMMUNICATIONS LINES
110 CRICUITS
PROTECTIVE EARTH
/
The coupling device shall be a conductive tape
or a metallic foil in parallel or wrapped around
as closely as possible to the cables to be tested
The coupling capacitance shall be
equivalent to that of the CLAMP
1
Reproduced by permission oCBSI
60
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
RF GROUND PLANE
10 x 15 em FOAM CHANNEL 1m long
//
CONNECTOR FOR SHORT / OPEN CIRCUIT
5mm FOAM SUPPORT FOR CABLE
Figure 4.20
Capacitive coupling wire used for cable emission measurements
an input resistance of 1 megohm and a shunt
capacitance of only 0.7 pF.
Active probes can be used to make highimpedance measurements of small m V -level RF
signals over a wider frequency range. Care must
be taken in the probe preamplifier design to
minimise distortion products (important for EMC
measurements) and to maintain a wide dynamic
range. Probes such as HP 41800A cover the
frequency range 5 Hz to 500 MHz with a unitary
transfer function and have an input impedance of
100 kohm with 3 pF shunt capacitance.
As a further example, the Anritsu MA44B active
probe has a frequency range from 10kHz to
30 MHz, a unitary transfer function and an input
impedance of 300 kohm with 20 pF. Its maximum
RF input voltage is around 0.25 V. Active
wideband probes are used mainly in low signal
level development or diagnostic testing applications where circuit boards are being examined for
sources of interference.
Some passive direct connection probes can be
used to measure the relatively large signals up to
300 V pk. from exported transients as in the ·DEF
srf AN 59-41 DCE03 test for example, see Figure
4.21a and b. They can be used to monitor the
impressed RF interference signal voltage of a few
volts RMS on power lines as in MIL STD 462
(N3) CS02. See Figure 4.22.
4.2.6 Directly connected transformers
Direct connection transformers are used in EMI
testing for:
Reproduced by permission or leT Inc.
Series injection of audio- and low-frequency
interference signals onto power lines
Measurement of low-frequency conducted
emissions on power lines
Series injection of transients into power lines
Generating several kV pulses for use with
spark gaps in discharging transients into
screened cables or structures.
Audio-frequency signals may be injected into
circuits for EMC tests such as MIL STD 462
CSO 1 using directly connected iron cored transformers. Such transformers have primary windings
with less than a 5 ohm impedance, a turns ratio of
2: 1 and a heavy-duty secondary winding capable
of carrying 50 A AC or DC. They are employed
as shown in Figure 4.23 to series inject the audio
interference signal of up to about 100 W into the
mains circuit of the EDT. In some cases an
additional secondary winding is provided which is
used to connect a meter/oscilloscope to monitor the
injected signal level.
Audio-frequency transformers can also be used
to couple low frequency conducted emissions from
power cables to an isolated measurement meter as
in Figure 4.24. For AC lines it may be necessary
to in trod uce a mains-freq uency notch filter to
prevent input overload of the EMI meter.
Spikes or transients with voltages up to around
600 V pk., such as that shown in Figure 4.25a, can
be series injected into power circuits as in Figure
4.25b using high-frequency ferrite cored' pulse transformers. Higher voltages of up to 1200 V can be
injected into 50 ohm circuits by using transformers
with a high turns ratio. Typical output winding
MEASUREMENT DEVICES FOR CONDUCTED EMI
61
AUDIO ISOLATION TRANSFORMER
I
AF.
OSCILLATOR
W
A.F.
AMPLIFIER
~
P
EQUIPMENT
UNDER
TEST
?'-~
~TEST_
~
~
DC orAC LINE
PRIMARY WINDING P < 5 ohms
FREQUENCY 30Hz 250kHz
SECONDARY POWER LINE
CURRENT 50A AC/DC
BALANCED OSCILLOSCOPE PROBES
U
I II
Figure 4.23
SECONDARY WINDING S - 10hm
POWER CAPACITY 100W
TURNS RATIO 2:1
Current injection via heavy current
iron-cored transformer
DIFFERENTIAL
~ OSCILLOSCOPE
NOTCH OR HIGH PASS
TO SUPPRESS
AC POWER LINE
FREQUENCIES
PROBES CONNECTED 50mm from EUT CONNECTOR
(a)
POWER SUPPLY
INSTRUMENTATION SUPPLY
SCREENED ROOM WALL
30,OOOuF CAPACITOR FOR DC SUPPLIES
TRANSFORMEri - - - - - -
+
LINE
--..J
::c
-=-10MF
~
V
SWITCH
NOT USED
TEST
SAMPLE
10 MF
I::UT
(b)
Figure 4.21
Direct voltage probe measurement used in
UK DEp-' STAN 59-41 DCE03
( a) Test configuration for A C supply
( b) Test method DCE03 exported spikes
on power lines
]?igure 4.24
Audio transformer used as a pick-up device
for conducted interference at audio flow
frequencies
Some EMC specifications such as MIL STD
1541 (for spacecraft hardware ) require the
injection of a high voltage transient onto the
structure of the system under test. An EHT pulse
transformer such as Solar 7115-1 can be used to
generate up to 15 kV which can then be
discharged to the structure or equipment case
being tested via a spark gap as in Figure 4.26.
Reproduced by permission of HMSO
4.3 Inductively coupled devices
{MIL·STD.461 CS02}
(N4-50kHz·400MHz)
}zgure 4.22
EMI METER
MEASURES RF CURRENT
Passive and active probes used to measure
amplitude of injected RF signal
inductance is around 300,uH. I t is possible for the
transient wave shape to be slightly degraded by
the transformer which has higher output
impedance than the spike generator.
4.3.1 Cable current probes
The most widely used inductively coupled EMC
measurement device is the cable current probe or
clamp. I t is a conveniently small device, about
5-10 cm across which is constructed in two halves
hinged together. It can be clamped around a
single conductor or cable bundle with ease. When
connected to an EMI meter, sensitive measurements as low as a few microamps of RF current
can be made. Figure 4.27 shows a typical probe
with an aperture of about 4 cm in diameter.
A circumferential magnetic field exists round
any conductor carrying the RF current to be
62
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
H FIELD AROUND THE CONDUCTOR
H
CONDUCTOR CARRYING
A CURRENT
TIME (microseconds)
CURRENT FLOWING IN
CONDUCTOR UNDER TEST
(a)
BASIC RF CURRENT PROBE
SPLIT FERRITE TOROID
CONCENTRATES H FIELD AROUND
CABLE UNDER TEST THROUGH
PICK-UP COIL
PARALLEL INJECTION ON DC LINE
SERIES INJECTION ON AC LINE
(b)
Figure 4.25
Transient injection from spike generators
with transformer outputs (a) Transient
shape with unterminated output as required
by MIL STD 462 (b) Series injection on
A Cline (left) and parallel injection on DC
line (right)
:::::; 600 V OUTPUT
TRANSFORMED UP TO :;:::,-10kv
TRANSIENT
GENERATOR
EUT
t
FERRITE CORED
HIGH FREQUENCY
TRANSFORMER
Figure 4.26
SPIKE DISCHARGE
TO EUTCASE
HF step-up transformer for spike injection
Figure 4.28
Principle of cable current probe field around
conductor
measured as. ,shown in Figure 4.28. The toroidal
ferrite core of the current probe concentrates this
flux within itself. The toroidal core is split to
allow the probe to open. The mating surfaces of
the two halves must be carefully machined and
positioned such that a low reluctance path is
maintained around the magnetic circuit of the
toroid. The permeability of the ferrite, and not
that of the air gap, must be the limiting factor
minimising the overall toroid reluctance.
The concentrated flux in the toroid induces a
vol tage in the ou tpu t winding proportional to the
permeability, cross sectional area of the ferrite
toroid and the number of turns in the output
winding.
where
Vout
kflANf I cond .
Vout
output voltage
constant
core permeability
CSA of core
number of turns
frequency
current in conductor
k
fl
A
N
f
I cond
\
CABLE UNDER TEST
Figure 4.27
PROBE OUTPUT CABLE
TO EMI METER
Typical EMGY current probe for measuring
conducted RF emissions
4.1
The RF current probe is therefore a wideband
RF transformer which uses the conductor in
which the current to be measured is flowing as
the single-turn primary winding. See Figure
4.29. Note that an electrostatic shield is included
In the construction to prevent capacitive
MEASUREMENT DEVICES FOR CONDUCTED EMI
63
OUTPUT TO COAXIAL CABLE,
50 OHMS IMPEDANCE
~ SECONDARY
V(:)
/J
POWER LINE
~~~~~~;ECAN
FERRITE CORE
====
/
~
o
50 OHM LOAD
/
PRIMARY
(TEST SAMPLE
LEAD)
\
RF CURRENT TO BE
MEASURED
1.0
~
ELECTROSTATIC
w
SHIELD (CASE)
z
«
.5
()
o
/
O---~---~---:--i(f)--I: 0
TRANSFORMED DOV'
2.0
(J)
I
w
Cl.
~OWER
~
a:
LINE AC OR DC
~C~~iN~U~:~~~GH
CONDUCTOR UNDER
TEST
I:l:
(J)
.05
z
«
a:
f-
.01
Figure 4.29
" - - _ - - A . _ " - - _ - - - & _ . a . - - _ - - - & _ " " ' - -_ _.L..--...I-o-....
.01
RF cable current probe is transformer
.05
.1
5
.5
10
50
100 200
FREQUENCY IN MEGAHERTZ
(a)
coupling between the windings and the
cond uctor under test. The performance of the
current probe may be expressed in terms of a
sensor transfer impedance:
+10 ....----....---__- - - . , - - - - - . , . - - - . . . -__- -
r-----,
+5
4.2
-5
where Vout is the voltage developed across a 50 ohm
termination on the output and I cond is the current
flowing in the conductor being measured. Typical
transfer impedances are about 1 ohm, giving
1 volt output per amp. Practical current probes
are optimised with internal loading to yield flat
transfer impedances over most of their operating
frequency range. The transfer impedance of a
typical general performance current probe
(Carnel Labs. Corporation 91550-2) [8] can be
seen in Figure 4.30a. The frequency dependence
indicated in eqn. 4.1 can be seen below 100kHz.
The upper frequency limit of a current probe
design may be determined by factors such as selfresonance and ferrite losses.
The probe transfer impedance is often expressed
in terms of dB above or below 1 ohm as in Figure
4.30b. This convenient notation allows the EMC
engineer to calculate the measured current from:
-10
-15
1 - -_ _..L.----'--_ _--L...----I"--_ _.L..--&-_ _- - I . . . - - - l L . - - - I
.01
.05
10
.5
50
100
200
FREQUENCY IN MEGAHERTZ
(b)
Figure 4.30
Transfer Junctions oj typical current probe
( a) Transfer impedance in ohms
( b) Tran~fer impedance in dB ohms
Reproduced by permission of' Camel Labs Corp.
::2:
I
o
W
z
o
~
9w
+30
co
a:
~
+20
>
~
«
fg
+10
~
w
()
The
transfer function of a more sensitive
(Z == 0 to 15 dBohm) and higher frequency
(1 MHz-1 GHz) current probe (Carnel Labs.
Corporation 94111-1) [8] can be seen in Figure
4.31.
Current probes are sensitive well-behaved
sensors which are easy to use and give repeatable
results. RF currents from microamps up to 20 A
or more can be measured. However, care must be
taken with regard to the total current (RF and
power line components) flowing in the conductor
being measured. At high combined current levels
it is possible to saturate the ferrite toroidal core
and thus change its small-signal permeability.
This results in incorrect measurement of the RF
component of the total current. Power line
z
«
o
w
Cl.
~
a:
I:l:
(J)
-10
L . -_ _--A._--'--
1
z
«
a:
10
-'-----&
50
100
-"
500
1000
FREQUENCY IN MEGAHERTZ
f-
Figure 4.31
Transfer Junctions oj HF current probe
Reproduced by permission or Camel Labs Corp.
currents of the order of 200-400 amps, depending
on power line frequency, can be accommodated
before saturation results.
Because the current probe forms a transformer
with the conductor under test as the primary
winding, a small series resistance of a fraction of
an ohm is introd uced in to the primary circuit
owing to transformation of the 50 ohm (plus any
64
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
internal probe resistance) secondary load by the
effective turns ratio of the probe. In most
measurement
situations
the
additional
transformed resistance has no effect on the
operation of the circuit under test.
Care should be exercised when current probes
are used to monitor circuits which may be
sensitive to additional resistive loading. Freerunning RF oscillators and circuits exhibi ting
spurious oscillation are examples where frequency
pulling may result from the additional loading.
The spectrum observed with the probe in such
cases may not be truly representative of that
under unloaded conditions.
Current probes are used extensively in EMC
conducted emission testing to military specifications such as MIL STD 462 and DEF STAN 5941. Their use is less evident in EMC standards
relating to testing of commercial electronic
equipment where the LISN method currently
predominates.
A current probe will measure the sum of all
currents flowing in a cable bundle, or the screen
curren t in the case of a screened cable, see Figure
4.32a. If the probe is placed around one
conductor in a bundle with another conductor
close by, then although the probe construction
offers considerable rejection of unwanted signals,
it may not measure just the current flowing in the
cable under test, see Figure 4.32b. In such cases
the cond uc tors should be separated a few
centimetres if possible and any changes in the
measured current noted.
During development testing it may be advantageous to determine not only the magnitude but
also the nature of the interference current flowing
in a set of conductors to learn something about
the probable source of the interference. The differential mode current can best be measured as
shown in Figure 4.32c and the common-mode
current as shown in Figure 4.32d.
The RF current in a cable will usually exhibit
standing wave patterns along its length. In
conducted emission EMC tests this phenomenon
iSCREEN
CURRENT
DIFFERENTIAL
COMMON MODE
MODE
..
(a)
(b)
i DIFFERENTIAL
MODE
CURRENT
(c)
F'igure 4.32
Making cable current measurements with a current probe
( a) Measuring shielded cable screen current
( b) Measuring of common Idifferential mode
( c) Maximising differential mode pickup
( d) Maximising common mode pickup
Reproduced by permission of' leT Inc.
i COMMON MODE
CURRENT
( d)
MEASUREMENT DEVICES FOR CONDUCTED EMI
TEST DCE01
POWER SUPPLY
MEASURING SET
SCREENED ROOM WALL
65
compared against the limits. The conducted
emission limits for these two tests (for military land
systems EUTs) are shown in Figure 4.34a as
examples of the levels of conducted RF current
which can be measured with toroidal current probes.
30,OOOjJF CAPACITOR FOR DC SUPPLIES
4.3.2 Current injection probes
EUT
GROUND PLANE
(a)
TEST DCE02
POWER SUPPLY
MEASURING SET
SCREENED ROOM WALL
EUT
EUT
50Q
GROUND PLANE
(b)
Fzgure 4.33
Positioning of RF current probes on power
and signal cables in UK DEF STAN 59-41
tests
Reproduced by permission of HMSO
IS
only important when measuring VHF
frequencies on cable longer than a few metres.
The position and amplitude of RF current
maxima and minima can be explored by moving
the probe along the cable. In some EMC
standards that call for the use of current probes,
their position along the cable is specified with
regard to the distance from the cable connectors
on the EUT. In the DEF STAN 59-41 DCE01
test this is 5 cm from the LISN connection on the
power lead. See Figure 4.33a. For the DCE02 test
(see Figure 4.33b) with leads longer than 1 m and
for frequencies above 30 MHz the probe is
positioned 5 cm from the connectors at both ends of
the cable and the greatest emission levels are
Specially designed low-loss current probes can
be used to inject RF current into cables.
Formal EMC tests using this technique are a
recen t introd uction and have been pioneered in
the
UK
primarily
for
testing
military
equipment. However, the technique can also be
used for the developmen t testing of commercial
electronics.
The transformer action of a toroidal current
probe is exploited to produce a current injection
test for cables which does not require direct
connection to the circuits being tested. This
makes the tests quicker and potentially more
representative of the functioning system with an
undisturbed
electromagnetic
topology.
An
example of the use of injection probes is that
called for in the clearance 'of military aircraft
under RAE technical memorandum FS510 [9J.
The current probe injection test is now included
in DEF STAN 59-41 as DCS02 for power,
con trol and signal leads over the frequency range
50 kHz-400 MHz.
The precise test method is complex and the
reader should refer to the appropriate reference
for a full understanding. The construction and
performance of the injection probe will be
considered here as representative of this type of
EMC test device. A low-loss high-power current
injection probe design capable of handling 200 W
input RF power was produced initially by ERA
Technology in the UK and designated ERA36A
and ERA37A. The Carnel Labs. Corporation
company in the USA has produced an equivalent
injection probe designated model 95242-1. The
characteristics of this probe are given in Table 4.2.
The probe has been designed to handle high
input RF power and has more core material and
smaller core gaps than the general emission
measurement probes. The low insertion loss of
about 5 dB (see Figure 4.35a) over most of the
freq uency range also ~akes the device an
extremely sensitive emission measurement probe
with a transfer impedance as high as +40 dB
ohm. See Figure 4.35b.
In the injection mode the probe is used with a
200 W amplifier and a directional coupler to
measure the forward power to the probe. This is
necessary because when fixed around a bunch of
conductors with unknown RF impedance, the
probe can present a poor VSWR to the amplifier.
66
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
Figure 4.34 Typical test
limits for conducted
current as measured with
current probe
TEST METHOD DCE01/2
~
LIMITS FOR LAND SYSTEMS
y-----.,..-----...,.--------------,..-----...,.------
140
120
2-
co
~
z
w
a:
gs
100
80
U
z
@
60
(J)
~
w
o
w
100 MHz, 40
40
~---------...... CLASS 0
I-
U
:::>
o
z
100 MHz, 25
~--------...... CLASSC
20
100 MHz, 10
ou
~------... CLASS B
o
-20
Reproduced by permission or HMSO
2 MHz, 0,..----10-0-M-H-z,-0-t CLASS A and E
""-100
1kHz
As a check on the RF current being induced into
the cable a measurement current probe is placed
5 cm from the connector of the EDT and the
injection probe as in Figure 4.36.
4.3.3 Close magnetic field probes
RF pickup devices that could be considered as
small magnetic field an tennas have been
included in the section on inductively coupled
Table 4.2 High power current injection probe
Specifications model 95242-1
Frequency range
2-400 MHz
Window diameter
40 mm
Outside dimensions
102 x 130 x 60 mm
Weight
1.60 kg
Input connector
Type N
Maximum input power
200 W
Maximum core temperature 80°C
Recommended maximum
35°C
tempera ture rise
Maximum time for
30 min.
continuous rating at full
power
Turns ratio
1: 1
Inductance
0.8,uH, ±20 0/0
Self-resonan t frequency
350 MHz, ±10 0/0
Impedance at resonance:
unloaded
76 + jO ohms
95241-1 calibrations jig
50 + jO ohms, ±5 %
Frequency 2 5 10 20 50 100 200 300 350 400
(MHz)
Insertion 17 9.5 6.5 6.5 5 5
5
5 5.5 6
loss (dB)
"""'10kHz
100kHz
1MHz
"""--
__
10MHz
100MHz
devices as they operate at frequencies up to
1 GHz and at a distance of only a few mm from
the curren t carrying conductor. Thus they
operate in the near field, and with the probe
elemen ts being small loops, the predominan t
coupling is inductive.
Small probes or wands as they are sometimes
referred to, are an important tool for diagnostic
and development testing at board and box level.
I t is possible to make a set of probes covering
various frequency ranges and to calibrate them
sufficient for nonconformance test purposes.
Proprietory equipment employing dual pickup
loops and a balun can be obtained such as
HPl1940A/11941A. These probes have calibrated
transfer functions to yi~ld the absolute magnetic
field st~ength in dB,uA/m from the EMI meter
readings in dB,uV. For example, from 9 kHz to
30 MHz with probe HPl1941A and 30 MHz to
1 GHz with HPl1940A [10].
Close-in probes can be used for tracking down
sources of RF emission from components, circuit
boards, apertures in equipment boxes and leakage
from connectors and screened cables. When
connected to a spectrum analyser that can rapidly
sweep over wide bandwidths to reveal the
amplitude of components of complex signals, the
EMC engineer has a powerful diagnostic tool.
4.3.4 Surface current probes
These small inductively coupled sensors are
designed to measure the RF current flowing in a
particular direction on a conducting surface. The
unit is a proximity RF current transformer where
the surface on which the insulated device sits forms
the primary circuit. The probe is placed with its
MEASUREMENT DEVICES FOR CONDUCTED EMI
Figure 4.35 Performance
characteristic of typical
current injection probe
20
\
18
\
\ \
\ \
\ ~
16
CO
"0
14
~
en
en
0-J
Z
0
i=
a:
w
en
~
\
12
10
\
\
67
:\
:\
\
8
~
'"
"....-.---,
----------
'-'-
6
...................
"
4
,~
"""'----
.",/
--------------_ ......
.,;
,
2
0
1
2
10
5
(a)
20
50
100
200 300 400500
FREQUENCY IN MHz
Injection Probe Model 95242-1
50
en
~
:r:
20
0
~
w
z
10
w
a.
~
5
()
«
0
a:
w
LL
C/)
Z
«
a:
.-
2
2
(b)
5
10
20
50
FREQUENCY IN MHz
insulated base against the conducting surface in
which the RF current is flowing, as in Figure 4.37,
and is orientated to obtain the maximum response
on the EMI meter to which it is connected.
The RF current flowing in the test surface
beneath the effective area of the probe is obtained
by dividing the measured EMI voltage by the
transfer impedance of the probe in ohms, in the
same manner as for a cable current probe.' See
Figure 4.38 for the transfer impedance of typical
devices such as Fischer probes [11] model
numbers F-91 and F-92.
The total RF current flowing in a surface can be
100
200
500
Reproduced by permission o[ Camel Labs Corp.
measured by dividing the surface into probe
footprint segments along a line normal to the
direction of current flow and summing the
measurement made at each segment.
These probes operate over a frequency range
from around a hundred kHz up to a few hundred
MHz and can be used to measure the skin currents
which are set up on system structures such as cable
trunking, equipment racks or mainframe computer
cabinets when illuminated by electromagnetic
radiation. They are also useful in determining the
distribution of interference ground currents within
systems such as military vehicles and spacecraft.
68
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
Figure 4.36 Current injection
and measurement probes
used together to stimulate
cable to a known level
TEST
SAMPLE
AMPLIFIER
SIGNAL
GENERATOR
DIRECTIONAL COUPLER
FORWARD POWER
/TO PROBE
___ INJECTION PROBE
Injection currents controlled
to give known/wanted
measured current levels in
the cable under test
Reproduced by permission of HMSO
4.3.5 Cable RF current clamps
In his survey of EMC measurement techniques
Jackson [1] gives a brief history of the
development of the cable current clamp from
initial experiments in Sweden. Experiments were
carried out to enable radiated field measurements
to be made in a laboratory by using a movable
coaxial filter on the mains lead of an EDT to
maximise the radiation from the equipment.
Further work by the Swiss PTT laboratories led
to the use of ferrite rings, and this evolved into
the ferrite cable clamp.
For a full history of the development of this
probe consult the reference given in CISPR
publication 16, Appendix S. The probe specified
in CISPR 16 was conceived in 1966 for use in
radiated emission testing in an attempt to obtain
better agreement between measurement results
and operational experience.
The use of the clamp requires the position of the
Surface current probe is orientated for
maximum pick-up
Produce records of
power meter readings
for given measured
cable current values
Cable into which current is being
injected presents variable
impedance to injection probe
leading to VSWR variations
EMI
METER
MEASUREMENT
CURRENT PROBE
RF
POWER
METER
absorbing element to be adjusted along the length
of the mains input cable to an EDT. The
im pedance discon tin ui ty represented by the
absorbing clamp on the single-wire transmission
FISCHER PROBE
model no. F·91
-10 - - - - - - - - - . - - - - - - - - . . - - - - - - - - , . - - - - .
~
I
0
T""
UJ
>
0
CD
«
-20
.0
"0
UJ
0
Z
/
«
0
UJ
a..
~
-30
0:
UJ
lL
(f)
Z
«a:
I-
-40
1MHz
10MHz
100MHz
FREQUENCY
FISCHER PROBE
B FIELD
~
model no. F-92
+10
I
0
T""
UJ
>
0
CD
«
.c
"0
UJ
0
Z
«
0
UJ
a..
~
0:
UJ
-10
lL
(f)
Z
«
a:
I-
1MHz
10MHz
100MHz
1000MHz
FREQUENCY
Figure 4.38
Figure 4.37
Using surface current probe
Reprod uced by permission of' ICT I ne.
Transfer impedance oj surface current
probes
Reproduced by permission of Fischer Custom Coms.Inc.
MEASUREMENT DEVICES FOR CONDUCTED EMI
Typical exanlple
Figure 4.39 Use oj
absorbing clamp Jor
measurement of
interference power
30 MHz-300 MHz
MOVEABLE CLAMP
d
A
~
\..--f=E::::::::t--_H_---l
69
F
~1-B---t-C-+--F=D=f----EtG-J-----B-II-_~~~~~~-E,t=:==:::1...;;.;;.;;;..;\~-~Q:
1----\--When
L~4.2m,
F min ~ 40MHz
FIXED
ABSORBER
CABLE UNDER TEST
DETAILS OF ABSORBING CLAMP
SINGLE TURN
SHIELDED CURRENT PROBE
MEASUREMENT CABLE
ABSORBER RINGS
/
---,..........,.-------~-----E~~~~~~~}~-~i-+-H--,.~1~-:
d
EUT
60rl~~~_____
METER
~~5.f8~
l=1~~r=:H:~t:=+~~I:::::::l------===RRRR_=Jf
--~12-18==m~
0 EfEjEj~ TO
::---t=:rF=:rt==:t-,.---r:==n:==n:==n==nF=rl::=:r1F=r_==--:.=-=-:.=
3
r~gs
U
56 r?ngs
CABLE
UNDER TEST
\
B
ABSORBING
FERRITE CLAMP
line, causes the line impedance presented to the
in terference source to change in such a way that
the maximum RF power is transferred to the
associated measurement probe. In this way, a
measurement can be made at each interference
frequency which represents the maximum possible
power which can be radiated by the equipment
and its cable.
The construction of the clamp is shown in
Figure 4.39. The key measurement component of
the clamp is the Faraday loop of coaxial cable
which is wound around three ferrite rings,
labelled C in the diagram. This acts as a toroidal
current probe and produces an output voltage
proportional to the RF current flowing on the
cable under test. Further along the cable from the
EUT which generates the interference emission,
are anum ber of lossy ferrite rings which act to
absorb the interference signal once it is past the
current probe. The assembly is moved up and
down the cable under test to obtain maximum
readings at each frequency of interest. Other
ferrite rings are placed around the measurement
coaxial cable from the current probe to absorb
any spurious signal pickup on the shield.
The measurement of RF power available to be
radiated from the cable under test at each
frequency of interest is made by a substitution
method where the signal reading from the EMI
MAINS
Reproduced by permission of BSI
meter is compared with that obtained during a
calibration of the clamp in a special jig and
recorded on a calibration chart. The chart is a
record of the clamp insertion loss as a function of
frequency from 30 to 300 MHz. Details of the
current clamp and the calibration method can be
found in EN55014/BS800 and VDE0875.
The probe- may ,give readings which correlate
well with everyday experience of radiated interference from typical commercial equipment, but it is
time consuming to have to adjust the position of
the probe along the line to obtain a luaximum
signal reading at every frequency of interest in an
emission spectrum. The need to physically move
the probe means that it is very difficult to
automate the process in order to speed up the
measurement.
The absorbing clamp method, although widely
used
for
testing
commercial
electronic
equipment, is not without its critics. Kwan [12]
presents a keen analysis of the drawbacks of the
method and suggests how the device may be
improved by separating the current probe and
the mismatch/absorption unit so that they can be
moved a part as necessary, to ensure that the
absolute maximum energy transfer to the probe
is obtained.
An idea of the interference RF power levels that
can be measured with the absorbing clamp
70
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
Table 4.3 Typical interference levels on cables that can be measured using absorbing clamp device (EN55014)
Frequency
range
Household and
similar appliances
Portable tools: rated power of motor
~700W
700-1000 W
1000-2000W
MHz
dB (pW) dB (pW)
quasipeak average*
dB (pW) dB (pW)
quasipeak average*
dB (pW) dB (pW)
quasipeak average*
dB (pW) dB (pW)
quasipeak average*
30 to 300
Increasing linearly
with the frequency
from
45 to 55
35 to 45
Increasing linearly
with the frequency
from
45 to 55
35 to 45
Increasing linearly
with the frequency
from
49 to 59
39 to 49
Increasing linearly
with the frequency
from
55 to 65
45 to 55
* If the average limit is met when using a quasipeak detector receiver, the test unit shall be deemed to meet both limits
and measurements with the average detector receiver need not be carried out.
CABLE UNDER TEST
(not power cables)
MIL STD 462CS 06
\
BOX INDUCTION WINDING
EUT
or
LOAD
CABLE INDUCTION WINDING
TRANSIENT SOURCE
POWER LINE FREQUENCY SOURCE
>
o
o
AC POWER MAINS
VARIAC
Figure 4. 40
Magnetic induction tests using simple wire
coils on boxes and cables
method can be seen in Table 4.3. This shows the
limits set out in EN55014 for the interference
which is tolerable from household appliances and
portable power tools. Levels of around 35 to
50 dB PWare specified when measured using an
average and quasi peak detector.
4.3.6 Magnetic induction tests
The susceptibility of boxes of electronics and
attached cables to magnetic induction fields at
very low frequencies can be determined by
generating fields from nearby wires or coils
carrying heavy current at the power line
frequencies. Such tests are specified in MIL
STD 462 (RS02) and call for heavy-duty wires to
be wound around the interface signal or control
cable under test in a spiral with a pitch of two
turns per metre. See Figure 4.40 for the layout of
the induction cable. A current of 20 amps is
passed through the wire at the power line
frequency appropriate to the unit under test
(usually 50, 60 or 400 Hz). The field produced
around the induction cable is closely coupled to
the cable under test and the coupled power line
interference signal enters the EDT via the cable
connectors. EDT power line cables are exempt
from this test.
Signal cables are to be tested in bundles or
groups. However, White [13] questions the
validity of spiralling the test wire around the
cable to be tested. He suggests laying the wire
along side and parallel to, the cable under test to
maximise the induced voltage in any cable pair
in the harness being subjected to the induction
field.
A very similar power line ind uction field test is
carried out on the EDT itself by wrapping the
wire around the eq uipmen t case at a pitch
separa tion of 30 cm over the heigh t of the box
and applying the 20 A current. See Figure 4.40.
Spikes or transients which are produced from
the generator detailed in test CS06 of MIL STD
462 are also fed into the same induction cable
wrapped around both the box and interface
cables, to perform transient pulse tests. The
correct applied stimulus level is obtained by
setting the spike genera tor ou tpu t to 100 V
measured across a 5 ohm load.
4.4 References
JACKSON, G.A.: 'Survey of EMC measurement
techniques', Electr. Commun. Eng. ]., March/April
1989
2 'Radio interference measuring apparatus and
measurement methods'. CISPR 16
3 MIL STD 462 Notice 3, 1970, pp. 21-23
4 'Instruments, components and accessories for the RFI/
EMC engineer'. Solar Electronics Co., 901 North
Highland Avenue, Hollywood, CA 90038, USA
MEASUREMENT DEVICES FOR CONDUCTED EMI
5 Draft BS6667, 1990: Electromagnetic compatibility
for industrial process measurement and control
equipment, Part 5: surge immunity requirements
6 BORESERO, M., VIZIO, G. and NANO, E.: 'A
critical analysis of the immunity methods for
and
television
broadcast
receivers'.
sound
Proceedings of lEE symposium on EMC, UK,
1990, pp. 219-226
7 'A two-part five-day comprehensive training course
in EMC' part 2. Don White Consultants, PO Box
D, Gainesville, Virginia 22065, USA, page 2.1.28
8 'Calibration & operation manuals for Carnel Labs.
Corporation current probes 91550-2 and 941 f 1-1'.
Carnel Labs. Corporation, 21434 Osborne St.,
Canoga Park, California, 91304-1520, USA
71
9 'Recommended test specification for the electromagnetic compatibility of aircraft equipment'. Technical
memorandum FS(F)510, RAE Farnborough,
Hants, UK
10 1990 product guide. Hewlett Packard, p. 128
11 'Fischer surface current probes'. Fischer Custom
Communications, Box 581, Manhattan Beach, CA
90266, USA
12 KWAN, H.K.: 'A theory of operation of the CISPR
absorbing' clamp'. Proceedings of lEE symposium
on EMC, 1988, pp. 141-143
13 'A two-part five-day comprehensive traInIng
course in EMC' part 2. Don White Consultants,
PO Box D, Gainesville, Virginia 22065, USA,
page 2.2.23
Chapter 5
Introduction to antennas
EMC antennas
In the following chapters, antennas that are
commonly used in EMC radiated emission and
susceptibility testing are examined individually in
detail. Particular characteristics are explored and
reference made to tests that employ the various
types of antenna.
EMC measurements can be complex and
inherently unrepeatable. This is particularly true
when Hlaking radiated emission or susceptibility
measurements in anything other than ideal freespace test conditions. Military EMC standards
require measurement to be made in
chambers which mayor may not have
radio absorbent material (RAM) to damp out
wave reflections; if uncontrolled
an increase in measurement
5.2 EMC antenna basics
5.2.1 Arbitrary antennas
Consider the impact of an electromagnetic wave
shown in Figure 5.1, which is defined by E) l!
(wavefield
impedance),
wavefront
phase
curvature and the direction of the wave normal k,
which is incident on an arbitrary conducting
surface S from which power can be extracted to a
load Z. A linear transfer factor can be established
for the voltage delivered to the load in terms of
the incident wavefield. This factor is a function of
all the specific conditions under which it was
obtained. It depends on the detailed nature of the
tests on large items of equipment
may have to be made on an open range in the
presence of ambient electromagnetic noise, an
uncertain ground plane and possible reflections
from
objects. All these effects can increase
measurement uncertainty. Standards covering
radiated emission testing of commercial electronic
and
particularly
information
usually specify testing on a
type of open test site that has to be
calibrated before use. Repeatability of
test results measured on an open range is however
also open to question and continues to stimulate
debate in the EMC community. See Chapter 3
References 11, 12, 15-17 and 19.
Whether the radiated emission testing is carried
out in screened rooms or on an open field test site
an tennas used are the
componen ts in the
measurement chain. What these various antennas
measure, and the influence that surroundhave on these measurements, is often not
and can lead to considerable
and error.
antenna theory is complex and
mathematical and much has been written
on the basic
of antennas [1-4] and the
of many
antennas for communications use from HI" to millimetric wavelengths
7]. It is neither possible nor appropriate to cover
such
in detail in this text on EM C
measurement, therefore emphasis is placed on the
aspects of antenna characteristics which
engineers and test technicians can use with
view to minimising potential measurement errors.
An overview of the important basic characteristics of antennas is presented to establish a
framework of
equations within which
an tenna types may be discussed further.
E vim
INCIDENT
WAVEFIELD
\
Wave
Zw
Holm
If
(is
SURFACE CURRENTS INDUCED BY
INCIDENT WAVE
RF POWER EXTRACTION
V
TECHNIQUE
....-----1]
LOAD Z
VOLTAGE DEVELOPED
POWER DELIVERED
impE~dorlce I
=V
S (x, y, z)
POWER IN WAVEFIELD
Pw Ex H W/M2
\
ARBITRARY 3D CONDUCTING SURFACE
( IN REAL ANTENNAS THE STRUCTURE IS
CHOSEN TO HAVE SPECIFIC PROPERTIES)
(aj
"YV'l11C'11Y\rl .c>Y'C'i-"l' Y\r-41Y\r<'
Ev/m
......... A.''-''--'".L 'J'L.L.LL"-.':;".L.L'--'L.L'--'
diameter d
Holm
\
Small gap
t-JA. '--""",',.L'--'L-l,.L
BALANCED MATCHED
TRANSMISSION LINE
\
DIPOLE CONDUCTING ELEMENTS
(bj
5.1
72
P
Arbitrary antenna and simple dipole
( aj Arbitrary antenna concept
( bj Simple nonarbitrary antenna - dipole
INTRODUCI'ION TO ANTENNAS
electromagnetic wavefield mentioned earlier and
on the exact form of the conducting surface, the
way the power is extracted from it and the
complex impedance of the load. The transfer
factor is meaningful only for this specific situation
and is not applicable to any other general
situation where the wavefield is different, the
conducting surface is different, or the geometrical
relationship between the two has changed.
A particular conducting surface or antenna (S)
wi th its specific transfer factor may have been
designed to be exactly what is required to meet a
particular need, say for a communications link.
But it may be of little use as a general
measurement antenna for EMC work which must
be wideband, inexpensive, portable and can yield
an absolute measurement of field strength via a
calibration curve of its transfer factor which has
been derived under controlled conditions.
73
Table 5.1 Radiation fields from Hertzian dipole
If the current in the Hertzian dipole is
1
10 cos OJt, the radiated electric field intensi ty
E and magnetic field intensity H are given in
SI units by
E
i e [60n 10 dl sin e sin (OJt - 2nrjA)JjAr
H == i¢ [10 dl sin e sin (OJt - 2nr jA) Jj2Ar
where r is the distance from the centre of the dipole
to the field point (r, e, ¢) and i e and i¢ are unit
vectors, respectively, in the directions of increasing
e and ¢. The electric vector E is proportional to
sin e and the field radiation pattern of the dipole
consists simply of a plot of sin e against e.
OJ
== angular frequency of driving current
2nf
f == frequency
A wavelength of radiation
dl == elemental length of Hertzian dipole
5.2.2 EMC antennas
The nature of antennas used In EMC measurements is quite different from those required for
specific functions such as communications. The
optimum design of EMC test antennas has
received relatively little academic attention to
date. The design aim for an EMC antenna is to
produce a simple, cheap, rugged, wideband
conducting structure that is coupled to a given
load impedance such that the output voltage can
be related simply to the E (electric) or H
(magnetic) field strength in a known manner
under general conditions of use.
Ideally, the transfer factor, or antenna factor,
should be calculable directly from a knowledge of
the geometry of the conducting surfaces, as in the
case of special D-dot antennas [8J so that an
abs9lute measurement of field strength can be
made. If this is not possible, the antenna factor
should be derivable from a simple set of measurements using known wavefields to yield a reliable
calibration curve.
There are some simple antenna configurations
for which solutions of the induced current and
voltage may be calculated for a specified
excitation [9J. Equally, the E and H fields
produced by the antenna for a given current
excitation can also be calculated. The best known
of these is that for the electrically short Hertzian
dipole and an oscillatory excitation current. For
example Benumof [1 OJ gives the formulas in
Table 5.1 for the E and H fields from a dipole
given an excitation of the form
1 == 10 cos OJt
5.1
where 1 is the time-varying driving current, 10 is the
peak driving current, and OJ is the angular frequency.
I t is possible therefore to understand how a
simple nonarbitrary conducting structure such as
a short dipole behaves, and to use this knowledge
to interpret the wavefield it will generate from a
given driving current. I t is also possible to
calculate the reciprocal behaviour of the dipole
output voltage in terms of the incident electromagnetic wavefield which is to be measured.
5.3 Basic antenna paratneters
5.3.1 Gain
Gain is a measure of the ability of an antenna by
virtue of its specific conducting structure to
concen tra te a transmitted (radiated) signal in one
direction, or to receive a signal from only one
direction, as opposed to all other directions [11 J.
Gain is usually expressed in dB relative to a
perfect isotropic radiator.
Consider Figure 5.2 where two antennas, one
isotropic and one with gain, both radiate into a
surface at a point P at distance R to deliver a unit
power density P d (watts/square metre):
An tenna gain
Thus
input power to isotropic
antenna for unit power density at P
input power to directive
antenna for unit power density at P
Pin (W) X
where W == power in watts.
isotropic source,
4nR2
gain
5.2
Note that for an
5.3
74
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
ANTENNA SYSTEM
CASE 1 - ISOTROPIC DEVICE
CASE 2 - DIRECTIVE DEVICE
E
H
Lk
-T~-+---t/
CASE 1 - P in W (ISOTROPIC)
CASE 2 - Pin W (DIRECTIVE)
POWER DENSITY ON
SURFACE = P d W/M 2
P in (DIRECTIVE) < P in (ISOTROPIC)
of the antenna. For example the physical frontal
area of a horn or parabolic dish antenna is related
to the energy capture aperture. The two are not
equal owing to the way in which the electromagnetic fields are distributed nonuniformly over the
physical area.
The gain of an antenna with a given physical
aperture is dependent on the wavelength of the
radiation being transmitted or received. The relationship between the aperture as defined by eqn.
5.8 and gain is also dependent on wavelength:
4n
gain G
DIRECTIVE ANTENNA GAIN = P in (ISOTROPIC) (for a given P d )
P in (DIRECTIVE)
Figure 5.2
where <0 is impedance offree space 377 ohms, and
E is the magnitude of the wave electric field at a
distance R. To produce a 1 Vim field at 1 m from
an isotropic antenna an input power of 33 m W is
required. For 100V/m a power of 330W is
needed. Also
5.5
where H is the magnitude of the wave magnetic
field. Thus to produce 1 A/m at 1 m a power of
4800 W is required.
For a directive antenna,
4nR E
Pin
and
P
5.4
2
Pin
<0
gain
2
2
4nR H
<0
gaIn
X
aperture
4n
5.10
5.11
4n<0
These relationships can be used to derive both the
transmitting and receiving antenna factors.
5.3.3 Transmitting antenna factor
Consider a feeder cable delivering a power P t to an
antenna. The voltage Von the line of impedance <
is given by
=
V2
Z
5.12
From eqns. 5.6 and 5.12
V2
5.7
Consider an antenna in an incident field with a
power density of P d watts/square metre which
delivers a power P watts to a matched load. Then
Pd
5.9
5.6
5.3.2 Aperture
==
A2 C x P
== - - - -d
PI
The Lorenz reciprocity theorem [1 OJ shows that
the gain figure for a transmitting antenna is the
same as that for the identical receiving antenna.
However, to better understand the concept of
receive gain it is necessary to introduce the idea of
antenna aperture.
P
A2
or
2
X
aperture
where A is the wavelength. Using eqns. 5.8 and 5.9
the received power P can now be expressed as
Concept oj antenna gain
and
X
5.8
and the aperture has the dimensions of area. The
aperture is not identical with the physical
antenna area, nor its projected area onto a plane
normal to the incident wave direction. In some
cases it can be identified with the physical shape
<
4nR 2 E 2
<0
X
gain
therefore
5.13
The ratio E / V is called the transmISSIon antenna
factor (T AF) and relates the field strength E
(V/m) produced by the antenna at a distance R
metres with an input signal of voltage V across a
line of impedance < ohms. This relationship is
useful in calculating the field strength incident on
an equipment at a distance from a transmitting
antenna in a radiated susceptibility test.
5.3.4 Receiving antenna factor
Bennett [12J states that 'antenna factors are widely
used, yet the literature does not appear to include
any detailed mathematical characterisations of
such factors', and proceeds to develop useful
formulas for some standard dipole antennas.
INTRODUCTION TO ANTENNAS
In general, the receIvIng antenna factor is
defined as EjV where E is the magnitude of the
electric field of the incident wave and V is the
voltage delivered from the antenna to the load of
impedance Z. It can be shown that
~ = ~ [z :~oainr
5.14
Knowledge of the derivation of these two antenna
factors is most important to the EMC engineer as
it permits the setting up of experiments to
calibrate antennas and derive the factors with
confidence. Otherwise the engineer has to rely on
the manufacturer's data supplied with proprietary
equipment which may contain artifacts of possibly
imperfect calibration procedures. Manufacturer's
antenna factors are usually reliable and available
in graphical form as a function of frequency.
Examples for specific antennas are shown later.
characteristics of the antenna and the relationships involving gain and distance which describe
the coupling between the antennas will no longer
rigidly apply. The antenna radiation pattern,
antenna factor and feed point impedance will
depart from calibrated values and any measuremen ts then made will be subject to an increased
uncertainty.
Consider two identical antennas separated by a
distance d in Figure 5.3a. There will be a mutual
impedance term Zm introduced into the
equivalent circuits of the two antennas as shown
in Figure 5.3b. The mutual impedance of simple
antennas can be calculated from the antenna
dimensions and spacing and may be found in
standard texts. The circuit equations relating to
Figure 5.3b are
lout (Zout
5.3.5 Antenna phase centre
GENERATOR
When an antenna is radiating into free space, the
wavefront at great distance (in the far field) is
usually assumed to be plane. This is however
alvvays an approximation as the radiation is
emitted from a structure with a finite size and so
the wavefront will have a slight curvature at a
finite distance. The apparent centre of the
curvature is usually situated on the antenna
structure and is called the phase centre.
When making calculations or measurements
which involve the distance from an antenna to an
object, the distance from the phase centre should
always be used. This can be important when such
distances are comparable with the antenna
dimensions, as in the case of some EMC radiated
emission measurements where the EDT to
antenna separation is only 1 m and the antenna is
about half-a-metre long. The position of the phase
centre on most antennas is obvious, for example
at the feed point of a dipole, but for some
frequency independent antennas such as log
periodics and log spirals the phase centre will
move along the axis of the antenna with
freq uency. This can lead to measurement errors
and even calibration errors at VHF jDHF when
the two-antenna method is used for such antennas
with a short 1 m separation.
When operating an antenna close to another
similar antenna, ground plane, earth or screened
room wall, undesirable mutual coupling will take
place between the antennas, or between the
antenna and its electrical image in any reflection.
Such an effect will alter the normally calibrated
MID - PLANE
I
I
+ Za)
RECEIVER
I
I
I
I
I
I
I
V out
lout
Zout
rdr
I
(a)
Zm
lout
Zm
19
ANTENNA I LOAD
(b)
Figure 5.3
5.3.6 Mutual ante11na coupling
75
Antenna mutual impedance coupling
( a) Identical antennas separated by d
( b) Equivalent circuit
Zg == generator impedance
Za == antenna impedance
Zm == mutual coupling impedance
Zout == load impedance
Ig == generator current
lout == load current
76
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
10,000...-------------------.....,
which leads to
--Induction f i e l d - - - - - F a r field----I
lout = Zm- (Zout
+ ZaJ
(Zg
5.15
+ Za)
<m
3000
<m
As the separation d becomes large the value of
tends to zero and the current flowing in the
receiving antenna lout as a result of mutual
impedance coupling tends to zero. The coupling
between the two antennas then reverts to only
radiative coupling which is determined by the
normal gain equations given earlier.
The problem of mutual coupling between
an tennas and their images in the earth and other
ground planes bedevils EMC measurements and
gives rise to much comment [13-18]. This subject
is discussed again later in the text concerned with
open range and screened room radiative testing.
5.3.7 Wavefield impedance
5.16
Plane-polarised wave
The wavefield impedance close to a source of electromagnetic radiation is determined by the nature
of the source. For example, for an electric-field
source such as a small dipole oscillating charge,
the wave impedance close to the source will be
high at several thousand ohms, as E is much
greater than H. For a small electrostatically
screened oscilIa ting current loop (with minim urn
exposed voltages) the magnetic field component
predominates and the ratio of EIH is low,
therefore the wavefield impedance is low, perhaps
only a few tens of ohms close to the source.
I t is useful to define the distance from an EM
source in terms of the wavelength being radiated
Ea and H<j>U+
I
(J)
E
'§
Zo = 120 1t = 377
300
n
3=
N
ZE = Zo
100
v'd2+1
--d--
ZH = Zo d
Jd 2 + 1
Zo
= 1201t =
377n
104----------+------------'
10
1.0
0.1
DISTANCE FROM SOURCE d (increments of r = _A_)
21t
Figure 5.5
EV/m
HA/m
v
Figure 5.4
I
30
A simple representation of a sinusoidally varying
electromagnetic wave is shown in Figure 5.4. The
electric field E V 1m and the magnetic field
components H Aim are orthogonal and the wave
propagation velocity is v m/s. In a vacuum
v == c == 2.9979 X 10 8 , normally approximated to
3 X 10 8 m/s. The wave impedance
<ohms
1000
Variation of waveJield impedance with
distance from source
and not as an absolute distance in metres. A
graph of wavefield impedance as a function of
distance from the source in terms of wavelength,
for both an electric and magnetic oscillator, can
be seen in Figure 5.5. Note that close to the
source, that is at distances of less than )"/2n, both
the E- and H-fields vary rapidly as square and
cubic terms with distance. Beyond this distance
the wavefield impedance from either type of
source tends to the same constant value of 377
ohms or 120n. This is known as the free-space
wave impedance which occurs in what is called
the 'far field' of the source.
5.3.8 Near-field/far-field boundary
An understanding of the origin of the Inverse
linear, quadratic and cubic dependence of field
strength with distance can be obtained by
considering the elemental dipole in Figure 5.6,
which is of length h and carries a uniform sinusoidally oscillating current of the form
I
==
10 exp (jwt)
5.17
The solution of Maxwell's equations for this
antenna element [9J leads to the components for
the electric and magnetic fields shown in Table 5.2.
INTRODUCTION TO ANTENNAS
z
Table 5.2 Solution ,[or field components for short dipole
H$
Efl
Er
p
H¢
CP-+1).
r
r
1h
0
==-
2
4n
Er
OSCILLATING
DIPOLE
CHARGE
~
E()
...---------t----y
,
I
'"
I
"
I
I
' .... ,
"
I
'" ......I
Figure 5.6
77
Oscillating dipole element
Eq ua tion 5.19 for the radial electric field E r has
only two terms in 1/ r2 and 1/ r3 . This means that
E r decays rapidly with distance from the
oscillating element and is therefore only
importan t close to it. The 1/ r3 term can be
identified with the field calculated for an electrostatic dipole.
Equation 5.18 for the azimuthal magnetic field
shows a l/r and l/r 2 dependence. Close to the
curren t element the 1/ r 2 term dominates and it is
in phase with the excitation current 10 • It can be
identified as the usual magnetic induction field
obtained from Ampere's law.
Equation 5.20 for the elevation axis E-field
contains terms in l/r, l/r 2 , and l/r3. The higher
order terms dominate close to the source and are
identified as the dipole and induction fields, with
the 11 r term being the radiation field which is
dominant at large distances from the source.
These equations show that the characteristics of
the field close to the source are different from
those for the field at a position far from the
radiating element. The radiation field E and H
components are in phase, spatially orthogonal
and the ratio of E to H is the free-space wave
impedance Zoo
The region in which the higher order terms
dominate is known as the near field and that
where the l/r terms dominate is called the far
field. Examination of eqns. 5.18 to 5.20 will show
that the l/r 2 terms are of the same magnitude as
the l/r terms at a distance of A/2n and this is
sometimes referred to as the near-field/far-field
boundary. A more comprehensive analysis of
near-field transition to the far field is given by
Yaghjian [19] and he classifies the boundary
distances as shown in Figure 5.7.
SIn
B
5.18
5.19
) casB
==
CWIl
1 Zo).smB
-+-.-+r
Jwcr 3 r
10 h
2
4n
where
Er
E()
H¢
r
10
h
==
==
==
Zo ==
c ==
J1 ==
f3 ==
w ==
5.20
radial electric field
elevation electric field
azimuthal magnetic field
distance from current element
current on element
length of element
impedance of surrounding medium
permittivity of surrounding medium
permeability of surrounding medium
propagation constant of medium
angular frequency of current 10
To help clarify equations 5.18, 5.19 and 5.20 note
the following relationships
w == 2 nf
5.21
wherefis the frequency in hertz
f3 == 2nlA
5.22
==
A ==
c ==
5.23
Af
where
c
c
wavelength
speed of electromagnetic wave
propagation
1/ Vii8
5.24
Zo
5.25
f3
5.26
Balanis [4] states that the reactive near-field
region is defined as that region of field immediately
surrounding the antenna where the reactive field
dominates, and is taken to exist out to a distance of
3
R
< 0.62 [ ~ ]
5.27
He defines the radiating near-field (Fresnel) region
as that region between the reactive near field and
the radiating far field wherein radiation fields
predominate and where the angular field distribution is depend en t on the distance from the
antenna. 'The inner boundary is taken to be that
in eqn 5.27 and the outer boundary is at
R
==
2D 2
T
5.28
78
A HANDB'OOK FOR EMC TESTING AND MEASUREMENT
" ,\
REGIONS OF STABLE ANGULAR PATTERN
AT FAR FIELD DISTANCES
RADIATING \
NEAR
\
FIELD
~
_1---...... REACTIVE
I
NEAH
I
FIELD
I
..
FAR FIELD
F (<1>,0) e ikr
o
r
co
"0
FIELD
DISTRIBUTION
\
IFRESNEL!
I
I
I
I :
I I
I I
I
I
~
o (O.6211"537T)
Figure 5.7
FRAUNHOFER
w
I
~
:
I
a:
w
:
o
I
2 0 2 /A
VARIATION OF PATTERN
WITH DISTANCE IN THE
FAR FIELD AROUND THE
ANTENNA PATTERN
FIRST NULL
z -10
a:
~
~ -20
>
RANGE r
~w
a:
Classification offield regions around
antennas
for D » A. The far-field region can be defined as
that region of the field of an antenna where the
angular
field
dis tribu tion
is
essentially
independent of distance from the antenna.
Outside the far-field boundary defined by eqn.
5.28 the angular distribution is not entirely
independen t of range, but the differences are
significant only at angles corresponding to the
first null in the pattern. See Figure 5.8 for the
patterns at different distances from a paraboloid
antenna [4].
Knowledge of the near-field/far-field boundary
for antennas used in EMC measurement is very
important. Most radiated measurements at box or
sub system level are made close to the equipment
under test (EDT). Often the antenna being used
either to receive or transmit with respect to the
EDT is not clearly in the far field.
In such a situation the transmitted or incident
wave cannot be accurately defined by reference to
calibrated far field behaviour. The antenna
becomes arbitrary as discussed in Section 5.2.1
and the measured signal is only meaningful in the
context of that particular situation, so that no
absolute measurements of E or H for the wave
can be made.
Figure 5.9 shows a graph taken from BS800
(now
EN550 14)
of the
near-field/far-field
boundary distance in metres against frequency
based on the simple A/2n rule. For those predominantly military tests which call for radiated
emission and susceptibility measurements to be
made at 1 ill from the EDT it can be seen that
this is only valid down to a frequency of 50 MHz.
In the case of standards for measuring
commercial electronic equipment, such as FCC
part 15 or EN55022 where radiated emission
measurements are allowable on an open site at a
-30
-40 ~_ _....a.-_""""'_-""'o...&-_--a.........
o
Figure 5.8
1t
21t
U =( DOd sine
31t
___
41t
Variation of antenna pattern with far-jield
distance. Calculated radiation patterns of
paraboloid antenna for different distances
from antenna. Source: HOLLIS) ].S.)
LYON) T.]. and CLAYTON) 1. (eds):
,Microwave antenna measurements).
Scientific-Atlanta) Inc.) July 1970
Reproduced by permission of Scientific-Atlanta
N
I
~
>()
zw
::> 100
a
w
a:::
u..
10
018TANCE FROM ANTENNA (m)
Figure 5.9
Relationship of near-fieldlfar-Jield boundary
with frequency d == A/2n
INTRODUCTION TO ANTENNAS
range of 3, 10 or 30m from the EUT, it can be
seen that the measurement is in the far field for
frequencies down to 15 MHz, which is below the
lowest frequency to be measured in the test
(30MHz).
The simple A/2rc formula yields values for the
far-field distance of only a few centimetres at
frequencies above 1 GHz. It may seem that all
microwave measurement can automatically be
carried out in the far field with a test distance of
only 1 m. In practice, this is not the case
because the antennas used in the microwave
regIme are usually of a large aperture, possibly
employing
parabolic
reflectors.
For such
antennas
the
near-field/far-field
boundary
should be defined by
distance
5.29
Usually the additional A is left out of the
calculation, but is included here to cover the
situation where the maximum aperture dimension
D in Figure 5.7 is less than a wavelength. The
Rayleigh distance to the far field should properly
be measured from the outer boundary of the
reactive fields around the antenna [19].
Using the eqn. 5.28, for the example of a 50 cmdiameter dish antenna operating at 10 GHz, the
far field is at 17m from the dish and so all usual
EMC measurements at this frequency would be
very much in the near field giving rise to results
which at the least would be difficult to interpret
and may be suspect.
5.3.9 Beamwidth
The angular width of the main beam between the
halfpower points is termed the halfpower or
-3 dB beamwidth and is a measure of the degree
to which the antenna can confine and concentrate
the radiation towards a single point. The
beamwidth may be specified in the plane of the
electric field or the magnetic field produced by
the antenna and the values are not necessarily the
same. Simplistically, knowledge of the beam
width and a separation distance from the antenna
to a point of interest will allow the spot size which
can be illuminated by the antenna to be
calculated. By reciprocity, this is also the size of
the area on an extended EUT from which
emission signals will be received most efficiently
by such an antenna.
Consider for example, an antenna aperture
which has a constant illumination function as in
Figure 5.10, producing by Fourier transform the
far-field radiation pattern shown above it. If the
illumination function is a true 'boxcar', where
from
d>
otherwise I
the form
79
to d < D/2,
I == constant
the radiated power plot will take
- D/2
== 0
5.30
The beamwid th is shown in Figure 5.10 as being
measured from the halfpower (-3 dB) points. If
one calculates the total power radiated in the
main beam between the first zeros or nulls and
divide this by the mean radiated power level
calculated over all angles the figure obtained is
called the directivity of the antenna.
Beamwidths can be calculated for real antennas
with more physically meaningful current distributions but the mathematics are nontrivial. In
Figure 5.11 a one can see the polar diagram for
dipoles of various lengths. These are calculated
[4] using the current distributions in Figure 5.11 b
and the 3 dB beamwidths are given in Table 5.3.
Note that the difference between a halfwave and
electrically short dipole is small.
Table 5.3 Calculated beamwidths for varzous dipole
lengths
Dipole length
l
«
A
l
A/4
l
A/2
3A/4
A
l
l
Beamwidth
3 dB
3 dB
3 dB
3 dB
3 dB
beamwidth
beamwidth
beamwidth
beamwidth
beamwidth
==
==
==
==
==
90°
87°
78°
64°
47.8°
Although it is possible to calculate the beam
patterns and hence beamwidth for an antenna
structure, this is usually only carried out for
specific communications antennas. Even in these
cases the patterns are always measured in an RF
anechoic chamber or on an open test range for
confirmation. Antennas for use in EMC testing
are measured individually and calibration curves
of antenna factor and a beamwidth figure are
usually supplied by the manufacturer.
Specific data are available for the 3 dB
beamwidth of certain common types of antenna
which may be used in EMC radiated emission
and susceptibility testing. For example, for
reasonably high-gain pyramidal horns the RSGB
[20] gives a graph of gain (for a 50% efficiency
horn) against 3 dB beamwidth as in Figure 5.12.
A polar diagram is given for a typical high-gain
~ntenna [21] in Figure 5.13a and a graph of 3
and 10 dB beamwidths as a function of antenna
gain in Figure 5.13b. The approximate formula
which may be used as a rule of thumb relating
gain to beamwidth is [21]
80
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
RADIATED POWER dB
Po
I
---j----OdB
5.37
3dB
Other useful approximate formulas for horns [23]
in general use are
Z
0:
~
0..
UJ
en
z
o
0..
-UJ---
en
IiI~
f)E
60
BIA (deg)
5.38
f)H
68
AlA (deg)
5.39
PEAK SIDE LOBE
- LEVEL
2 nd
NULL
+7t
PATTERN ANGLE RADS-
1 sf
NULL
and gain
I
WAVELENGTHATWHICH
ANTENNA IS OPERATING
C
Figure 5.10
.
I
Relationship between antenna physical
aperture: illumination function and
radiated far-jield pattern
3 dB beamwidth ==
I
T
27 00012
5.31
1
where G is the numerical gain (not expressed in
dB) and beamwidth is in degrees. This is identical
to
3 dB beamwidth
I
164.3jG2 (deg)
5.32
or
I
3 dB beamwidth == 2.86jG2 (rad)
5.33
Horns are one of the general antenna types used
extensively
in
EMC testing and useful
approxima te expressions for the gain and
beamwid th are [22]:
G == 10 ABjA 2
5.34
where G is the gain, A is the wavelength, and A
and B are the H- and E-plane aperture
dimensions as in Figure 5.14. Note that the
theoretical gain [20] of a long tapering horn
where a plane wave emerges at the front aperture
IS
G == 4nABjA 2
5.35
The 3 dB beamwidths in the E- and H-planes are
f)
_
E -
42,000
f)E X f)H
5.40
APERTURE IN '" s ---
"'-l
~---D-
G
51A
B
5.36
where G is the gain not expressed In dB, and f) E
and f) H are in degrees.
The exact formulas for the gain and beamwidth
of an tennas in the far field depend on the detailed
current distributions on the conducting surfaces of
the particular antenna. Thus the shape of a horn
or other antenna (length, aperture size, E and H
plane dimensions) will- affect the radiation
pattern. This accounts for the small differences
between some of the approximate formulas
presented, each of which is appropriate for that
particular type of antenna. Such formulas if used
carefully can indicate the gain and beamwidth for
other antennas, bu tare limited to those with
significant gain at the wavelength of interest [21].
Thus the EMC engineer is caught in something
of trap: a clear idea of the far-field distance and
spot size for the antennas to be used is needed but
usually the time and resources cannot be devoted
to calculating these antenna parameters from first
principles. T'he simple formulas for high-gain
antennas are all slightly different; care must be
taken not to use these for antennas for which they
were not derived. There appears to be no clear
guidance available as to the limits of applicability
of some of the rules of thumb.
In reality, the best approach for the EMC
engineer who
wishes
to
understand
the
performance and limitations of the wide range of
antennas that may be used, is to make careful
measurements, either on an open range or in an
anechoic chamber, of the antenna patterns and
gain at various distances of interest. This is not a
simple nor a quick task, however, and requires
special test equipment, facilities and time to make
reliable measurements at the range of frequencies
covered by each antenna.
The correct understanding and use of antennas
is one of the most difficult aspects of EMC
testing. As such testing becomes more important
with increasing business and legal implications
the technical uncertainties which surround the
INTRODUCTION TO ANTENNAS
00
30
ELEVATION ANGLE
e
81
100
80
0
60
40
(J)
Q)
Q)
en
Q)
"0
20
I
15
......
0
900
;-----t---+-~I---_t_-_+_-~~___tI
270 0
30
~
:2:
L5
co
co
"0
C")
10
8
6
5
4
3
2
1
15
1800
20
25
30
GAIN OF HORN ( dB )
(a)
Figure 5.12
Beamwidth against gain for pyramidal horn
Reproduced by permission of' Prentice Hall Computer Publishing
/
\
DIPOLE ELEMENTS
I_
£/2
"I-
/12----1
(b)
Figure 5.11
Dipole antenna patterns and current
excitations (a) Dipole pattern responses for
various lengths (b) Current excitation
patterns for various dipole lengths
Reproduced by permission of' Wiley
halfwave dipole beamwidth is 78° which yields a
spot size of 1.6 m at a distance of 1 m. Estimates
for other dipoles can also be made using Figure
5.11a. However for a low-gain, dipole-like
antenna operating below about 50 MHz and
working at 1 m from the EUT, calculating even a
crude spot size in this way is undesirable as
1 m < A/2n: the E UT is in the near field of the
antenna.
For a large-aperture dish reflector an tenna
working at microwave frequencies, the near field
may extend well beyond the antenna-to-EUT
distance as 1 m < 2D IA and again (assuming a
measurement at 1 m) the EUT is in the near field
of the antenna. In this case the crude spot size
may be taken to be the dish diameter D, with the
power density falling off at a rate of
24xlD (dB)
use of antennas for radiated emiSSion and
susceptibility measurements will attract greater
interest.
5.3.10 Spot size
Using the calculated or measured far-field 3 dB
beamwidth and with an antenna to EUT distance
of 1 m (as required by MIL STD 461 for
example) it is possible to estimate a rough spot
size which is approximately equally illuminated
by the antenna. Eqn. 5.33 is useful in this resp~ct
but should only be applied to high-gain antennas.
For low-gain devices such as a dipole it is possible
to use some calculated results to indicate the
beamwidth and spot size. Using Figure 5.11a the
and
4PIA
where P d is the power density at a distance x from
the edge of the beam cylinder, Pmax is the maximum power density in the cylinder, P is the
input power to the antenna in watts, A is the area
of the reflector of diameter D, and x is the
distance normal to the beam with x == 0 at the
beam edge [24]. See Figure 5.15.
Using the criterion of D« A/2 use far-field
distance of A~2n, and if D > A/2 use far-field
distance of 2D 1A.
Taking into account these comments, the farfield boundary distances have been estimated for
typical EMC antennas [25] and are shown in
Figure 5.16. The calculated spot sizes (covered by
82
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
:r:
I-
0
100
zw
8
w
6
~
4
....J
>
«
~l---1
0
2
~
lrl
B
u..
Cf)
t @]T
=KJ CD -l
I
~A---1
L = axial length to apex
A = width of aperture in H plane
8 = width of aperture in E plane
c::
W
IZ
10
..i
8
0
6
a::i'
<i
u..
0
4
c::
z
0
Ci5
2
Z
W
~
C5
(a)
15 16 17 18 19 20 21 22 23 24 25 26 27 28 29
HORN GAIN dB
30
Figure 5.14
20
Gain ofpyramidal horn in terms of its
dimensions measured in wavelengths
Reproduced by permission of Prentice Hall Computer Publishing
10
8
CI>
Q)
~
C)
Q)
applicable in the far field. The spot sizes given in
Figure 5.1 7 are shown as a broken line over the
frequencies for which the EDT is in the near field
(Figure 5.16) at 1 m and it is unsafe to rely on farfield formulas such as eqn. 5.33 to derive the spot
SIze.
6
4
"0
I
J-
0
2
~
~
«
w
co
1
0.8
gain
0.6
0.4
~
5.3.11 Effective length
27,000
(83dS)2
e 10 dB ~ 1.83
8 3dB
0.2
10
20
30
40
50
60
ANTENNA GAIN dB
(b)
Figure 5.13
Relationship between beamwidth and gain
for typical high-gain antennas (a) Typical
polar diagram of high-gain antenna
( b) Approximate relationship between
antenna gain and beamwidth
Reproduced by permission of RSGB
the 3 dB beamwidth) using the information given in
this section for typical EMC antennas [25 J are
given in Figure 5.17. The concept of a definable
beamwidth, and therefore spot size, is only really
Connor [26J defines the effective length of an
an tenna in terms of the non uniform current distribution on its surface. Such a distribution is shown
in Figure 5.11 b for a dipole. The relationship
between the effective length Le and the physical\
length L is
Le
area under nonuniform current distribution
L
area under uniform peak distribution
The effective length of a long wire antenna for
example will be a fraction of its physical length
owing to the nonuniform current induced by the
wave along its length. The shorter effective length
leads to a lower output voltage for a given
incident field strength than would be predicted
simply using the physical length of the antenna.
5.3.12 Polarisation
Balanis [4 J defines the polarisa tion of an antenna
INTRODUCTION TO ANTENNAS
f------------
ANTENNA FAR FIELD
---------IS AT 2 0 2 / A
Spot size is less than EUT size
/
Pd
T
EUT
83
Figure 5.15 EUT in
near field of high-gain
antenna D == reflector
diameter A == reflector
area
!
o
1
EUT is not in the far field
Reprod uced by permission or ArLech
House Inc.
Power density falls as 24 x / 0 dB for x > 0/2
in a given direction as 'the polarisation of the
radiated wave when the antenna is excited'. The
polarisation of the wave is defined as that
property of the radiated electromagnetic wave
describing the time-varying direction and relative
magni tude of the electric field vector; specifically,
the figure traced as a function of time by the
extremity of the E-field vector at a fixed location
in space, and the sense in which it is traced, as
observed along the direction of the propagation.
Thus the wave shown in Figure 5.4 is said to be
vertically polarised. Polarisation may be classified
as linear, circular, or elliptical. Linear and circular
polarisations are special cases of elliptical. The
sense of circular and elliptical polarisation can be
right hand (clockwise) or left hand (anticlockwise) .
In EMC testing many of the antennas such as
dipoles, biconics, log periodics and horns are
linearly polarised and require measurements to be
made in two orthogonal planes, usually vertical
and horizon tal. Antennas such as conical log
spirals are circularly polarised and
measurement needs to be made.
5.3.13 Bandwidth
Bandwidth may be considered as the range of
frequencies either side of some central frequency
where characteristics such as polar pattern, gain
input impedance, sidelobe levels, 3 dB beamwidth
or polarisation are within an acceptable value of
those at the centre frequency.
The bandwidth of an antennna is therefore not
defined by a single absolute figure. In the case of
antennas used by EMC engineers the bandwidth is
usually limited by variation in input impedance
which is specified in terms of VSWR (voltage
standing wave ratio) with respect to 50 ohms.
Engineers should be aware that all the other characteristics of an antenna (such as beamwidth, spot
size and far-field boundary) may also change with
frequency, and while the VSWR may be the
Figure 5.16 l~r-field
distances for selection of
typical EMC test
antennas
i i
5.0 - - - - - - - -...- - - - - - - - - - - - - - - - - - -....
18" dia. PARABOLIC REFLECTOR
AND FEED HORNS
4-12GHz
o.....I
W
IT:
6m@4GHz
7 m ® 12 GHz
0:
«WZ
LARGE HORN ANTENNA
400 MHz - 1 GHz
ZO
zi=
-::>
W«
00
~~
~~
Zl-
W«
2W
WO:
0:1-
::>(J)
«
W
2
only one
E
W
~
«
3.0
I(J)
o
o.....I
W
IT: 2.0
SMALL RIDGED GUIDE HORN
2-18GHz
0:
Lt.
W
o
«
20
1.0
USUAL
TEST
DISTANCE
1m
Cf).....I
I-W
ZU::
Wo:
2«
WLL
o ...
~
§§~
Cf)
«
W
2
100 MHz
1 GHz
FREQUENCY
Reprod uced by
Dynamics Ltd.
permission
or
BAe
84
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
2.5 ...- - - - - - - - -.....- - - - - - - - - -.....- - - - - - - - - -....
Figure 5.17 Estimate oj
spot sizes Jor typical
antennas used in EMC
measure- ments at
distances oj 1 m
2.0
en
~
- - - . dashed line indico1es that
EUT a1 1 m would be in the near field
and no reliable spot size can be
detennined
BICONIC
- - - - - - . - ANTENNA
1.5
Q)
E
w
N
lOOPffi~~~~~~~~~:'"
Ci5
b
1.0
0W
LAROE HORN
\
\\
SMALL HORNS \
0.5
PARABOLIC REFLECTOR "
& HORN FEEDS \
\
~
--_ ..
tt._._
TYPICAL STANDARD
GAIN HORNS
_-~
\
" ,' "
,
\
Reproduced by permission
Dynamics Ltd.
or RAe
100 MHz
100Hz
10Hz
1000Hz
FREQUENCY
obvious and limiting parameter the effect of these
other changes on the measurement should not be
ignored.
lie between 50 and 300 ohms with a dipole at first
resonance having a value of72 ohms.
5.4 References
5.3.14 Input impedance
The electrical complex impedance presented by
the antenna at its input terminals will contain a
component known as the radiation resistance
which is related to the power loss radiated away
from the antenna. I t is a fictitious resistance [26J
which represents the radiative power loss in the
antenna equivalent circuit. The radiation
resistance should be large compared with any real
resistance in the antenna (e.g. element resistance)
such that at resonance the efficiency of the device
is high and most of the power is lost to the
radiation resistance.
The antenna feed-point impedance is
2
3
4
5
6
7
8
5.41
9
where ZA is the antenna input impedance, R A is
the antenna resistance, X A IS the an tenna
reactance, and
10
R A == R r + R L
5.42
where R r is the radiation resistance and R L is the
resistive loss of antenna components. An antenna is
usually operated at or around resonant frequencies
where the input impedance is nearly resistive and
has a value which is convenient for coupling to an
external load. Typical useful antenna impedances
11
12
13
KING, R.W.P.: 'Theory of linear antennas'
(Harvard University Press, 1956)
SCHELKUNOFF, S.A. and
FRIIS, H.T.:
'Antennas theory & practice' (Wiley, 1952)
JOHNSON, R.C. and jASIK, H.: 'Antenna
engineering handbook' (McGraw-Hill, NY, 1961)
BALANIS, C.A.: 'Antenna theory analysis &
design' (Wiley, NY, 1982)
'Radio communications handbook (RSGB, 1982,
5th edn.) Chaps. 12 and 13
IEEE Transactions on Antennas
'Reference data for radio engineers' (Howard W.
Sams, 1977) Chaps. 27
D-dot sensor, model HSD-2 & HSD-4. EG & G
Electromagnetics, 2450 Alamo Avenue, SE, PO
Box 9100, Albuquerque, NM 87199, USA
MARVIN, A.C.: 'Practical notes on antennas for
EMC engineers'. Study note 2/10/79, British
Aerospace Dynamics EMC Group, Filton, Bristol, UK
BENUMOF, R.: 'The receiving antenna', Am. ].
Phys. 1984,52(6), pp. 535-538
SARGENT, j.: 'Choosing EMC antennas'.
Interference Technology Engineer's Master, 1989,
pp. 182-304
BENNETT, W.S.: 'Properly applied antenna
factors'. IEEE Trans. EMC-28 (1), 1986
BENNETT, W.S.: 'Antenna to ground plane
mutual coupling measurements on open field sites'.
Proceedings of IEEE symposium on EMC) 1988,
pp. 277-283
INTRODUCTION T'O ANTENNAS
14" KENDALL, C.: '30m-site attenuation improvement
by increasing the transmit antenna height'.
Proceedings of IEEE symposium on EMC) 1985,
pp. 346-350
15. BRENCR, C.E.: 'Antenna differences and their
influence on radiated emission measurements'.
Proceedings of IEEE symposium on EMC) 1990,
pp. 440-443
16 MISHRA, S.R. and KASHYAP, S.: 'Effect of
ground plane and charnber walls on antenna input
impedance'. Proceedings of IEEE symposium on
EMC) 1988,pp. 395-399
17 MISHRA,
S.R.,
KASHYAP,
S.
and
BALABERDA, R.: 'Input impedance of antennas
inside enclosures'. Proceedings of IEEE symposium
on EMC) 1985, pp. 534-538
18 McCONNELL, R.A.: 'An impedance network
model for open field range site attenuation'.
19
20
21
22
23
24
25
26
85
of IEEE
on E'MC') 1990,
pp.
YACHJIAN, A.D.: 'An overview of near-field
antenna measurements', IEEE Trans. AP-34
EVANS, D.S. and JESSOP, C.R.:
manual' (RSCB, 3rd edn.) p. 8.69
EVANS, D.S. and JESSOP, C.R.:
manual' (RSCB, 3rd edn.) p. 8.46
'Reference data for radio
W.
Sams, 1977) pp. 27-37
Microwave Journal tJu.,,-,~~vU,'_~\._Hh.J
KEISER, B.:
of
compatibility' (ArtechHouse, 1987)
335
EMC facility brochure BT
British
Dynamics, Filton, Bristol, UK, 1982, p. 8.7 and
1990 issue
CONNOR, F.R.: 'Antennas'
Arnold,
London) p. 2
Chapter 6
Antennas for radiated emission testing
An tennas for radiation emission measurement are
treated separately from antennas for radiated
susceptibility testing to show the importance of
different antenna parameters in the two cases.
With antennas for emission measurements the key
parameters are bandwidth, sensitivity, dynamic
range and absence of cross or intermodulation
products in the case of active antennas with built
in amplifiers. Important parameters for antennas
used in susceptibility measurements include
bandwidth, gain/power requirement, beamwidth/
spot size, power dissipation, size and mass. Such
topics are discussed in the following chapter. This
one looks in detail at the types of receiving
antennas that are widely used for radiated
emission testing. They are discussed in sequence,
beginning with the passive monopole which has
the least complicated construction.
TRANSFORMER
COUPLED OUTPUT
FROM LOADING
COIL
~50n
II
I I
: I
.1
Figure 6.2
6.1.1 Construction
These are amongst the simplest receiving antennas
used for EMC measurements. They consist of a
cond ucting rod of defined length connected to an
impedance matching circuit which usually feeds a
50 ohm cable to a matched 50 ohm input of an
EMI receiver. The impedance-matching circuit
consists essentially of a base loading coil with
sufficient inductance to resonate with the
capacitive reactance of the monopole elenlent at
frequencies of interest, see Figure 6.1. A more
sophisticated
matching
circuit
may
use
___ Monopole effective height
o
W
I
..-l
ct:
o
~
~50Q
UNBALANCED
OUTPUT
Simple impedance matching circuits for
monopole antennas
transformer coupling or a tapped loading
inductor as shown in Figure 6.2.
The design of an EMC antenna is perhaps more
complicated than that of a communications
antenna by the need to achieve good sensitivity
(good effective height) over a wide band of
frequencies. This requires that the total frequency
range of interest (usually 10 kHz to 30 MHz) for
an EMC monopole be segmented into bands with
a different impedance matching circuit for each
band.
MonDpole antennas are used mainly for testing
military equipment inside screened rooms where a
good antenna ground plane reference-is available.
I t is appropriate therefore to demonstrate its use
with reference to a n1ilitary standard.
MIL-STD 462 calls for the use of a monopole
and a typical passive antenna is 41 inches long
with an effective height of 0.5 m. Such a device
may have up to eight frequency bands as shown
in Table 6.1.
6.1 Passive Illonopoles
lI
UNBALANCED
OUTPUT
TAPPED
BASE LOADING
COIL
fe
~
Capacitance to "ground" Cm
E
I~
0W
..-l
o
0-
o
Z
o
~
~~ and~ate
em
Table 6.1 Typical monopole antenna frequency bands
10 kHz to 32 MHz in eight bands
Band
Band
Band
Band
Band
Band
Band
Band
at centre
frequency of F MHz
\
\
\
UNBALANCED
OUTPUT
RF GROUND PLANE
REFERENCE FOR MONOPOLE
Figure 6.1
Simple monopole antenna and base loading
coil
86
1:
2:
3:
4:
5:
6:
7:
8:
10 to 250 kHz
250 to 500 kHz
500 kHz to 1 MHz
1 to 2 MHz
2 to 4 :NIHz
4 to 8 l\t1Hz
8 to 16 MHz
16 to 3211Hz
AN1'ENNAS FOR RADIATED EMISSION rrESTING
87
6.1.2 Performance
The receiving antenna correction factors for a
typical commercially available passive 41-inch
monopole [IJ are given in Figure 6.3. An antenna
factor of between 24 and 50 dB must be added to
the output voltage to obtain the electric field
strength in V jm.
An example of the use of a passive 41-inch
monopole to measure the radiated emissions
from an EDT on a ground plane is MIL STD
462 note 3 test RE02-1, see Figure 6.4. The area
of maximum emission on the EDT is located by
probing its surfaces with close-in field probes and
then orientating the EDT so that this area is
facing the monopole. The antenna to EDT
separation is 1 m and the frequency range of the
test is from 14 kHz to 30 MHz. When connected
to a low-noise EMI measurement receiver the
antenna is sensitive enough to measure field
strengths of a few microvolts per metre at
10 MHz. The performance is sufficient to
measure signals in the range 14 kHz to 30 MHz
at below the specification limits for the RE02 test
shown in Figure 6.5.
A monopole measures the E- field of the incident
wave with a polarisation along the axis of the
monopole element. If the rod is vertical then the
antenna is most sensitive to a vertically polarised
E- field. The ground plane or electrical counter-
:b : : : ]
:b: : ;
.01
BAND 2
co
"'0
C/)
0::
o
I-
o
BAND 3
i1
Z
o
i=
o
BAND 4
W
o
o
c:t:
BANDS
Z
c:t:
SAND 6
BAND?
BAND 8
0.1
0.15
0.2
.25
.30
.35
.40
.45
.5
.6
.7
.8
.9
:E:
:~
:F :
~
.50
:
:
:
:
1.2
1.4
1.6
1.8
2.5
:
:
~
1.0
j
2.0
;
3.0
~
3.5
4.0
:;:: j
4.0
4.5
5.0
5.5
6.0
6.5
I
:
:
8
9
10
11
12
13
14
15
16
18
20
22
24
26
28
30
:E: : :
7.0
7.5
8.0
1
16
:k: : : =:3
32
FREQUENCY IN MHz
Figure 6.3
}'igure 6.4
Antenna factors for typical passive 41" rod
antenna suitable for use with MIL STD 461
Reproduced by permission or Camel Labs Corp.
I
Test set-up for measurement of radiated
emissions (10 kHz-30 MHz) u)ith
monopole antenna
MONOPOLE ANTENNA
FREQUENCY RANGE -
Z
o
~
~
Z
100
o
95
C/)
90
w
ow
U5
~
o N 85
~ ~ 80
~
~~
oc:t:
75
0:: :::i. 70
~ ~ 65
c:t:>
Zeo
c:t:-o
~ ~ 60
~
co
55
50 L - - _ - - - L_ _- - L ._ _.....L-:~_....J..__ _.L___~
10kHz
E
0::>
0::1.
100
1MHz
10
100
1GHz
CO z
o~­
0::
0::
c:t:
Z
FREQUENCY
Figure 6.5
FrequenC)J coverage and example of sensitivity
achievable with monopole antenna
0.25
: : :
:E:
2.0
Z
W
I-
Z
.05
1.0
0::
0::
ground Plane~
~
*Note decreasing sensitivity
at low frequencies
BAND 1
Counterpoise bonded to
poise for the monopole is at the base of the
element and must be large enough to adequately
termina te the electric field lines from the rod as
illustrated in Figure 6.1 such that the rod to
ground plane capacitance does not change significant!y if the ground plane is enlarged further.
1'he rod element uses the ground plane as its
voltage
reference
and
the
field
strength
measurement will be in error if too small a
ground plane is used. The size of the 41-inch
monopole antenna ground plane is specified in
MIL STD 461A and is 60 cm square. In MIL
STD 462 note 3 the monopole ground plane is
bonded to the E UT ground plane bench by a
solid copper extension of the counterpoise. See
Figure 6.4.
Monopole antenna measurements can be in
error if the rod element is too close to the
conductive screened room walls or ceiling. This
arises because too many of the electric field lines
associated
with
the
rod
capacitance
are
termina ted other than on the reference ground
88
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
receivers owing to the number of narrow resonant
bands which the antenna has to maintain its
sensitivity. The monopole element itself oilers a
relatively high reactive (capacitive) impedance at
its base over most of the operating freq uency range
below its self-resonance, which occurs at low VHF.
If an active amplifying device with a high input
were used to buffer the rod to the low
50 ohm ou tpu t, it would be possible to prod uce the
required impedance transformation wi thou t loss of
Moreover, a frequency shaping
network could be included in the circuitry to
produce a flat antenna transfer function. In
commercially available active monopole antennas
such as the Carnel Labs. Corporation model
95010-1 [2J, the first active element is a field-effect
transistor with a very high input impedance. This
particular active monopole has a specification
shown in Table 6.2.
I t has a single frequency compensated band over
three decades wide with a 0 dB flat transfer
function when extended to 50 inches and used with
top loading. rrhe addition of the top loading plate
increases the capacitance of the rod to the ground
plane and increases its
over the standard
41-inch configuration. This highly sensitive device
can detect narrowband emissions down to below
the levels shown in Figure 6.7a and broadband
down to those in Figure 6.7b.
SCREENED ROOM CEILING
SIDE WALL
,yv\'---"D.rtr"Y\f'D
--..,..,.............r--'~
MONOPOLE
COUNTERPOISE
6.6
ejfect oj j)lacing monof)ole antenna
too close to conducting surfaces in screened
room
Reprod uced by permission of ICT I ne.
in
6.6. l'his leads to a detuning of the
with a consequent
in the antenna
",---,..o"",+,£:>r1 in MIL STD 462
the rod
nlust
greater than 30 crn from
and 1 m from the
walls of the
room. Where
these distances
should be increased to the maXilTIUm available by
in a
chamber which is
lined with radio absorbent Inaterial (RAM).
the effectiveness of RAM at the
for which
are used is rather
limited and the
criteria for an unlined
room should be
~J..J.."'-,A.'cJ..J..~A.>
rprllllrprr.p.n1-
6.2.2 Disadvantages
Trp'r1"'£:>Yl,r""::>('
Power supP0J: A battery pack is required, usually
housed within the base box of the antenna which
also contains the active circuit. The ElVIe test
engineer must make
pack checks both
before and after each test to be sure that the
measurements are made with a properly
active circuit.
Front end damage: Care must be taken when
the rod or moving the antenna that
static
does not accumulate on the test
LLIJIJ.!.i'",--,"--l.
m.onopoles
active monofJole antenna
/lV/m)
amjJlifier)
Carnel Labs. 950101-1
10kHz to 40 111Hz
One
±1 dB from 10 to 25 kHz
±0.5 dB from 25 kHz to 40 MHz
50 inch top-loaded rod: 1 m
41 inch rod: 0.5 m
10 Mohm shunted by 8 pF
50 ohms
50 inch
loaded rod: 0 dB
41 inch
8 dB
on receiver bandwidth and frequency
.LJ'-/IJ''-/LI.'-lvil.L
ANTENNAS FOR RADIAl'ED EMISSION TESTING
NARROWBAND SENSITIVITY
+10
r-----..,------r----~--
50" TOP-LOADED CONFIGURATION
Receiver random noise BW = 1 kHz
~
>
~ -10
"0
-20L
10 kHz
...L_ _-==r:~~=~~!!!!!!!!!!~
100 kHz
1 MHz
10 MHz
40 MHz
FREQUENCY
(a)
BROADBAND SENSITIVITY
i
+70.-----,------r--------r-------,,...-+60
>
+50
"0
+40
~
-..I..-
10 kHz
(b)
Figure 6.7
-'-
100 kHz
1 MHz
- - - L_ _-L--1
10 MHz
40 MHz
FREQUENCY
Active monopole antenna sensitivity
engineer which can be discharged to the rod
element and therefore into the gate of the FET. It
is relatively easy to damage some active antennas
and they should not be moved or touched without
grounding the rod to the box.
Intermodulation distortion: Any active component only
has a limited range of operation where its transfer
function is linear. If large signals are present and
the device is working on a nonlinear part of its
operating curve then spurious distortion and intermod ula tion signals can be created. With the
dynamic range of EMC measurements often being
in excess of 60 dB it is possible to measure and
record small spurious signals at harmonic and intermod ula tion frequencies, if large signals are present
out of band. An active antenna with a bandwidth of
40 MHz is also prone to overload and signal
distortion when measuring impulsive broadband
noise. This will result in observing an incorrect
spectrum of the pulsed wavefield being measured.
Typical maximum field strengths that must not be
exceeded for the 1 m and 0.5 m effective height
monopoles [2J are given in Table 6.3.
89
connecting a balanced feeder to the elements
across the gap. A dipole can be of any length with
respect to the wavelength of an incident wave,
from a hundredth of a wavelength to a few
wavelengths. Practical dipoles for communications purposes are built to resonate with the
wavefield to maximise receiving sensitivity at a
fixed frequency. The most common dipole is a
half-wavelength long, making each element a
quarter-wave long.
For EMC measurements, dipoles must be able
to receive signals over a very wide band of
frequencies from about 30 MHz to 1 GHz. If a
single dipole is used which is for example 4 m
long, tuned to 38 MHz, t:he frequency response is
of the form shown in Figure 6.8. Thus the dipole
will only respond well to certain harmonic
frequencies in the band of interest and is not very
useful for broadband EMC measurements.
This problem can be overcome by tuning the
dipole to a new resonant length at each frequency
of interest in the band being measured. The
antenna characteristics such as correction factor
and beamwidth at the first resonance can be
established and a useful measurement of the
wavefield can be made. This is the basis of the
tuned-dipole radiated emISSIon test methods
which are required by commercial specifications
such as FCC part 15j and EN55022/BS6527/
VDE0871. However, tests carried out in this way
are time consuming and the method is not well
suited
to
automated
scanning
emission
measurement with swept frequency EMI receivers
or spectrum analysers.
A. DIPOLE
2"
I
FREQUENCY MHz
200
400
600
co
"C
W
...J
«
Table 6.3 Overload jield levels jor active monopole
()
CJ)
-20
>-
0:
Maximum
signal input
(overload)
One-metre rod: 0 dB ACF
Narrowband: 107 dBIlV/m
Broadband: 73 dBIlV/m/MHz
41 inch rod: 8 dB A.C.F.
Narrowband: 115 dBIlV/m
Broadband: 81 dBIlV/m/MHz
«0:
I-
00
0:
«
-40
w
CJ)
z
0
a..
CJ)
w
w
0:
-60
0
6.3 Tuned dipoles
6.3.1 Introduction
A dipole antenna is constructed from two long thin
co-linear conducting elements with a small gap in
the middle. The electrical ou tpu t is luade by
:::>
I-
:.J
a..
:2
«
-80
rzgure 6.8
Typical response oj tuned dipole (4 m long
at ),/2). Dipole parameters: length
400.0 cm; diameter 1.0 em; load 100
n
90
A HANDBOOK FOR EMC TESTING AND MEASUREMENT-
6.3.2 Practical tuned dipoles
Table 6.4 Tuned dipole parameters
A practical tunable dipole is shown in Figure 6.9
with telescopic elements which can be extended to
be a quarter-wavelength long over the frequencies
of interest. At resonance the dipole presents a
balanced impedance of 72 ohms across the feed
point. This must' usually be transformed by the
balun (balanced to unbalanced transformer) to a
50 ohm output for connection to a 50 ohm coaxial
cable and thence to the matched input of the
EMI meter.
The effective length of an infinitesimally thin
halfwave tuned dipole in free space is given by
Ma and Kanda [3J as
Leff == Lire
6.1
To achieve self-resonance of the dipole (zero
reactance) experience shows that it is necessary to
make it slightly shorter than a half-wavelength.
Schelkunoff [4 J derived the required length in
terms of the length-to-diameter ratio of the elements
L/D ratio
L/A at resonance
Dipole R in
50
500
50000
0.47
0.48
0.49
61
66
70
n
L
D
dipole elelnent length
dipole element diameter
dipole feed point impedance
wavelength at resonance
R in
A
The theoretical antenna factor for a thin
resonant dipole with a lossless balun and cable
connected to a 50 ohm receiver is given by Ma
and Kanda [3J as shown in Figure 6.10, where
is the dipole impedance (taken to be 70 ohms).
<a
40 ~---~---T"""-----r-----r----""
al
30
"'C
1 - 0.2257 ]
6.2
L r = (L/2) [ In(L/D) - 1
where D is the diameter of the dipole element, L is
tuned length, and L r is required length. The
effective length of a dipole near to resonance is
given in Reference 3 as
Lejjff
.
L tan(reL r I2L)
== - - - - - -
a:
0
t- 20
~
(0.025) (F in MHz)
U
«
LL
«
z
z
10
W
t-
Z
0
«
-10
50
20
6.3
re
Figure 6.10
If the dipole is shortened slightly to the required
length for resonance (eqn. 6.2), the theoretical
resistance R at resonance depends on the length-todiameter ratio. Typical values are given in Table 6.4.
100
2000r------------------..,
L / A. = 0.8
L / D RATIO = 2000
R
50n INPUT
BALUN LOSSES
\
H
T
\ ~~~f~s
~
I
1
Figure 6.9
70n 1000
CJ)
o
:><:
[8J
w
()
z
.
EMI
METER
«
~
w
a::
\
II
~
:2
BALUN
c<1-q-
EXTENSION
ARM
\
:r:
L!::====~~========:
'::::1
Z=72Q
1000
Reproduced by permission of NBS
2"
50n COAXIAL CABLE
500
Theoretical antenna Jactor Jor thin resonant
dipole
FIRST
RESONANCE
A. DIPOLE
TELESCOPIC ELEMENTS
200
FREQUENCY MHz
-1000
SWR "LOSSES"
OUTPUT CONNECTOR
V out
ANTENNA FACTOR =
--L/A. = 1.0
-2000---------------
E
Vout
Tuned and rrlatched halfwave dipole oj
variable length Jor EMC measurements
DIPOLE COMPLEX IMPEDANCE Z
Figure 6.11
c
R+j X
Complex impedance oj thin dipole as
Junction oj element length/wave length
Reproduced hy permission of
BS
ANTENNAS FOR RADIATED EMISSION TESTING
The plot in Figure 6.11 shows the complex
impedance as a function of dipole length to
wavelength with the first useful resonance close to
0.5 and the second close to 1.5.
~t--I--~--I
I
I
~
O
25
Z
20
~
o
Model OM -105 A - T1
....----20 - 200 MHz
o
«
~w
0
-5
I
l
l
SHIELDED
CASE
I
:
J __
j
,---_
I
'\
"
"'"
'J " l l
,_)(_)i-t(
I
I
I
_I
___ ~
_
I
I
I
I
I
J
BALUN
RFOUTPUT
(aj
A
r--"4A----1-4--j
\
TELESCOPING ROD
FARFIELD ANTENNA
CORRECTION FACTOR
antenna 3m. above ground
."
(\\
\\~
~p(\o
~\~Y;. 0 \0 ~e ~t\1-
r---~
s \u(\e \0 '21
.
I
I
Q\~\~s oo~(\
t5
15
~ 10
~ 5
r------ I
I
._---J
I ( ----..,/
I
I I
() tj ()
I I\:..>..)_'*l_"
TELESCOPING ROD
"'-BALUN
~
~ 35
a: 30
I
I
I
I
\
I
I
6.3.3 Commercial EMC tuned dipoles
Consider the performance of some commercially
available tuned dipoles for EMC testing to meet
civil and military standards. The Carnel Labs.
Corporation models DM~105A (T1, T2 and T3)
are a set of three dipoles [4] which can be tuned
from 20 MHz to 1 GHz. They are supplied with a
frequency calibrated 'tape measure' which can be
used to set the element lengths q uickly and
correctly without calculation. The antenna factor
for the far-field performance is shown in Figure
6.12. The solid line A is the antenna factor for the
dipole tuned to each individual frequency. It is
untuned below 27 MHz which is the frequency at
which the telescopic elements are fully extended.
At frequencies below 27 MHz the efficiency of the
dipole starts to fall as its effective length decreases,
it also becomes mismatched with the inclusion of
capacitive reactance, see Figure 6.11.
91
\e(\9J'
oo~(\
\u(\e~() ~t\1-~ ,~~
- trCC
'o~
t-
"\Oc\O
Model OM - 105 A ! T2
~\~"Y;. ':\0(\(\0
~e~\cO~ S ~
;(,."(\f?P
\
~
FREQUENCY IN MHz
Antenna factors of tuned dipoles for use
with FCC Pt. 15j (tuned down to
30 MHz) and EN55022 (tuned down to
80 MHz)
For FCC part 15j testing of information
technology equipment the dipole can be tuned
down to the lower test frequency of 30 MHz.
When testing to the European close equivalents of
EN55022/BS6527/VDE0871/CISPR22 the dipole
is tuned at all frequencies down to 80 MHz, but is
then fixed at the resonant length for that
frequency while testing is continued down to
30 MHz. In such a case the antenna correction
factor for the dipole would be that shown by the
broken line in Figure 6.12. The lower solid line B
is the theoretical antenna factor derived from the
NBS calculations in Figure 6.10. The increased
I
----I
RFOUTPUT
140 - 400 MHz
~ -102'-!-O-......3....
0 - - S 0 - - - 1......
0 0 - - -I-O----5......0.....
0--10--'00
20
Figure 6.12
I
I
I
L __
Model OM -105 A - T3
400 - 1000 MHz
~
r--'I
I
(b)
Figure 6.13
Examples of baluns (a) Wound balunfor
use at H F/ VHF (b) Stub balun for use at
UHF
Reproduced by permission of' Camel Labs. Corp.
losses in the commercial antenna over the
theoretical one are due mainly to balun losses.
A typical balun configuration used for the lower
frequencies up to 200 MHz is shown in Figure
6.13a. Similar choke designs can be found in
Reference 5. A suitable VHF /DHF balun for
tuned dipoles is shown in Figure 6.13b and
further details are given in Reference 6.
6.3.4 Radiated emission testing
Testing to meet EMC standards for commercial
eq uipmen t accounts for the major use of tuned
dipoles, but they are sometimes used to determine
'antenna induced voltage' called up by military
standards. The civil tests are commonly carried
92
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
~-------MAJOR
DIAMETER;:::
/"
~~
/ ",/
2d
------~I
--------1-- ---I~~'
MINOR DIAMETER
""-
;:::~
/
/
...........
~
\
\
/
\
\
II
DIPOLE OR - OTHER ANTENNA
'"
"'~
Figure 6.14
/
I
...........
\
-------------..;...-
~///
Plan view of open-field test site. Boundary
oj area defined by ellipse. Area to be jree oj
reflecting objects e.g. buildings)fences)
trees) poles) etc.
Reproduc~d by permission of BSI
ou t on an open-si te tes t range wi th the tuned dipole
antenna at a distance d from the EDT. Depending
on the specification and the equipment class this
distance can be 3, 10 or 30 m. The site must have
no reflecting objects within an ellipse with a major
diameter of 2d, see Figure 6.14. There must also be
a conductive ground plane of a specified minimum
size to provide unvarying ground interaction
properties. The dipoles and EUT may be set up as
in Figure 6.15.
There are anum ber of potential disadvan tages
which the EMC engineer must be aware of when
conducting radiated emission testing with tuned
dipoles. The tests can take a long time, as the
dipole has to be adjusted at each frequency of
in terest in the emission spectrum of the E UT.
Some specifications call for testing 'with both
horizon tal and vertical polarisation, and the
height of the antenna must be changed at each
frequency of interest to determine the maximum
emission level from the EDT.
For the FCC tests at low frequencies the manipulation of the large dipoles becomes a problem and
the lower element (vertical polarisa tion) gets very
close to the ground. This problem is not so severe
for the EN55022 test \vhere the dipole length is
restricted to that for resonance at 80 MHz
(elements about 1 m long).
The most serious problems arise as to what the
rather large antenna actually measures. There are
considerable mutual impedance problems due to
ground reflections [7-9] and the extended nature of
the FCC type antenna integrates the field variations
along its length: this leads to a field strength estimate
that differs from those made with the EN and
CISPR (80 MHz) antenna or a compact broadband
biconic (where permitted) [10].
Experienced test engineers are a ware of some of
these measurement problems and are careful not
to become over confident about the validity of a
technique simply as a result of its being specified
in a national standard.
Tuned dipoles are easily sensitive enough to
make EMC emission measurements when used
with a low-noise EMI receiver and quasipeak
detector. Signa~ .levels set for radiated interference
limits in standards such as EN55022 are not
difficult to achieve. These are
30 dBflV/m (QP) from 30-230 MHz
37 dBfl\T/ m (QP) from 230-1000 MHz
Ambient radio noise experienced when making
measurements on an open test range can be a
problem and this can mask the signal from the
EDT. There is little that can be done to minimise
such a problem other than siting the test area in a
low radio noise location.
6.4 Electrically short dipoles
6.4.1 Special short calibration dipoles
---1/:;;;;;
~METAL GROUND PLANE
EUT HEIGHT
TYPICALLY 1m.
ANTENNA HEIGHT
VARIES BETWEEN 1 ·4m.
Calibration dipoles are not widely used for EMC
testing but a knowledge of their existence and
some idea of how they work is essential for the
professional EMC engineer. There are two types
of calibration antennas which measure electric
and magnetic fields. They are based on short
dipoles and small loops. This section deals only
with these special dipoles used for standard
E-field measurement and calibration.
EQUIPMENT SITED ON A
REFLECTION-FREE OPEN AREA TEST SITE
Figure 6.15
Use oj tuned dipoles to measure emissions
Jrom computer equipment carried out on
open-area test site
6.4.2 Roberts dipoles
Wilmar Roberts was assistant chief of the FCC
laboratory (1967) when he undertook the
ANTENNAS FOR RADIATED EMISSION TESTING
z
::::>
-I
«
co
4
COMMERCIAL ANTENNA
3
/
'"
CJ)
2
CJ)
0
-I
ROBERTS
ANTENNA
/
co
,..,
0
20
30
50
100
200
300
500
1000
500
1000
FREQUENCY (MHz)
5
4
a::
~
CJ)
>
3
2 ROBERTS
ANTENNA
1
20
30
50
100
200
300
FREQUENCY (MHz)
Figure 6.16
VSWR and losses Jor typical commercial
balun in tunable dipole Jor EMC
measurements and Roberts balun Jor
calibration dipole
development of standard dipoles which have
an tenna factors close to those for a theoretical
tuned dipole [11]. Their chief characteristics are a
low VS WR and low balun losses over a wide range
of frequencies [12, 13]. The balun loss and VSWR
performance of the Roberts dipole are shown in
Figure 6.16 compared with commercially available
tuned dipoles such as in Section 6.3.3.
6.4.3 Small nonresonant dipoles
Electrically short dipoles can be used for some EMC
radiated emission testing. BS 727 in paraH3. 3
permits the use of a dipole shorter than half a
wavelength but longer than a tenth of a wavelength
to be used for testing commercial electronic
equipment. Short-dipole antenna correction factors
(50 ohm load) are provided in graphical form in
Figure 7 of Appendix H in that document.
Workers at NBS
(National Bureau of
Standards) in the USA produced a number of
designs for calibration dipoles [14J and spherical
dipoles have been used at the National Physical
Laboratory (NPL) in the UK. It is not intended
to deal in depth with this topic here, save to say
that the approach is based on two characteristics
of di pole behaviour.
The first is to reduce the dipole length to a few
centimetres or less [15 J which has anum ber of
effects. The device averages the field over only a
small region. The short dipole is almost purely
capacitive and presents a high reactive impedance
and is not capable of delivering the currents one
93
would expect froin a resonant dipole into a
standard 50 ohm load. I ts effective height is small
and the device is insensitive compared with a
resonant dipole.
The second is to connect a high impedance
balanced DC voltmeter across the short dipole
which has a low turn-on-voltage Schottky diode
connected across the feed point. The balanced
connection to the display meter is made using a
resistive filter line constructed from carbon
impregnated plastic in a nylon jacket. Each line
has a resistance of about 6000hm/cm. Thus a
short dipole with a practical sensitivity is achieved
by using the high-impedance detector/meter and
the wavefield is not disturbed in the vicinity of
the dipole by the balanced connections due to its
high resistance.
Although a short dipole is capable of making an
accurate field measurement almost at a single
poin t in the wavefield it has two draw backs for
use other than for controlled calibration type
testing. I t is insensitive and requires a field
strength of a few hundreds of m V /m for
operation. I t is also frequency insensitive (all
spectral information being lost in the diode
conversion to DC). I t cannot be used where more
than one signal is present at a time.
6.4.4 Microscopic dipole probes
Berger, Kumara and Matloubi describe a special
high field strength probe manufactured by
Electromechanics Co [16J which is based on the
NBS small tapered resistive dipole work by Kanda
[1 7J. The device uses diode detection and highly
resistive leads but makes use of resistive dipole
elements. It can operate fronl 1 MHz to 10GHz
within 1 dB accuracy at field strengths from 1 V 1m
to 1 kV 1m. The dipole elements, detector and
resistive leads can be seen in Figure 6.1 7.
""
TAPERED RESISTIVE
DIPOLE ELEMENTS
DIODE RECTI FI ER
...........
BALANCED HIGH IMPEDANCE
CARBON FILAMENTS
CONDUCT DC FROM THE
DIODE TO A MILLIVOLTMETER
Figure 6.17
Advanced lnicroscopic resistively tapered
dipole with built-in diode detector. The
microscopic dipole probe sensor shown next
to a sewing needle Jor comparison oj size
94
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
z
6.5 Biconic dipoles
FIELDS PRODUCED
AT POINTP
E, H (r, 8,$)
6.5.1 Introduction
CONICAL ELEMENTSOF APEX ANGLE <X
The biconic dipole is a broadband derivative of
the long thin resonant dipole. Balanis [18J gives
the theoretical basis of operation of a biconic
dipole in detail. The treatment considers
conical di pole elemen ts of infini te length and
calculates the radiation pattern and feed-point
impedance as a function of cone angle. See
Figure 6.18.
Schelkunoff [19J devised a transmISSIon line
equivalent method of calculating the feed-point
impedance for finite length small angle biconic
elemen ts. The resistance and reactance of the
feed-point impedance calculated by Jasik [20J are
plotted in Figure 6.19 and show how the antenna
becomes more broadband as the cone halfangle
Increases.
Approximations to true biconic antennas can be
made in the form of triangular sheet 'bow tie', or
bow-tie wire simulations as in Figure 6.20. A wire
bicone with approximately eight intersecting
wires has a performance almost equivalent to a
solid sheet bicone. The intersecting wire bicone is
the one most often used in EMC testing as it is
light, rugged and compact with elements about
1 m long covering the frequency range from 20 to
200 MHz.
P
.......
.......
.......
.......
.......
.......
'.I
x
Basis for theoretical calculation of radiation
fields and feed-point impedance jor
infinitely long bicone elements
Figure 6.18
6.5.2 Commercial biconic antennas
Typical commercial biconic antennas used in
EM C testing are the Emco 3108 [21 J and the
Carnel Labs. Corporation 94455-1 [22]. These
antennas consist of a pair of open stiff wire frame
bicone elements and a balun as in Figure 6.21.
For an example of the gain and antenna factor of
a commercial biconic antenna see the figures for
...--....----.----.--... 10,000
Figure 6.19 Calculated
feed-point impedance
ofjinite length bicone
relating angle to
broadband response
THIN DIPOLE
CONE ANGLES
I
'I
I,
~'\
I,
en
n'\
I \
I
I
If
~
J:
o
1,000
.5
a:
w
\
•\
;\\,\
SEE Fig. 6.18
:E
J:
o
'."-, II"f\\ ~
W
,
I
0
'\
U." \I.~\,
~
\ II II ~~
~
~
Ci5
w
a:
.....
a..
\
100
::>
I
~
o
Reproduced by permission of'McGravv-Hill
en
II \
I. I \
~\'
()
a/2= 5°
----. a 12 = 11°
- - a /2 =1/100°
1 7£:' A.
2
6
8
1st BICONE RESONANCE
10
0
1
~
2
4
1t
II A.
.
I
I
.....
,~
~
8 StCONE LENGTH
IN WAVELENGTHS
SOURCE: JASIK
ANTENNAS FOR RADIATED EMISSION TESTING
95
Table 6.5 Gain and antenna jactor for wire bicone
antenna
BOW-TIE
Figure 6.20
Frequency
Gain
Antenna factor*
(MHz)
30
40
50
60
70
80
90
100
120
140
160
180
200
220
240
260
280
300
0.05
0.07
0.15
0.50
0.59
1.06
1.06
1.05
0.50
0.93
1.19
1.34
1.33
1.16
0.90
0.97
1.17
1.00
(dB)
12.8
13.5
12.5
8.8
9.5
8.1
9.07
10.0
14.8
13.5
13.6
14.1
15.0
16.4
18.3
18.7
18.5
19.8
WIRE APPROXIMATION
Antenna shapes derived from basic solid
bicone
*Specification compliance testing -factor (1.0 m spacing)
to be added to receiver meter reading in dbpV to
convert to field in tensi ty in dBp V Im (Emco 3108)
Figure 6.21
ANTENNA FACTOR OF WIRE BICONIC ANTENNA
COMPARED WITH TUNED DIPOLES
Typical wire bicone antenna used in EMC
testing. Biconical antenna Emco 3108
§00~
EMC03108
BICONE
15
~ t;
dJLE
T2 DIPOLE
/
10
5
0
I-
~
DIPOLE - - CARNEL LABS
TUNED DIPOLES
-5 L . - - _ . L - _ - - ' -_ _- - - I
20
30
50
_ _____l
~I
100
200
400
FREQUENCY IN MHz
Figure 6.22
Antenna factor of wire biconic antenna
compared with tuned dipoles
20
z
o
i=cn
f:d"O
a::z
~~
() 0
«I-
";/,..
.......
10
z~
W
«
,,;
\
,,;
---_...
--- ........,,
............
....
,,;
....., . ./ /
zu..
IZ
...
1m ANTENNA FACTOR,,;";
,,;
15
FAR FIELD ANTENNA FACTOR
5
O~---L_--'-_---'-_--A-._......I-_.....L.-_...L-_~---'
20
6.5.3 Use of biconic antennas
Some biconic antennas are designed specifically to
drawings given in MIL-STD 461A and are used
extensively for test methods specified in MILSTD 462 from 20 or 30 MHz up to 200 or
300 MHz depending on the capability of specific
......
25
i=
&3 ~ 20
Reproduced by permission of Emco
the Emco 3108 given in Table 6.5. Note that the
antenna factor is for 1 m spacing between
calibration antennas so that it may be used for
normal military standard emission testing, and is
not necessarily the far field antenna factor, which
should be used for 10 and 30 m testing in
commercial standards. In Figure 6.22 the '1 m
close-in' antenna factor for the biconic is plotted
with the '3 m close-in' antenna factor for the T1
and T2 tuned dipoles. The shorter element length
of the biconic results in a less efficient antenna
below 80 MHz. The far field and 1 m antenna
factors for the Carnel Labs. Corporation 94455-1
are given in Figure 6.23. When the antenna is
used at 1 m from the EDT it appears to be predominantly a few dB less sensitive than for reception
of far-field signals.
30 r---r------,---~---.,----
z
o
40
60
80
100
120
140
160
180
200
FREQUENCY IN MHz
}'igure 6.23
Far-Jield and 1 m antenna factors for
typical wire biconic antenna used in EMC
testing. Biconic antenna: G'Iarnel Labs.
94455-1
Reproduced by permission of Carne! Labs Corp.
96
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
bicone models. They can also be used for some
tests specified by civil standards for commercial
electronic
equipment such
as
information
technology. For example, EN55022 (Section 10.2)
permi ts the use of aerials other than tuned dipoles
providing that the results can be correlated with a
balanced tuned dipole with an acceptable degree
of accuracy. More explicit req uiremen ts for the
use of complex broadband aerials is given in
BS727 (para H4.2).
Biconic antennas can be used with a low-noise
50 ohm EMI meter to make sensitive measurements over frequencies from 20 to 300 MHz to
detect signals below the severe levels set in MIL
STD 461 C (using a peak detector function) as
shown in Figure 6.5.
The chief advantage of a broadband biconic
antenna is that it provides good sensitivity over a
wide band and is easy to use, unlike tunable
dipoles, and enables tests to be made quickly with
automated scanning receivers or spectrum
analysers.
6.6 Wideband antennas
6.6.1 Introduction
Before the 1950s antennas with broadband input
impedances and pattern characteristics covered
frequency ratios of about 2: 1. The advanced
designs which came later extended bandwidths to
40: 1 or more [23]. These designs were referred to as
frequency independent and they had the property
that their geometries were specified by angles.
Antenna characteristics such as impedance,
beam pattern, polarisation etc. remain unchanged
when the physical size of the antenna changes,
provided that the operating frequency also
changes by the same ratio. Thus the antenna characteristics are invariant if the electrical size of the
antennna does not change. If the shape of an
an tenna is therefore completely specified by
angles then its performance is independen t of
frequency [24].
An infinite biconic dipole is one such antenna
which is only specified by the cone angle as in
Figure 6.18.
To make practical truncated
structures it is necessary that the current on the
structure decreases with increasing distance from
the feed point. If the current beyond a certain
distance is negligible the structure may be
truncated and removed. Such an antenna has a
low-end cut-off frequency above which the
an tenna characteristics are the same as those for
the infinite structure. The upper cut-off frequency
is determined by the size of the feed point which
must be less than A/8, where A is the upper cut-off
wavelength.
Although the biconic antenna or transmISSIon
line is defined by an angle, its current distribution
does not fall away to zero with distance and it
cannot be successfully truncated to form a
frequency independent antenna. Other antenna
shapes which are specified by angles do have
current distributions which decay with distance
and can exhibit frequency independent properties.
6.6.2 Log-periodic antenna
If an antenna is designed so that its physical
structure is periodic with the logarithm of
frequency, and the variation of structure is small
or negligible over a single period, then a practical
freq uency
independen t
an tenna
can
be
constructed [25]. For a more detailed explanation
see Balanis [23]. There are many interesting and
bizarre shapes which fulfil these requirements and
a variety of useful communications antennas have
been built from planar and wire log-periodic
structures, planar and wire trapezoidal toothed
log periodics and log-periodic slots. The configurations most widely used for performing EMC tests
are log-periodic dipole arrays and the conical log
spiral. Usually the first is linearly polarised and
the second is always circularly polarised.
6.7 Log-periodic dipole antenna
Consider a set of dipoles with characteristics and
spacings which change in a log-periodic manner
as in Figure 6.24. Define
6.4
and
lJ.
==
tan
-1
In
-
6.5
Xn
Ideally, the dipole gap sizes and the element
diameters should also change in a sinlilar fashion.
However, if they do not, and constant values are
used, it has little impact on the practical
performance of the antenna. If the elements are
closely spaced and all fed in phase from the narrow
end then an endfire beam propagates backwards in
the direction of the larger elements. If each
successive dipole is fed in antiphase as in Figure
6.24b the endfire beam emerges forwards from the
short end of the array. In either case, the antenna
must have a balanced feed which is usually
impractical. An unbalanced coaxial feed cable may
be used by staggering the elements and connecting
the coaxial inner conductor as shown in Figure
6.24c. This is the configuration that is most
familiar to EMC test engineers as a number of
commercially available antennas are of this form.
ANTENNAS FOR RADIATED EMISSION TESTING
97
1.0
0.9
0.8
>-
()
zw
<3
u::
0.7
I
1
0.6
u..
w ll R 0.5
L
C)
z
(a)
~
«
0::
0.4
Ci
BALANCED FEED
ELEMENTS OF
t
PHASE ...
0.3
T = 0.89
a =45°
0.2
t
0.1
O_:::;;;;;"a.._...s..-
Beam' produced
at this end
o
(b)
0.1
0.2
.&--
0.3 0.4
0.5
_
0.6 0.7
0.8
0.9 1.0
L/A
Figure 6.25
Radiating efficiency of log-periodic dipole
array. L
width oj array) a
half angle
oj apex
+8 ......- - - - - - - - - - - - - - -...
+7
COAXIAL
LINE
INPUT
+6
+5
+4
+3
+2
Figure 6.24
-....-.
50
UNBALANCED
FEED
Beam formed
at this end
GAIN
(
_....-.
_
.....
100 300 500 700 900 1100 1300 1500
FREQUENCY MHz
c)
Log-periodic dipole array antenna
(a) Array dimensions (b) Balanced
antiphase Jeed (c ) Unbalanced coaxial
feed
~~=--....:;;;a
a:
~
(J)
>
700 800 1100 1300 1500
50
FREQUENCY MHz
Reproduced by permission of Wiley
170 ......- - - - - - - - - - - - - -........
(J)
The radiating efficiency of a log-periodic dipole
array is given in Figure 6.25 showing how this
changes with the largest dipole dimension [26].
The antenna achieves 85 010 efficiency with the
largest dipole element of 0.6 A. Therefore these
antennas may be compact, at least not significantly larger than a halfwave dipole at the lowest
freq uency of interest.
Typical gain, beamwidth and VSWR (50 ohms)
for a log-periodic dipole array operating from
50 MHz to 1 GHz are given by [27] and shown in
Figure 6.26. A drawing of a typical antenna
which can be used for both EMC radiated
emission and susceptibility measurements is given
in Figure 6.27 and its performance is illustrated in
Table 6.6. The gain, VSWR (50 ohm) and
antenna factor as a function of frequency from
150 MHz to 1.1 G Hz for this typical antenna are
given in Figure 6.28.
This type of sensitive wideband antenna is ideal
@
Cl
150
130
J:
b
110
~
90
80
70
60
~
«w
CO
CO
"0
(I)
50
40 ......-50~...............1...
00-3..00-500
.......-7...
00-800
.......-11...00-1...
30-0-...150D
BEAMWIDTH
Figure 6.26
FREQUENCY MHz
Typical performance parameters Jor logperiodic antenna
for EMC measurement as scanning receivers can be
used to make rapid measurements which satisfy a
wide range of military and civil standards. I t is well
capable of measuring field strengths (in its
operating band) below the severe limits specified for
the MIL STD 461C RE02 test given in Figure 6.5.
98
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
co
"0
8.0
7.0
25
6.0
~O
~
0::
o
t-
15
40"
TYPICAL ANTENNA FACTOR
C/)
10
==:
a:
~
C/)
>
z
t-
o
LO
«
z
W
:r:
o
U
it
2.5
5
Z
«
2.0
1.5
1.0
.-..-
.-..
_ .....
a 100 200 300 400 500 600 700 800 900 1000 1100
FREQUENCY MHz
Figure 6.28
Gain, antennaJactor and VSWRJor typical
commercial log-periodic antenna.
Reproduced by permission or Amplfier Research
6.8 Conical log.-spiral antenna
Figure 6.27
o
0
o
0
0
0
0
0
0
0 00000
o
0
o
0
0
0
0
0
0
0 00000
Dimensions oj typical log-periodic antenna
used in EMC measurements (150 MJ-Iz1GHz)
Reproduced by permission or Amplifier Research
Table 6.6 Performance qf commercial log periodic
Frequency range
Power input (maximum)
150-250 MHz
250--500 MHz
500-1000 MHz
Power gain (over isotropic)
Gain flatness
Impedance
VSWR
maxlmull1
average
Beamwidth (average)
E plane
H plane
Front to back ratio
(minimum)
Connector
Size(wxhxd)
AR model ATlOOO
150 to 1000 MHz
2000 W
1500 W
750 W
6.5 dB min
7.5 dB av
±1.0 dB
50 ohms nom
Another example of a frequency independent
antenna, the structure of which is defined by
angles, is the conical spiral, a non planar extension
of a spiral-plate geometry as shown in Figure
6.29. The length L determines the lowest
frequency which can be propagated, and at
frequencies above this the pattern and impedance
are frequency independent. 1~he ends of the
spirals are tapered in thickness to provide a better
impedance match. rrhis type of antenna is
circularly polarised.
When the conducting spiral lies on the surface of
a cone, the antenna has only a single pattern lobe
towards the apex of the cone with a maximum
along the axis. Typical conical log-spiral antennas
(Stoddart 93490-1 & 93491
used for EMC
measurements are shown in Figure 6.30 with
antenna factors in Figure 6.31.
L
1.8: 1
1.5: 1
type C female
102 x 13 x 91 cm
(40 x 5 x 36 in)
Figure 6.29
Spiral plate antenna configuration.
L determines lowest Jrequenc_y that is
radiated efficiently. Feed point is at centre
ANTENNAS FOR RADIATED EMISSION TESTING
EXAMPLES OF COMMERCIAL LOG CONICAL SPIRAL ANTENNAS
Log spiral pattern conductor
printed onto conical surface
1
4 0cm
1
COAXIAL
CONNECTOR
~36an
~I
r-13cm~
1·10GHz
200 MHz· 1 GHz
ego CARNEL LABS MODEL 9349Q.1
Figure 6.30
co
~
ex:
o~
~
5
~
~
ex:
oo
Model no. 93490-1
24
23
22
21
20
Frequency coverage:
19
18
~
16
«
Examples oj commercial log conical spiral
antennas
27
26
25
«
z
m
ego CARNEL LABS MODEL 93491-2
200 MHz - 1 GHz
17
200
300
400
500
600
700
800
900 1000
_ _-
_ _- _
FREQUENCY MHz
52
co
~
50
~
48
46
ex:
r---oy---oy----r---.,--~-
_ _-
Model no. 93491-2
~
o 44
~
42
o
40
z
~
~
38
~
36
8
34
~
30
~
z
~
Frequency coverage:
1 -100Hz
32
28·
26 _ _
1
""""_"'"
. a . . - _ . a . . - _ ~ _ . . . L . - _ . . . . . I . -
2
3
4
5
6
7
8
9
10
FREQUENCY GHz
Figure 6.31
Typical log conical spiral antenna factors
200 MHz-l GHz and 1-10 GHz
Reproduced by permission or Camel Labs Corp.
99
The antenna factors are determined by the MIll
STD 461 (para 5.2.7) which is based on SAE
ARP-958 two antenna method using short
separation distances and may not produce an
antenna factor calibration which is suitable for
far-field measurements. Often the manufacturers
recommend that the far-field distance is
calculated for these log conical spiral antennas by
uSIng
far-field distance
where D is the largest diameter of the an tenna,
or 5A whichever is less. Thus for an antenna of
diameter of 25 cm the far-field distance at
200 MHz is only a few centimetres. Sometimes
it is not made clear where this distance should
be measured froIn on the antenna. The phase
centre of the antenna (defined in Chapter 5)
should be used as the assumed source of
radia tion. I t is then logical to use this as the
point
from·
which
distances
should
be
measured.
However, the phase centre moves along the
an tenna axis as a function of freq uency and the
measured an tenna factors correspond to the
various positions of the phase centre and not to a
standard distance of 1 m. Theoretical calculations and measurements by Marvin [28J have
resulted in an expression for the distance of the
phase centre from the apex of the antenna as a
function of wavelength. This can then be used to
calcula te the correction to the gain figures
obtained by the SAE ARP-958 calibration
method. The gain figures for the standard (ARP958) and corrected calibration method which
takes accoun t of phase-centre movemen t, are
given in Table 6.7 for an Emco model 3103
conical log spiral antenna.
Measured antenna patterns are shown in
Figure 6.32 for the vertically polarised E-field at
200, 500 and 900 MHz. A typical beamwidth for
this type of antenna is 90 0 and the spot size at
1 m in midband is about 2 m. The VSWR
(50 ohms) for the model 3103 is typical of this
type of antenna and is usually less than 2: 1. See
Figure 6.33.
Like all wideband frequency independent
an tennas conical log-spiral an tennas are easy to
use and automated measurements may be made
quickly. With these circularly polarised antennas
there is no need to evaluate horizontal and
vertical polarisations separately. If the polarisation components must be measured separately a
linearly polarised log-periodic dipole antenna
could be used.
100
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
Table 6.7 Standard gain for conical log spiral antenna (measured at 1 m) and corrected gain taking into account phase
centre movement with frequency
Frequency
(MHz)
Standard measured gain
(linear)
Corrected gain
(linear)
Antenna factor based on
standard gain (dB)
100
200
300
400
500
600
700
800
900
1000
0.21
1.67
2.23
2.11
2.35
2.24
1.85
2.11
1.89
2.10
2.91
3.26
2.79
2.92
2.67
2.12
2.37
2.07
2.26
17.0
14.0
16.3
19.0
20.5
22.3
24.5
25.1
26.6
27.0
Emco Model 3103
200 MHz
6.9 Horn antennas
500 MHz
900 MHz
EMC03013
Figure 6.32
1800
Example of variation with frequency
of conical log spiral antenna polar
diagram (Emco 3103)
Reproduced by permission or EMCO
3.0
ex:
~
~ 2.0
1.0
100 200 300 400
500 600 700 800 900 1000
FREQUENCY MHz
Figure 6.33
Typical VSWR for comm.ercial conical log
spiral antenna (Emco 3103)
Reproduced by permission or EMCO
At microwave frequencies where waveguides are of
practical dimensions, it is possible to radiate
energy from the open end _of the guide used as a
crude antenna. This type of antenna is almost
never used in EM C testing owing to its low
directivity [29]. Open waveguides are however
sometimes used as feeds to illuminate parabolic
reflector antennas [30J.
A horn antenna can be considered as a tapering
extension to a waveguide which provides an
increased aperture size leading to improved
directivity. The basic theory of horn antennas can
be found in almost any standard text on antennas
including [29-33J. Various types of horn antenna
which are based on rectangular and circular
waveguides are shown in Figure 6.34. The type
most frequently used in EMC measurements is
the pyramidal horn. I t is cheap to construct and
its design is well understood.
Consider the pyramidal horn in Figure 6.35
defined by its principal dimensions as shown. The
radiation pattern of a horn is determined by the
amplitude and phase distribution of E- and Hfields across the respective aperture planes. The
difference in phase over the aperture denoted by r
in Figure 6.35 is a result of the principle of equality
of path length (Fermat'-s principle). For adequate
performance most horns have this parameter r of
less than 0.25L in the E-plane and about 0.4L in
the H-plane [34 J. Expressions for the gain and
3 dB beamwidth of pyramidal horns have been
given in Chapter 5 equations 5.34 to 5.40.
Sometimes horn an tennas are used in the near
field when making EMC measurements and work
by Ma and Kanda [35J has resulted in an
addition to the Shelkunoff gain eqn. 6.34 which
should be used in the near field:
ANTENNAS FOR RADIATED EMISSION TESTING
RECTANGULAR HORNS
OJ
101
0,
"'0
en
0::
0
z .....
-()
<t:c:(
Ou..
-1
zz
0::0
0-
:r:t;
:::>
Exponentially tapered
pyramid
Pyramidal
0
w
ex:
4
3
2
5
6
DISTANCE FROM HORN m.
Figure 6.36
Typical near-field gain reductionfactorsfor
pyramidal horn at 1 GHz (Ma and Kanda)
Reprocl ucecl by permission or NBS
horn operating at 1 GHz over an antenna to EUT
distance of 1 to 6 m.
Silver [32] gives approximate formulas for the
10 dB beamwidth of typical horns with average
flare angles of 20°
Sectoral E - plane
CIRCULAR HORNS
8E
==
Exponentially tapered
cone
Figure 6.34
88A
13 deg.
31
Various possible types of horn antenna
for
79A
B/ A <
+A deg.
2.5
for A/A < 3
6.7
6.8
The radiation pattern from a typical horn with
Reproduced by permission 01' McGraw-Hili
~
\
0°
/
,
I
I
PYRAMIDAL HORN
__- - & - - - - - - - + - 2 7 0 °
900~------",-~
r ,/
E PLANE VIEW
H PLANE VIEW
Figure 6.35
180
Figure 6.37
Reproduced by permission or McGraw-Hill
G
32AB
~x RHR E
210 0
1500
E- and H-plane views of rectangular
pyramidal horn antenna
6.6
where R H and R E are the gain reduction factors
due to the E- and H-plane flares. These factors
are calculated in Reference 35 and expressed
graphically in Figure 6.36 for the example of a
0
Exalnple of E- and H-plane beamwidths
and polar diagrams for pyramidal horn
antenna (Source: Balanis). E-plane
beamwidth > H-plane beamwidth.
11 == 12 == 6A, A == 12A, B == 6A,
a == O.5A_, b == O.25A, E-plane,
- - - H-plane
Reproduced by permission or Wiley
102
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
CD
21
"C
Z
20
~
19
2
3
4
5
I
FREQUENCY GHz
; ;~~----r---.---~
3
4
5
6
7
8
9
FREQUENCY GHz
;
I
10
:~_r----r-\I'lG-\G
""--'8l--""'O
\
8
9
10
11
12
13
14
15
16
17
18
FREQUENCY GHz
Figure 6.38
Frequency coverage for horns with standard gain
20 dB) for various waveguide sizes. Typical beamwidth
of horns is 18° with sidelobes at -13 dB. Data for commercial horns manufactured by [/lann Microwave
Reproduced by permission of Flan Microwave
Table 6.8 Example of UHF horn for EMC use
specification
Frequency range
Power input (max)
Power gain
400-1000 MHz
1000 W
10 dB min typically
increasing to 15 dB at
1000 MHz
50 ohms nom
2.5:1 max
1.5:1 av
9.1 kg (20 lb)
56.4 x 79.3 x 73.7 cm
(22.2 X 31.2 X 29.0 in)
Impedance
VSWR
Weight (max)
Size (w x h x d)
Manufactured by A.R. model no AT 4001
dirnensions of those in Figure 6.35 is gIven In
Figure 6.37 [31 J.
A wide range of waveguide horns are commercially available and typical gain against frequency
data [36J for various wave guide sizes are given in
Figure 6.38:Note that the bandwidth of the horns
(and waveguides) is rather small, at less than one
octave.
At lower frequencies horns can still be used but
are usually not fed by a long waveguide. A
coaxial cable is employed and connected to a stub
in a short section of waveguide directly attached
to the horn. The specification of a commercially
available horn [37J for use in EMC testing
operating in the frequency range 400 MHz to
1 GHz is given in Table 6.8, with typical gain and
VSWR curves in Figure 6.39.
6.10 Ridged guide horn antennas
8
;;; 2.5
:2
J:
oo
2
1.0
~ 1.5
TYPICAL UHF
HORN ANTENNA
FOR USE IN EMC TESTING
~
400 500
600
700
800
900 1000
FREQUENCY MHz
Figure 6.39
Example of gain and VSWRfor
commercially available UHF horn antenna.
A.R. model AT 4001
Reproduced by permission of Amplifier Research
A single or double ridge can be introduced into a
rectangular waveguide as shown in Figure 6.40.
Marcuvitz [38J gives tables of modified cut-off
wavelengths for propagating modes and shows
that the eq uivalent transverse network for the
dominant waveguide mode is a junction
capacitance shunted by two H-mode transmission
lines with open- and short-circuit terminations.
The effect of the central ridge is to load the
waveguide and increase its useful bandwidth by
lowering the cut-off frequency of the dominant
mode [34, 39]. A thin ridge or fin is also effective
in producing the loading of a central ridge. If
such a fin is extended from the waveguide section
into a pyramidal horn, as in Figure 6.41, the
ANTENNAS FOR RADIATED EMISSION rrESTING
103
CROSS SECTION OF WAVE GUIDE
2
T
b
L
E FIELD IN
WAVEGUIDE
SINGLE RIDGE GUIDE
Ylo
0:::
~>
1.5
DOUBLE RIDGE GUIDE
2
Yo
3
4
5
6
7
8 9 10 11 12 13 14 15 16
FREQUENCY GHz
17 18
EQUIVALENT CIRCUIT
0;0
~ypical
p--'igure 6.43
A.C
T
1
VSWR againstjrequency .for
commercial ridged guide horn antenna.
Electro-Metrics RGA-100
-1
Reproduced by permission or Electro-Metrics
Figure 6.40
Single and double ridged wave guide
laboratory with a large number of antennas of
limited bandwidths. The gain against frequency
performance of a commercial wide band ridged
guide horn [41 J is given in Figure 6.42 together
with the receiving antenna factor. A typical
VSWR plot for this antenna is given in Figure
6.43 and shows a rather uneven match to 50 ohms
at the lower frequencies.
Reproduced by permission or McGraw-Hill
qp .
/
WIDEBAND
COAXIAL FEED
~I""'.
SHORT SECTION OF
DOUBLE RIDGED
WAVEGUIDE
Figure 6.41
"""I
6.11 Reflector antennas
PYRAMIDAL HORN
CONTAINING TWO FINS
Construction oj double ridged pyramidal
wideband horn antenna
Reproduced by permission or McGraw-Hill
useful bandwidth of the antenna can be increased
many times [34, 40].
This increase in bandwid th is very useful to the
EMC engineer who wishes to cover the required
measurement spectrum with as few changes of
antenna and connections to the EMI receiver as
possible. This will save on testing time and reduce
the initial capital cost of equipping the test
15
14
en
-0
Z
:;:
0
en
-0
ANTENNA FACTOR
13
Reflector antennas operate successfully when their
aperture dimensions are many wavelengths
across. They can be constructed in a number of
different ways as shown in Figure 6.44 and explanations of their design can be found in standard
antenna texts. Of particular interest to the EMC
engineer is the parabolic reflector antenna, as it is
widely used from about four to above 18 GHz for
both radiated emission and susceptibility testing.
Geometrical optics based on ray tracing may be
used to study certain aspects of these antennas,
while a full analysis requires the use of electromagnetic field theory [42J.
A parabolic surface defined in Figure 6.45 has
the property of being able to convert a divergent
beam into a near parallel one with the minimum
of aberration. This is clearly useful for point-topoint communications where narrow beamwidths
0:::
40 0
I-
12
0
<C
11
35 <C
LL
10
z
zW
9
30 ~
I-
8
7
FEED
2
4
Figure 6.42
12
10
FREQUENCY GHz
8
14
16
18
Example oj gain and antenna Jactor jor
double ridged guide horn antenna. ElectroMetrics RGA-IOO
Reproduced by permission or Electro-Metrics
PLANE
f'igure 6.44
CORNER
CURVED (fronHed)
Geon1etry oj reflector antennas
104
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
- 3 dB BEAMWIDTH
y2
= 4
fx
o
-6
-8
-4
-2
0
2
6
4
8
OFF AXIS ANGLE (DEGREES)
Figure 6.45
Geometry ojparabolic
Figure 6.46
r~flector
are used. But in EMC testing parabolic antennas
are used to increase directivity and gain over a
wide frequency range using a simple horn feed so
that small signal levels, such as those in Figure 6.5,
can be measured with a good signal-to-noise ratio.
The apparent aperture of a parabolic reflector is
given in Reference 43 as
A
==
0.54 x S
Typical polar diagram offront-jed
parabolic r~ector antenna. Parameters:
JID == 0.82) D == 25cm)f== 20.5cm)
Jrequency == 35 GHz
Reproduced by permission of Wiley
18" diam.
parabolic reflector,
7" focal length 91892 - 1
24
23
6.9
FEED HORN
where A is the apparent aperture area and S is the
physical aperture area, and the factor 0.54 is due
to the nonuniform illumination of the reflector.
The gain of this type of an tenna is
G
==
0.54 (nDIA)2
6.10
where D is the physical aperture diameter. The
3 dB beamwidth for a parabolic reflector was
given in eqn. 5.31 and can be used to drive the
following
83dB
7
X
10 4
== - - JD
CO
0
"'0
a:
0
z
w
I-
20
:b~
II
0)
II
~
~
II
LO
U
«
z
~
.....:
0
I-
Lt
-
21
to
II
~
co
~
-
I ........
co
19
if
~
Z
«
co
"'0
f
co
18
CD
N
1
2
3
4
PJ
II
0
<:>
II
0
co
"0
110
et)
16
LO
00
"'0 C\J
co
N
II
"'0
17
15
oq-
--1 J
t- -t
CD
~
6.11
where 8 is the -3 dB beamwidth,Jis frequency in
MHz, and D the physical diameter of parabolic
in feet.
An example of a typical radiation pattern
produced by a high-gain parabolic reflector
antenna which might be used in a communication
link is given in Figure 6.46 [44]. Notice that the
-3 dB beamwidth is of the order of 10.
1'ypical of conlmercial parabolic reflector
antennas produced for EMC testing is the Carnel
Labs. Corporation 91892-1 18-inch diameter
reflector with horn feeds 91890-1 (4.4-7.3 GHz)
and 91891-2 (7.3-12 GHz). The antenna factors,
gains and beamwidths (far field) are given in
Figure 6.47. The beamwidths are much larger
than for communications antennas with values of
4 to 9°.
FEED HORN
91'890-1
91891-2
4.6-7.3GHz 7.3-12 GHz
22
~
5
6 7 8 910 12
20
FREQUENCY GHz
Figure 6.47
Antenna Jactor) gain and beamwidth Jor
lJ)pical parabolic r~ector antenna used in
EMG~ testing
Care must be taken when using these antennas
in standard EMC measurements, as the
equipment under test possibly at a distance of 1 m
is almost always in the near field, with all the
a ttendan t problems of uncertainty in wave
impedance, gain, antenna factor, beamwidth and
spot size. The manufacturers of commercial
antennas for EMC measurement do not always
specify the method used to calibrate the antenna
ANTENNAS FOR RADIATED EMISSION TESTING
and derive the antenna factor and the EMC
engineer is often left to wonder if the figures
su pplied are related to the far-field performance
or tor aIm measurement.
Until manufacturers produce full traceable
performance data with their antennas, it is safest
for the EMC test specialist to calibrate antennas
using the methods approved by the appropriate
EMC standards. In the UK, antennas can be
submitted to an independent calibration serVice
such as the National Physical Laboratory.
105
140
120
CD
'U
0::
100
0
I-
~
LL
z
0
(jj
0::
80
Factor for dB I J,JV I M
50.Q input
-
60
W
>
z
40
0
0
Factor for dB I PT
50.Q input
20
0
10
6.12 Magnetic field antennas
100
1k
100k
10k
FREQUENCY Hz
6.12.1 Introduction
Figure 6.48
Loop antennas can be used to measure the
strength of the magnetic component of the electromagnetic wavefield produced by an interference
source. The design of loops varies with the
application and frequency range. In all cases the
loops are electrostatically shielded by enclosing
the wire turns inside a tubular conducting shield
which is broken at some point around the
periphery to prevent the shield acting as a
shorting turn.
Loops are used primarily at low frequencies
from a few Hz to tens or hundreds of kHz. For
example the MIL STD 462 N3 RE01 (30 Hz30 kHz) and RE04 (20 Hz-50 kHz) tests specify
the use of a 13.3 cm-diameter loop over these
frequencies. Larger loops, but with areas of less
than 1 square metre, are used for example to
measure field strengths from 100 kHz to 30 MHz
in accordance with VDE 0877 pt2. Such measurements are called for in VDE 0871/EN550 11 in
connection with industrial, scientific and medical
(ISM) equipment.
6.12.2 Passive loops
Loop antennas generate an output voltage by
magnetic induction and the relationship of open
circuit EMF (below loop resonance) and
magnetic field strength is
e
==
flr flo
N A (j) H
6.12
where e == open-circuit output voltage
flr
rela tive permeability of core
flo
permeability of free space
N == number of turns
A == area of the loop
(j)
angular frequency
H == magnetic field strength
Taking as an example the small loop, which is well
specified in the US MIL STD 461/2, the following
characteristics apply:
Antenna eonversionfaetorsfor MIL STn
loop (13.3 em dia.)
Electrostastically shielded
Diameter: 13.3 cm
Area:
139 cm 2
Turns:
36
Wire type: 7-41 Litz.
A typical comn1ercial loop antenna of this type is
the Solar Electronics 7334-1 [45] which has a
transfer characteristic shown in Figure 6.48. Notice
that the lower curve on the graph relates EMI
meter "indicated voltage to magnetic field strength
in dB picoteslas and the upper curve relates output
voltage to E-field strength in dB fl V 1m (assuming a
free-space wave impedance). Great care should be
exercised in using a loop antenna to derive E-field
strengths as most measurements at these low
frequencies are made in the near field where the
wave in1pedance is not likely to be that of free space.
As an example of using a small loop look at the
test method of MIL STD 462 N3 REO 1. This
req uires that the loop is placed 7 cm from the face
of the EUT with the plane of the loop parallel to
«
-l
00
W
I-
0
()
140
en
130
a:
'U
:r:
120
I-
110
zw
100
<:>
0::
I00
0
-l
w
IT:
()
f=
w
90
80
70
60
50
z
<:>
«
::E
10
100
1k
10k
100k
FREQUENCY Hz
Figure 6.49
M agnetie field emission lirnits for
MIL STn RE 01 test in dB pieotesla.
Limit,for RE01
106
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
co
CL
"'0
80
0:
0
....
()
«
LL
w
60
()
z
«
0
Z
0
OO
W
C-
40
a::
~
>
z 20
0
0
LU
«
0
...J
~
son
U
«
z
z
....zLU
«
co
0
...J
0
600n
100kO
-20
0.01
0.1
1.0
10
100 250
FREQUENCY IN KILOHERTZ
}-'igure 6.51
Antenna conversion factors for large loop
76.2 cm diameter
6.12.3 Active loops
Figure 6.50
Example of typical loop antenna emission
nleasurement (MIL SYD 461j2 RE04).
Plane of loop should be 90° to plane of test
sample face
the face. The EUT is then examined to find the
position of maximum radiation at each frequency
of interest and the levels are recorded and
compared with the permissible limit which is
shown in Figure 6.49. Small loop antennas may
also be used at greater distances from the EUT.
Such a test configuration is called for MIL STD
462 N3 RE04 and is shown in Figure 6.50 with
loop positioned at 1 m from the EUT.
Larger passive loops are also used for measuring
magnetic field strengths in this way. An example is
the Carnel Labs. Corporation 94608-1 [46] which
has the following specification:
Electrostatically shielded
Frequency range: 20 Hz to 250 kHz (calibrated)
usable up to 30 MHz
Diameter:
76.2 cm (30 in)
Area:
0.456 m 2
Turns:
11
Load impedance: 50, 600 or 100 kO
The antenna conversion factor for this loop is
given in Figure 6.51. It could be used in VDE
testing but would require additional calibration
up to 30 MHz. Another example of a large
diameter loop antenna which can be used for
VDE or TEMPEST (secure communications)
testing is the Electro-Metrics ALP-70 [47] which
has a diameter of 63.5 cm (25 in) and is calibrated
from 10 kHz to 30 MHz.
To ex tend the frequency range of a loop antenna
without either incurring a large number of band
switches, or reducing the number of turns (and
the sensitivity) to avoid loop resonance, while at
the same time equalising the freq uency response
a t low freq uencies, it is necessary to develop an
active loop antenna. An active broadband
amplifier is included in the antenna in the same
way as for the active E-field monopole. Thus the
same comments apply with regard to battery
power and overload distortion (see Section
6.2.2). An example of a commercially available
calibrated active loop is the Electro-Metrics
ALR-30A [48]. Tl1is device has a diameter of
43 cm (17 in) and is calibrated from 9 kHz to
30MHz.
6.12.4 Loop calibration
There are a number of ways of calibrating loop
antennas [45, 49] but the most common approach
is the coplanar two-loop method. This is shown in
Figure 6.52 where the generating loop produces a
known field strength along the axis of the loop to
be calibrated by measuring the voltage developed
across a calibrated resistor to derive the driving
loop current. A similar calibration technique is
specified in IEEE Std 302 [50] where the loops
are situated 1 m apart.
Investigations by Millen [49] have shown that
there are wide variations by up to 7 dB in the
measurements of magnetic fields made by
different commercial loop antennas in testj
calibration situations. The greatest problems
occur near the loop resonances. He concludes that
loops do not produce the same output voltages in
uniform and nonuniform fields and that it is not
ANTENNAS FOR RADIATED EMISSION TESTING
POWER SIGNAL GENERATOR or
SIGNAL GENERATOR and AMPLIFIER
1 Q PRECISION
RESISTOR
IN SERIES
WITH LOOP
107
~ 12 em-----1
LOOP BEING CALIBRATED
(RE 01)
TRANSMITTING LOOP
( RS 01)
I
I
I
I
13.25"
33.57 em.
~
\
I
0.3 em I
LOOP (n = 10 tums) OF
00.16 INSULATED
-L . . . . - - - - - - - -
"!T
COPPER WIRE
5 em
-"-----
llo---_
--
_=___
(a)
Figure 6.53
L
J
1.0n
PRECISION
RESISTOR
(b)
Figure 6.52
Co-planar two-loop calibration setup
( a) Illustration oj'layout (b) Circuit
schematic
Reprocl ucecl by permission of Solar Electronics
valid to calibrate loop antennas in a nonuniform
field, such as that which would be produced with
two separated coplanar loops.
To achieve the most accurate measurements,
loop antennas should be calibrated in a uniform
field which could be provided by a Helmholtz
coil. Currently this would require the test
engineer to calibrate his own loops, which will
take time and involve some equipment costs.
Whether this is done or not, engineers should be
aware of these calibration problems, and should
expect an additional measurement uncertainty
due to calibration factors when making magnetic
field measurements.
6.12.5 Magnetic field susceptibility tests
A typical magnetic field susceptibility test is that
specified in MIL STD 461/2 as RSOI (30Hz30 kHz) where a small 12 em-diameter loop is
wound with ten turns of insulated copper wire as
shown in Figure 6.53. In the test the face of the
radia ting loop is placed 5 em from the face of the
EDT being investigated. The alternating voltage
across a calibrated resistor in series with the loop
is measured to derive the current in the loop to
produce the required field strengths.
~~~E~~~DUCTING
B is measured here
Loop specifiedfor magnetic field radiated
susceptibility test ( MIL S T D 461/2
RSO1). For this configuration oj loop:
B == 5 x 10- 5 T/ A at measurement face.
Loop self-resonance occurs at above 100 kHz
:5en
w
b
usa.
LIMIT FOR RS 01
~
~
~160
en
8
10-
~140
I:§ 120
1A
1
10-2
10-3
~ 100
I-
~ 80
w
60
~ 40
10-5 ~
10-£ ~
20
o
ow
o
i=
w
z
":E
c(
10
ff
:c
10-4 ::
r::
~
~
g
100
1k
10k
100k
a:
:5
aw
a:
FREQUENCY Hz
Figure 6.54
Limits of magnetic field strength Jor
MIL STD 461C pt. 4 RS 01
susceptibility test
The test limits are given in MIL STD 462 N3
directly in dB,uV across the calibrated resistor. In
later versions (MIL STD 461 C pt.4 the field
strength limits which the EDT must withstand
are given in Figure 6.54, together with the
approximate loop driving current required to
produce the field.
The use of various loop antennas in lowfrequency EMC field measurement illustrates that
generally, military EMC standards require a
wider range of tests, over a broader range of
freq uencies and using a wider range of antennas
than do standards relating to commercial
electronic equipment. I t is inevitable therefore
that tests in military EMC standards have been
used to illustrate the use of the widest range of
antennas, sensors and measurement techniques.
108
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
6.13 References
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
Passive Monopole Antenna 94592-1, Carnel Labs.
Corporation, 21434 Osborne Street, Canoga Park,
CA 91304, USA
Active Monopole Antenna 95010-1, Carnel Labs.
Corporation, 21434 Osborne Street, Canoga Park,
CA 91304, USA
MA, M.T. and KANDA, M.: 'Electromagnetic
compatibility and interference metrology'. NBS
technical note 1099, NBS,. Boulder, CO 80303,
USA, july 1986, p. 76
Carnel Labs. Corporation instruction manuals for
tuned dipoles DM-I05A-Tl/T2 & T3, Carnel
Labs. Corp., 21434 Osborne Street, Canoga Park,
CA 91304, USA
'RSGB radio communications handbook'. Potters
Bar, Herts, UK, 1982, 5th edn., p. 12.42
'RSGB radio communications handbook'. Potters
Bar, Herts, UK, 1982, 5th edn., p. 13.6
McCONNELL, R.A.: 'An impedance network
model for open field range site attenuation'.
Proceedings of IEEE symposium on EMC, 1990,
pp. 435-439
KENDALL, C.: '30 m site attenuation improvement
by increasing the transmit antenna's height'.
Proceedings of IEEE symposium on EMC, 1985,
pp. 346-350
BENNET, W.C.: 'Antenna to ground plane mutual
coupling measurements on open field sites'.
Proceedings of IEEE symposium on EMC, 1988,
pp. 277-283
BRENCH, C.E.: 'Antenna differences and their
influence on radiated emission measurements'.
Proceedings of IEEE symposium on EMC, 1990,
pp. 440-443
DASH, G.: 'A reference antenna method for
performing site attenuation tests'. Proceedings of
IEEE symposium on EMC, 1985, pp. 607-611
'A new wideband balun'. FCC project 3235-16
dated 3/4/57
'Construction and testing of antenna balun
assemblies for general purpose use by the Field
Engineering Bureau'. FCC project 3235-25, dated
10/11/67
MA, M.T. and KANDA, M.: 'Electromagnetic
compatibility and interference metrology'. NBS
technical note 1099, sections 6 & 7, NBS, Boulder,
CO 80303, USA
CAMELL, D.G., LARSEN, E.B. and ANSON,
W.J.: 'NBS calibration procedures for horizontal
dipole antennas'. Proceedings of IEEE symposium
on EMC, 1988, pp. 390-394
BERGER, H.S., KUMARA, V. and MATLOUBI,
K.: 'Considerations in the design of a broad band
E-field sensing system'. Proceedings of IEEE
symposium on EMC, 1988, pp. 383-389
KANDA, M.: 'An isotropic electric field probe with
tapered resistive dipoles for broad band use,
100kHz-18GHz'. Proceedings of IEEE symposium
on EMC, 1986
BALANIS, C.A.: 'Antenna theory, analysis &
design' (Wiley, NY, USA) chap. 8, pp. 322-330
19 SCHELKUNOFF, S.A.: 'Electromagnetic waves'
(Van Nostrand, NY, 1943) chap. 11
20 jASIK, H.: 'Antenna engineering handbook'
(McGraw-Hill, NY, 1961) chap. 3
21 Emco Biconical Antenna 3108 instruction manual.
Electro-Mechanics Company, PO Box 1546,
Austin, TX 78767, USA
22 Carnel Labs. Corporation biconic antenna 94455-1
instruction manual. Carnel Labs. Corp., 21434
Osborne Street, Canoga Park, CA 91304, USA
23 BALANIS, C.A.: 'Antenna theory, analysis and
design' (Wiley, NY, USA) chap. 10 pp. 413-435
V.H.:
'Frequency
independent
24 RUMSEY,
antennas'. IRE National Convention record,
part 1, 1957, pp. 114-118
25 'Reference data for radio engineers' (Howard W
Sams) chap. 27, p. 27-17
26 ISBELL, D.E.: 'Log periodic dipole arrays' IRE,
1960, AP-8 (3), Fig. 7
27 'Antennas, antenna masts and mounting adaptors'.
American Electronic Laboratories Inc, Lansdale,
Montgomeryville, PA 18936, USA, catalogue
7.5M-7-79
28 MARVIN, A.C.: 'Gain and phase centre evaluation
of the EMCO conical log spiral antenna'. BAe EMC
study note 005, 29/1/79, British Aerospace
Dynamics, Filton, Bristol, UK
29 COLLIN, R.E.: 'Antennas and radio wave
propagation' (McGraw-Hill) p. 182
30 RUDGE, A.W., MILNE, K., OLVER, A.D. and
KNIGHT, P. (Eds.): Handbook of antenna
design, Volume 1. (Peter Peregrinus, London,
1982) chap. 4
31 BALANIS, C.A.: 'Antenna theory, analysis and
design' (Wiley, NY, USA) chap. 12, pp. 532-571
32 SILVER, S.: 'Microwave antenna theory and
design' (Peter Peregrinus, London, 1984) section 10
33 SOUTHWORTH, G.C.: 'Principles and applications of waveguide transmission' (Van Nostrand,
1950) section 10.1
34 KRAUS,j.D.: 'Antennas' (McGraw-Hill, 2nd edn.)
p.647
35 MA, M.T. and KANDA, M.: 'Electromagnetic
compatibility and interference metrology'. NBS
technical note 1099, NBS, Boulder, CO 80303,
USA, chap. 5.3, pp. 67-72
36 'Standard gain horns' data sheet. Flann Microwave
Instruments, Dunmere Road, Bodmin, Cornwall,
UK
37 Antenna data sheet for AT 4001. Amplifier research
(USA), EMV Ltd, 11 Drakes Mews, Crownhill,
Milton Keynes, UK
38 MA.RCUVITZ,
N.:
'Waveguide
handbook'
(McGraw-Hill) section 8.6, p. 399
39 COHN, S.B.: 'Properties of the ridge waveguide'.
Proc. IRE, August 1947, 35, pp. 783-789
40 WALTON, K.L.
and SUNDBERG, V.C.:
'Broadband ridged horn design', Microwave ].,
March 1964,7, pp. 96-101
41 Operating instructions for RGA-I00. ElectroMetrics, 100 Church St, Amsterdam, NY 12010,
USA
42 CONNOR, F.R.: 'Antennas'. (Edward Arnold,
London, 1984) section 5.3, pp. 53-57
ANTENNAS FOR RADIATED EMISSION TESTING
43 'Reference data for radio engineers' (Howard W
Sams, 1977) chap. 28, p. 28-20
44 BALANIS, C.A.: 'Antenna theory, analysis and
design' (Wiley, NY, USA) chap. 13, p. 616
45 'Calibration
of loop
antennas,
RFljEMC
Instruments, components and accessories for the
RFI jEM C engineer'. Solar Electronics Co, 901
North Highland Ave., Hollywood, CA 90038,
USA
46 Carnel Labs. Corporation loop antenna 94608-1.
Carnel Labs. Corp., 21434 Osborne Street, Canoga
Park, California 91304, USA
47 Electro-Metrics loop antenna ALP-70, Electro-
109
Metrics Ltd, I vel Rd, Shefford, Beds., SG 17 5JU,
UK
48 Electro-Metrics loop antenna ALR-30A, ElectroMetrics Ltd, Ivel Rd, Shefford, Beds., SG17 5JU,
UK
49 MILLEN, E.: 'A comparison of loop antennas'.
Proceedings of IEEE symposium on EMC, 1990,
pp. 451-455
50 IEEE Std 302-1969: Standard methods for
measuring electromagnetic field strength for
freg uencies below 1000 MHz In radio wave
propagation. IEEE, 345 East 47th St, NY,
NY 10017, USA
Chapter 7
Use of antennas for radiated
susceptibility testing
7.1 Introduction
7.1.2 Standards requiring immunity tests
The types of antenna commonly used for RF
radiated
susceptibility
testing
are
treated
separately from antennas used in emISSIon
measuremen ts as the an tenna parameters relating
to reception and transmission are differen t.
Radiated susceptibility testing is carried out
regularly and extensively on military equipments
before going into service. Each country, and
sometimes each armed service in that country, has
a specification and set of test methods which will
direct the testing in a detailed way. Important
EMC
testing
standards
covering
military
equipment are listed in Chapter 2.
Many EMC standards relating to commercial
electronic equipment do not as yet require
radiated susceptibility or immunity testing to be
carried out as part of product certification.
Examples of exceptions being IEC 801-31
BS666 7-3
for
ind ustrial
process
con trol
equipment,
EN55101-3
for
information
technology equipment and NWML0320 for
certain items of metrology eq ui pmen t. There is
also a European harmonised generic immunity
standard EN50082-1 relating to any domestic,
commercial or light industrial equipment not
covered by a prod uct specific imm uni ty
standard.
Radiated susceptibility testing is one of the most
expensive aspects of EMC assessment. This is
mainly due to the capital cost of the range of high
power broadband RF amplifiers needed to drive
the variety of an tennas used to cover frequencies
up to 1 GHz (civil) and 18 or 40 GHz (military).
Free-field tests must be conducted in a metalscreened room of sufficient size to house the EDT
and test antenna as shown in Figure 7.1.
Reflections should be suppressed whenever
possible by using radio absorbent material on the
walls and ceiling inside the room as shown in
Figure 7.2. The screened room and radio
absorbent material are also costly items and
increase the capital investment which must be
made by the test laboratory if radiated susceptibility testing is to be performed.
In what follows, antennas commonly used in
free-field EMC radiated susceptibility testing are
described individually and typical field strengths
produced for various input RF powers indicated.
This is followed by a similar treatment for
bounded-wave devices.
7.1.1 Types of antennas used in
susceptibility testing
Antennas for EMC radiated susceptibility or
immunity testing. fall into two classes: free
wavefield and. bounded wavefield, addressed
separately in this chapter. Generally, free-field
antennas are used for tests on large systems or
subsystems, and on units at frequencies above
30 MHz. Bounded-wave devices such as parallel
plate lines are generally used for testing small
units about 30 cm high at frequencies below
300 MHz. There are of course exceptions to these
generalities and bounded-wave devices for
example can be used to test large vehicle systems
at kV 1m field strengths in NEMP (nuclear electromagnetic pulse) measurements. Small units or
components can be tested in bounded-wave
devices (with extended frequency coverage up to
1 GHz) such as Crawford cells or GTEM
(gigahertz transverse electromagnetic mode)
cells.
Free-field antennas are not as efficient at
producing high field strengths (over a large
volume) as bounded-wave devices are over a
small volume. In many cases of conformance
testing, the use of free-field antennas or
bounded-wave devices is specified over a given
frequency range by the EMC standard which
applies to the EDT. For those development tests
where the EMC engineer has some discretion in
choosing antennas, the more efficient boundedwave devices will probably be chosen if the size
of the EDT and test frequency range permits.
The bounded-wave radiators are less costly, and
wi th some closed devices wi th no RF leakage
such as a Crawford cell, the tests may be carried
out in an ordinary laboratory rather than a
shielded room.
110
USE OF ANTENNAS FOR RADIATED SUSCEPTIBILITY TESTING
III
where Pd is the power density in Wjm 2 and Pin is
the input power to the antenna in watts. Relating
the E-field strength to the wavefield power
density by the impedance of free space, the input
power required for various E-field strengths in
Table 7.1. is calculated from
7.4
In the case of a practical antenna with a slightly
lossy balun, such as the Carnel Labs DM-I05A
TljT2jT3 which were discussed in Chapter 6,
where the gain is given as 0 dB from 27 to
1000 MHz, eqn. 7.4 becomes
E
SIGNAL SOURCE &
POWER AMPLIFIER
2
== 30
X
Pin
7.5
Table 7.1 Input power required for various field strengths
Figure 7.1
Field
strength
at 1 m
Standard test set up in screened room for
radiated susceptibility testing
Vjm
1
10
100
1000
Reproduced by permission of BSI
ANECHOIC CHAMBER
POWER
SUPPLY
I.
TRANSMITIING ANTENNA
1
i
:_~
Figure 7.2
Radio absorbent material lining inside oj
screened room used for radiated susceptibility
testing
Reproduced by permission of BSI
FREE-FIELD ANTENNAS
7.2 Tuned halfwave dipoles
Lossless tuned halfwave dipoles
approximate effective area A given by
A
0.13A 2
GA
[IJ
have
an
A
--
so gaIn
G
0.13 x 4
G
1.63 or 2.1 dB
4n
[2J
Lossless
DM-I05A TljT3
W
W
0.02
2.04
204
20449
0.033
3.33
333
33332
Reasonable field strengths of around 10 V jm at
1 m can be obtained for a few watts input RF
power. Thus the dipole antenna is quite efficient
when used at resonance. It would be impractical
to use a dipole with some loss (such as the DM105A T IjT3 designed primarily for reception) to
generate fields above about 100 V jm as the balun
and other lossy components would begin to heat
and sustain damage.
The problem with using tuned dipoles for EMC
radiated susceptibility testing is that relatively
efficient performance with a low VSWR is
restricted to the frequencies close to the dipole
resonance. The antenna therefore has to be tuned
at each frequency of interest when testing across
the required band and this would be very time
consuming. I t is for this reason that tuned halfwave dipoles are rarely used In practical
immunity testing.
7.1
2
and also
Power input
7.2
Using eqn. 5.2 the approximate power density on
an EUT at 1 m from the lossless tuned halfwave
dipole is calculated as
7.3
7.3 Biconic dipoles
This type of broadband antenna is described in
Chapter 6. It is often used for both radiated
emission and susceptibility testing in the
frequency range 20 to 300 MHz because of its
wide bandwidth which is achieved without any
length adjustment. This makes it convenient to
use during swept frequency testing which reduces
test times and therefore keeps costs to a minimum.
112
A HANDBOOK FOR EMC TESTING- AND MEASUREMENT
Care must be taken to ensure that biconic
antennas that are suitable for radiated emission
testing are also capable of handling the RF
power for radiated susceptibility testing. Some
receiving antennas may have baluns which are
too lossy or have built-in resistive networks to
aid matching or the production of a flat
frequency response. In such cases the power
dissipated in these lossy elements could lead to
overheating and damage.
High-power biconic antennas such as the Emco
3108 (discussed in Chapter 6) are specially
developed for radiated susceptibility testing. As
an example of the performance of such an
antenna, the power requirements for given field
strengths at 1 m are shown in Table 7.2.
Table 7.2 Approximate power requirements against
frequency for field strengths at 1 m spacing
Frequency
MHz
30
40
50
60
70
80
90
100
120
140
160
180
200
220
240
260
280
300
Typical
gaIn
0.04
0.08
0.13
0.38
0.59
0.94
1.00
0.98
0.69
0.76
0.88
1.31
1.62
1.42
1.04
0.90
0.80
1.02
frequency is also given and reference is made to a
commercial log-periodic dipole antenna produced
by Amplifier Research, Model AT 1000. The
average gain (calibrated at 1 m) for this typical
antenna is 7.5 dB ± 1 dB and if a small loss is
assumed of 0.5 dB for connectors etc., it is
reasonable to use an average gain figure of 7 dB
or a factor of five.
In a similar manner to deriving eqn. 7.3, for
this log-periodic antenna the relationship
between input power and wavefield power
density at 1 m is
5Pin
7.6
0.398Pin
4n
where Pd is the power density at 1 m and in a
similar manner to eqn. 7.4 for the log-periodic
antenna:
E2
377
E2
150 Pin
X
0.398 Pin
Field strength
1 Vim 5V/m 10V/m 20V/m
W
0.83
0.42
0.26
0.088
0.056
0.035
0.033
0.034
0.048
0.044
0.038
0.025
0.021
0.023
0.032
0.037
0.042
0.033
W
21
11
6.5
2.2
1.4
0.88
0.83
0.85
1.2
1.1
0.95
0.63
0.53
0.58
0.80
0.93
1.1
0.83
W
83
42
26
8.8
5.6
3.5
3.3
3.4
4.8
4.4
3.8
2.5
2.1
2.3
3.2
3.7
4.2
3.3
W
332
168
104
35
22
14
13.2
13.6
19.2
17.6
15.2
10
8.4
9.2
12.8
14.8
16.8
13.2
I t is now possible to calculate the approximate
input power required to produce a given field
strength at 1 m from this log-periodic antenna.
Figure 7.3 shows the relationship in graphical
form for field strengths from 10 to 100 V 1m. This
low loss and robust commercial antenna for
example, can produce field strengths at 1 m of up
to 500 V 1m and handle input powers of over
1.5kW.
50---....-----r----.----~-----.
J : - 40
I-w
00::
zlWW
o::~
30
1- . . . . .
(J)(J)
01-
20
...J...J
wO
u:~ 10
0
Emco 3108 high power biconical antenna
At 200 MHz this antenna is almost as efficient as a
lossless tuned dipole, but is less so at the edges of
the band over which it operates. At 30 MHz
where it is electrically short and inefficient (being
physically only 1.3 m long) it requires 40 times as
much power for the same E-field as a lossless
tuned dipole.
7.7
0
2.0
The simplified theory of operation and typical
construction of this type of antenna is discussed in
Chapter 6. Typical gain as a function of
10.0
120
J: -
100
~~
80
I-W
~~
~ 00 60
a~
rf! ~
U-_
40
20
7.4 Log-periodic dipoles
4.0
8.0
6.0
POWER (WATTS)
30
40
POWER ( WATTS)
50
60
LOG PERIODIC ANTENNA AT 1000 (150 MHz - 1 GHz)
Figure 7.3
Power against field strength at l,m for
typical log-periodic dipole antenna
Reproduced by permission of' Amplifier Research
USE OF ANTENNAS FOR RADIATED SUSCEPTIBILITY TESTING
7.5 Conical log-spiral antennas
This type of antenna is also discussed in Chapter 6
and typical gain against frequency figures are
given. The typical midband gain for the commercially available Emco 3103 (calibrated' for 1 m) is
about a factor 2.3 or 3.6 dB. Deriving the relationship between E-field at 1 m and antenna input
power,
7.8
Typical input powers for various field strengths are
given for this conical log-spiral antenna in
Table 7.3.
Table 7.3 Power against field strength for typical logconical spiral antenna at 1 m spacing
Frequency
MHz
100
200
300
400
500
600
700
800
900
1000
Gain
Field strength
1 Vim 5V/m 10V/m 20V/m
0.13
1. 72
2.07
2.43
2.35
2.38
2.08
2.17
1.89
1.46
W
0.256
0.019
0.016
0.014
0.014
0.014
0.016
0.015
0.018
0.023
W
6.409
0.484
0.403
0.343
0.355
0.350
0.401
0.384
0.441
0.571
W
25.6
1.9
1.6
1.4
1.4
1.4
1.6
1.5
1.8
2.3
W
102.4
7.6
6.4
5.6
5.6
5.6
6.4
6.0
7.2
9.2
113
produce a truly frequency-independent value for
the constant which relates electric field strength to
antenna input power as in eqn. 7.8 for example.
However, as a guide, take a single gain value of
10 dB at a frequency of 580 MHz and use it to
derive the value of E at 1 m as
7.9
This yields an input power requirement of 83 W
for a field strength of 200 V 1m at 1 m and at a
frequency of 580 MHz. It is evident from this
simple calculation that the use of a horn antenna
of this type is an efficient way of producing high
field strengths at 1 m suitable for EMC radiated
susceptibility testing. Graphs of field strengths
which can be produced at 1 m by the AT4001
horn antenna for a number of input powers can
be seen in Figure 7.4.
For standard .gain waveguide horns such as
those referred to in Figure 6.38 the average gain
for a given waveguide size is about 20 dB ± 1 dB.
Deriving the approximate relationship between
field strength and input power as in Section 7.2,
7.10
Thus for a field strength of 10 V 1m at 1 m only
0.33 W is required. Care must be taken when.
using simple far-field gain formulas such as eqn.
5.2 on which these calculations are based, when
considering high gain antennas which may have
extended near fields out to beyond the usual
antenna to EDT distance of 1 m.
Emco 3103 conical log-spiral antenna
Although the manufacturer shows the antenna
being usable down to 100 MHz the VSWR as
shown in Figure 6.33 rises to almost 4: 1 at this
frequency. If it were used to create a significant
field strength of say 20 Vim at 1 m (requiring an
input power of around 100 W) care would be
needed to avoid reflected power causing damage
to the RF power amplifier output stage. For this
reason many modern commercial amplifiers for
use in EMC testing have output stage protection
in addition to current trips to prevent reflected
power damage.
1000
800
W
ex:
rw
600
400
~
(f)
r....J
200
0
>
::c
r-
100
80
Z
60
ex:
r(f)
40
0
W
0
....J
W
7.6 Horn antennas
The theory and design of horn antennas is discussed
in Chapter 6 and typical gain against frequency
figures are stated for pyramidal horns. An example
of a large low-frequency horn used for EMC
radiated susceptibility testing is the AR AT400 1.
1'he gain varies from 10 dB at 400 MHz to 15 dB at
1 GHz (Figure 6.39). It is therefore not possible to
u:
20
10 ~---"'_~_..I--_.L--~_~_-'
300 400 500 600 700 800 900 1000
FREQUENCY MHz
Figure 7.4
Field strength at 1 m produced as function of
frequency for various input power levels from
pyramidal horn antenna
Reproduced by permission or Amplier Research
114
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
7.7 Parabolic reflector antennas
The characteristics of the parabolic reflector
an tenna are also discussed in Chapter 6 and
typical gain and beamwidth figures are given for
commercial antennas which are widely used for
EMC measurements at microwave frequencies.
As an example, the Carnel Labs 91892-1 18-inch
diameter reflector and two horn feeds (91890-1,
4.4-7.3 GHz and 91891-2, 7.3-12 GHz) are
shown in Figure 7.5. Table 7.4 lists the antenna
gain values, gives the field strength/power
constants and indicates the approximate relationship between field strength at 1 m and required
in pu t power to the antenna feed horns at the
upper and lower freq uencies of the bands
covered.
rl_
HORN FEED
(7.3 - 12 GHz)
i -1
4cm
Figure 7.5
/~
HORN FEED
( 4.4 - 7.3 GHz )
COAXIAL INPUT
CONNECTOR
Parabolic reflector antenna andfeed horns for
use in radiated susceptibility testing
Table 7.4 Power against field strength table for an 18inch diameter parabolic reflector antenna
Frequency
4.4GHz
Gain dB
Gain (x)
£2
7C Const.
7.3 GHz
7.8 Radiated im.m.unity field
strength requirem.ents
7.8.1 Requirements for commercial
products
REFLECTOR DISH
18" diam.
antenna at, say, 7.4 GHz, it would result in a very
high field strength at 1 m from the dish of approximately 1.9 kV/m.
The near field/far field boundary for the 18-inch
(46 cm) parabolic reflector antenna at a frequency
of 7.3 GHz calculated from eqn. 5.28 is approximately 10m. An EDT at 1 m from the antenna is
clearly in the near field and care must be
exercised in applying simple formulas to derive
the field strength for a given input power to the
antenna. The experienced EMC test engineer will
where possible, calibrate his own antennas at the
various ranges of interest and derive a more
precise set of power tables which can be used with
confidence.
12GHz
23
200
28
600
32
1600
fiOOO
18000
48000
The approximate relationships derived for the
electric field strength (at 1 m) as a function of
antenna input power and the tables of typical
val ues produced from them, have been set ou t for
a number of antennas commonly used in EMC
radiated susceptibility testing: The tables are
calculated for field strengths in the range 1 to
100 V /m as this covers the values commonly used
in immunity testing to meet most civil and
military standards.
The field strength specified in the civil standard
IEC80 1-3/BS6667-3 (Susceptibility to radiated
electromagnetic energy of industrial process
measurement and control equipment) over the
frequency range 27-500 MHz is normally restricted
to 10 V /m or less. This is typical of current
standards applicable to commercially produced
electronic equipment. These levels may increase in
the future as the commercial and domestic EM
environmen t becomes more severe, as has been the
case in the military field over the last ten years.
7.8.2 Requirements for civil aircraft
Field
strength
at 1 m
Vim
1
10
100
Required input power
4.4GHz
7.3 GHz
12GHz
mW
0.16
16.6
1660
mW
0.05
5.5
555
mW
0.02
2.08
208
Octave-bandwidth travelling wave tube power
amplifiers are available which can produce up to
200 W output at these frequencies. If this power
level were applied to the parabolic reflector
Concurrent with the introduction of digital cockpit
instrumentation and fly-by-wire technology, the
proposed field strengths which civil aircraft must
withstand increased dramatically at the end of the
1980s [3]. The new draft certification requiremen ts are being proposed for aircraft to
demonstrate that they can operate safely in a
high-intensity radiated field (HIRF). This has
implications for both equipment (EMC standard
DO 160 ch.20) and system level testing. An
example of the draft RF environment (world
wide) is given in Figure 7.6 and shows worst-case
peak field strengths of over 10kV /m.
USE OF ANTENNAS FOR RADIATED SUSCEPTIBILITY TESTING
E
>
....
I
"zex:w
100,000
10,000
-"'1.-"'"1.'LII r -
1,000
L_J
....00
100
0
-'
w
10
u::
1
.01
1
.1
10
100
1,000 10,000 100,000
FREQUENCY MHz
--PEAK
------AVERAGE
Draft worldwide severe RF environJnent
(116190 )
Figure 7.6
115
limits in the HF band have been addressed [4]
and nonradiative methods of susceptibility testing
have been devised using high power Bel current
probe injection techniques [5-8] and direct
injection of RF into the structures of items for
test. The recently introduced BCI (bulk current
injection) techniques will be dealt with In
Chapter 9.
In the following section the design and use of
susceptibility antennas for use at HF and below
are discussed and the problems of generating
other than modest field strengths are explored.
7.9 E-field generators
7.8.3 Mili tary req uirements
In the military EMC world, MIL STD 461 also
shows this trend towards higher field strengths
specified for radiated susceptibility tests. Figure
7.7 gives the levels required by MIL STD 461A/B
for the RS03 test when applied to equipments
from all three services. In general the values are
below 100 V 1m bu t in special cases (some aircraft
on carrier decks) the limit is raised to 200 V 1m.
I t can be seen by extrapolating from Table 7.2
(biconic antenna) that to test even small
equipments to this level would require power
amplifiers with outputs of 1.3 kW at 100 MHz and
16.8 kW at 40 MHz. Such powerful test
equipment would be very expensive and special
ultra-Iow-Ioss antennas would be needed to
survive this power input. In general the situation
becomes worse at lower frequencies where
antennas have a lower power gain, and becomes
critical in the HF band where inefficient 'fringe
field transmission line' antennas (discussed subsequently) are commonly used.
It is at present impossible to carry out for a
reasonable cost a 200 V 1m radiated susceptibility
test through the HF band on a complete system
which has dimensions of more than a few metres.
The problems of susceptibility testing to the RS03
10 VIm (Navy & USAF)
300
/
40 Vim (Navy) -
(all services)
--L......
10
I
(all services)
pi
Jo----ool
31
HIGH LOCAL
liE" FIELD
I
\
30-
0.3
An E-field generator, as its name implies, is not
exactly an antenna. It is a compact radiating
device which produces a localised high electric
field in its vicinity. It does not have a well-defined
radiation pattern and does not produce an
intentional beam of any _kind. These devices
sometimes exploit the fringe radiation from a
short open transmission line which is energised to
a high voltage from a powerful amplifier via a
broadband RF step-up transformer.
A sketch of a transmission line antenna is given
in Figure 7.8 and shows the transmission line
200 V1m for non-metallic aircraft and
above-decklf~selage equipment
\
100~
7.9.1 Construction
_
(Army & USAF)
1 Vim (Army)
,.",
10 kHz 100 kHz
1 MHz
I
I
10 MHz 100 MHz
I
1 GHz
I
POSITIONING OF
10 GHz 100 GHz
II
IIE FIELD GENERATOR AND EUT
FREQUENCY
Figure 7.7
Radiated susceptibility limits for us services
as given in MIL STD 461 A and B
(Test RS03)
Figure 7.8
Typical construction oj high E-Jield
generator
116
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
rails, the impedance transformer/balun and the
high power low inductance loads. In some designs
the load is external to theE-field generator. The
EDT is usually placed 1 m to the side of the
device in the fringe field of the short transmission
line. The live rails, or plates, can often be
extended to the side of the main an tenna to
provide a higher field region between them.
A reasonable impedance match is made to the
power amplifier by the use of the high power low
inductance RF absorbing resistors across the rails
and VSWRs of around 2.5 to 3: 1 can be achieved
prior to the EDT being pu t in place or the
antenna being operated in a small screened room.
Generators constructed in this way are not
efficient but have a wide bandwidth, from 10 kHz
to 30 MHz, as the loading on the amplifier is
essentially resistive.
A wide-bandwidth transformer is used to step
up the RF voltage from the 50 ohm input by up
to a factor ten to increase the voltage across the
transrnission line and thereby increase the E-field
produced between the rails and around the
device. A
circuit diagram and electrical
parameters for a typical genera tor are shown in
Figure 7.9.
A. R. Model AT 3000
Figure 7.10
Reproduced by permission
~2kW
~1
3 : 1 RF TRANSFORMER
(WIDE BAND)
kV
500n
HIGH
POWER
LOAD
1
d = 1m
I
I
E FIELD
~
1 kV 1m
SHORT TRANSMISSION LINE "RAILS
Figure 7.9
Typical construction of high-jield strength
local E-field generator
Compact highfield strength/high power
local E-field generator
II
or Amplfier Research
they become self resonant. The field strength can
vary considerably with frequency for a constant
input power and it is usually impractical to
expect to produce a given field strength at a
particular point close to the generator simply by
measuring the device input power and extrapolating from a calibration curve. An example of
the variability of field strength with frequency
for a constant 1 kW input power is given for a
moqel EFG3 when used in a reflecting screened
room in Figure 7.11.
E-field generators are therefore normally used in
conjunction with a small broad band (10 kHz300 MHz) E-field monopole detector which may
150
7.9.2 Practical devices
Several commercial designs of wide band E-field
generators are available. Typical of these are the
IFI EFG3 [9J (10 kHz-220 MHz) and the
AR AT3000
[10J
(10kHz-30MHz).
The
generators
for laboratory
use
are about
1 m X 1 m X 8 cm and are mounted on a nonconductive stand or tripod. They may have
extending arms or rods which enhances the field
between them. A diagram of the AR A T3000 is
given in Figure 7.10.
Although E-field generators can operate over a
wide frequency band they do not always have a
well behaved frequency response at VHF where
E
; 100
o...J
W
u:
w
50
0.01
.1
1
10
100 200
FREQUENCY MHz
Figure 7.11
Example of variation in field strength for
constant input power of unlevelled E-jield
generator inside shielded chamber
Reprod uced by permission
or BAe Dynamics
lISE OF ANTENNAS FOR RADIATED SUSCEPT'IBILITY TESTING
HIGH POWER E FIELD GENERATOR
10 - 100 V / m constant field strength
1====;:::::====::1
SMALL BATIERY POWERED
_________E FIELD MONOPOLE SENSOR
FIBRE OPTIC LINK
~/
L== ==1
RF POWER
AMPLIFIER
100 W - 2 kW VARIABLE OUTPUT POWER
J?igure 7.12
E-field generator used to produce known
levelled E-field againstJrequency.
be coupled via a fibre optic link to a broadband
RF levelling preamplifier as in Figure 7.12. The
input power from the main amplifier is then automatically controlled to produce a constant E-field
at the position of the sensor. If the maximum
output power required from the main amplifier is
greater than that which can be supplied, the
levelling will not take place and the E-field will
fall below that demanded. The VSWR of the Efield generator varies with frequency and may
exceed the limits into which the amplifier can
drive the power. Under these circumstances the
protection devices in the amplifier will trip out
and shut off the power. This is more likely to
occur when a large EDT is being tested, or when
the E-field generator is working in a small
screened room with insufficient spacing to the
walls, floor or ceiling.
Even with the limitations described, at first sight
the levelling technique overcomes the problem of
the highly variable frequency response of the Efield generator. However, when the EDT is
placed in the field and the E- field sensor is placed
on, or close to it, this will still result in a different
levelled field. That is, the levelling now takes
place taking into account the diffraction field
from the EDT. The diffraction fields of the EDT
have thus been compensated for by the levelling
loop and the field strength to which the EDT is
subjected is not the same as that which would be
derived by using the levelling loop without the
EDT present.
To overcome this problem it is possible to use
computer-based instrumentation to record the
input power needed as a function of frequency to
produce the levelled field without the EDT
present and to replay these power settings when
the EUT is in place. This will then subject the
EDT to a known calibrated field, providing it is
117
not so large as to significantly alter the intrinsic
performance of the E-field generator
mutual
impedance coupling to the active elements. The
exact manner in which these tests are conducted
is still to some extent a matter for the EMC test
engineer.
E-field generators produce fields with different
impedances at different frequencies as the EUT is
almost always in the reactive near field of the
device. The wave impedance is usually greater
than that of free space, particularly at low
frequencies from 10 kHz to a few tens of MHz.
Thus the susceptibility of the ED'T may not be
that which it would be if subjected to a free-field
plane wave with the same field strength. Indeed,
using these generators it is often difficult to know
exactly what wavefield the EDT has been
subjected to, apart from knowing the one
parameter which is measured (E-field).
I t is possible to produce reasonably uniform
fields over a large volume by constructing devices
up to 3 m high and 2 m wide. An example of such
a large E-field generator is the AR A T300 1
(10 kHz-20 MHz) which can be used to subject
systems up to the size of small vehicles to high Efields. This commercial device has a frequency
response which is shown in Figure 7.13.
E- field ge~<;ra tors are very inefIicient devices and
require a few kW ofRF input power to generate a
few hundred V 1m fields over a relatively small test
volume of around a cubic metre. This makes the
test method extremely expensive as it requires a
broadband kW RF power amplifier. More efficient
bounded-wave devices for conducting EMC
radiated susceptibility tests on small equipments
are considered subsequently.
FIELD STRENGTH BETWEEN ELEMENTS
sao r__--.---..------,--,---r---,--Ir----.---r---r-,-----,
W
"S 400
~ .~300
~ :g 200
-- 3':
(J)o
1-0
c5 ~ 100
>"5
so 0'----.0L...
-.01--.....J......--L.1-..J..2--.S1---1L--~-~--'7":::----=-=-----=-!.50
os
2
1
FREQUENCY MHz
GENERATOR SPECIFICATION (A.R. AT 3001 )
Power input, cw maximum
3000 watts
Frequency range
10kHz· 20 MHz
Impedance
50 ohms, VSWR 2.5:1 maximum, 1.5:1 average
Electric field intensity ( at 2500 watt input)
200 vim minimum between elements
RF irlput IconnlBctor
'
'yp" v female
Figure 7.13
Field strength Jor given power as function
ojfrequency, Jor large commercially
available E-field generator (EUT size
2x3x2m)
Reproduced by permission or Amplifier Research
118
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
7.10 Long wire lines
7.10.1 Advantages
Another form of E-field generator or antenna that is
capable of producing high field strengths is the long
wire line. This technique has the advantage over
short transmission line E-field generators in that
they operate in the dominant TEM (transverse electromagnetic mode) using the conductive enclosure
in which they are erected as the outer sheath of a
coaxial line [11 J. This allows some understanding of
the field pattern and the wavefield impedance at
points around the wire and in the vicinity of the
EDT. The equipment being tested is placed under
the wire in the screened room and it should be small
compared with the size of the room (less than a
quarter of the linear dimensions of the room). Long
wire lines can therefore be used for generating high
field strengths on relatively large objects (0.5-1 m 3 )
if used in a good sized screened enclosure. Test
objects of this volume would normally be too big to
be tested in a parallel plate line or other bounded
wave device (discussed later in this chapter).
The long wire line can only be used below about
30 MHz [11 J in the average sized screened room
used for example for EMC susceptibility testing to
MIL STD 461 (5 x 4 x 3 n1), as higher order modes
will be set up at frequencies above this and the
ordered nature of the TEM field will be destroyed.
7.1 0.2 Use in testing military equipment
The MIL STD 462
example of an EMC
radiated susceptibility
shown in Figure 7.14.
notice 3 [12J is the best
standard which calls for a
test using a long wire line as
The line is suspended tautly
between two insulators mounted on the opposite
walls of the screened room, below the ceiling level,
at between 1/4 and 1/3 of the height of the room.
A coaxial feed is constructed from a 1 in. diameter
copper pipe with a 16 AWG bare wire centre
conductor. The outer of the coaxial line is
grounded to the wall of the room at its base and
the signal generator or power amplifier connection
is also made to the coaxial feeder at this point. I t is
preferable to have the signal generator or power
amplifier outside the room (for convenience and
safe operation) but the length of the connection to
the feeder should be kept as short as possible and
certainly less than one tenth of a wavelength at
30 MHz (1 m). If the amplifier or signal generator
is inside the screened enclosure and the coaxial
feeder centre conductor is extended to connect to
the amplifier output, its length must be kept to less
than 1 foot (30 cm) [11 J.
There is a careful procedure which must be
followed in MIL STD 462 N3 to derive the
values for the terminating resistors (R 2 and R 3 in
Figure 7.14) for any given long wire installation.
These resistors correctly load the feeder and long
wire line so that the generator can feed RF power
to a well matched line to radiate in the room at
frequencies up to 30 MHz. Once the noninductive
loading resistors have been determined the same
val ues maybe used each time the line is erected
to conduct a test. The final configuration is shown
in Figure 7.15 and the equation relating the Efield produced at the test sample to the driving
voltage at the base of the feeder (which is the
transmitting antenna factor, T AF) is
7.11
where E L is the driving voltage, E the E-field on
the centre line of the EDT and kd the attenuation
constant (TAF),
7.12
INSULATORS
~
R3
J
COAXIAL
FEEDER
Field strength at
EUTis EV/m
DRIVING VOLTAGE EL
Figure 7.14
Typical screened room layout for using long
wire antenna (MIL STD 461)
Figure 7.15
Geometry for long wire line relating field
strength at E UT to driving voltage
USE OF ANTENNAS FOR RADIATED SUSCEPTIBILITY TESTING
where d) d1 and d2 are the distances shown in
Figure 7.15, and Z is the characteristic impedance
of the long wire line (R 2 ) . The a tten uation
constant (TAF) is independent of frequency
resulting in the straightforward performance of
the radiated susceptibility test when using a long
wire line. Although the T AF will be a good guide
to the relationship between the E-field generated
at the EUT and the driving voltage or input
power (unlike the case of E-field genera tors) it is
advisable to have a small fibre optically coupled
E- field sensor [ 13J at the E UT location to
measure the actual E-field generated.
The long wire line maybe considered as a freefield radiating antenna, wi thin the confines of the
screened room. I t is also equally tenable to
consider it as a simple TEM bounded-wave
device with the screened room itself forming the
ou ter conductor of a coaxial line.
BOUNDED-WAVE DEVICES
Bounded-wave devices is the name given to a class
of EM-field generating devices where the radiation
is largely confined by the radiating structure. This
tends to make these devices efficient but only in
generating fields over a small volume.
7.11 Parallel-plate line
contribute to the upper frequency of simple
lines for use in an EMC laboratory, being
limited to about 30 MHz.
The larger the EUT the larger must be the line to
accommodate it, and thus the lower must be the
upper frequency limit of the line. Very large
parallel-plate lines have been built which approximately simulate predominantly low-frequency
(less than 10 MHz) nuclear electromagnetic pulse.
Complete vehicles can be irradiated in such lines
at high field strengths of around 50 kV 1m.
7.11.2 Line impedance
The characteristic impedance of a parallel plate is
the key design parameter. I t determines the voltage
across the plates for a given input power and
therefore determines (crudely) the E-field as this is
the plate voltage divided by plate separation. The
characteristic impedance itself is determined by the
physical configuration of the line:
7.13
where Z is characteristic impedance of the
parallel-plate line, L the inductance per unit
length, and C the capacitance per unit length. It
can be shown [15, 16J that for an air-filled line
the approximate impedance is
7.11.1 Properties
The parallel-plate line is the simplest of the
bounded-wave devices and a line of about 0.5 m
separation is capable of producing high field
strengths of up to a 100 V 1m for moderate input
RF powers of less than 100 W. There are two
main limitations in its use for EMC susceptibility
testing:
(i)
(ii)
The height of the EUT is restricted to about
one third of the line spacing. 'This means
that for practical laboratory lines of less
than 1 m separation [14J the EUT must
have dimensions of less than 30 cm. For the
parallel-plate line specified in MIL STD 462
(notices 1 and 3) with a plate separation of
18 inches (46cm) the EUT can have no
dimension larger than 6 inches (15 cm) if it
is to be tested in all three axes.
The useful frequency range of the susceptibility test is limited by the cut-off frequency
for the line where higher order modes begin
to propagate in addition to the simple
TEM. The overall VSWR of the line is
determined by the InJection and load
rna tching sections at either end of the
parallel section and by the variation of line
ilTIpedance with frequency. All these factors
119
Z == Zo
X
hlw
7.14
if h « w (i.e. h < O.lw), where
h == plate separation
w == plate width
Z characteristic line impedance
Zo == impedance of free space (377 ohms).
7.11.3 Construction
The construction of a simple parallel-plate
which is suitable for testing to MIL STD
RS03 is shown in Figure 7.16. I t can be seen
the line is a sizable laboratory device which
line
462
that
can
POWER INPUT
END
Figure 7.16
Parallel stripline jor radiated susceptibility
test RS03 US MIL STn 46112
120
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
SOURCE
PARALLEL PLATE LINE
LOAD
50n
SIGNAL
SOURCE
520
800
(b)
Parallel plate
line
(0)
Insertion loss
=4.2dB
7.17
46.4Q
(c)
Insertion loss
=30dB
son
test a small item of equipment with
dimensions less than 6 inches (15 cm) . The
dimensions of the line lead to a characteristic
of 83 ohms and to drive it froln a
conventional 50 ohm signal source an impedance
network is required. This -is -shown in
7.17 a and has an insertion loss of 4.2 dB.
.
line termination is shown in Figure 7.1 7c and
IS a
83 ohm load with a voltage divider
attenuator with a 50 ohm output for connection
to an EMI meter which enables the RF voltage
across the
to be measured. A suitable
attenuator in the line to the EMI Ineter has a loss
30dB.
A
calibration factor for the stripline is
shown
7.18. A field strength of 100 V jm
can be
with 25 W dissipated in the load
which
65 W from the 50 ohm signal source.
A
150 ohm impedance parallel-plate line
with a 0.8 In
separation for use in
commercial
to the DIN
45 305 [14] standard is shown in Figure 7.19
with the
and load circuits. This
line
tapered sections from the
to the source and load resistive networks to
122
n
Q: :Q61~: Z=150Q
Matching networks at input and load ends
of RS03 parallel stripline
SOURCE
SOURCE PAD
Figure 7.19
LINE
Example ofparallel-plate line usedfor
testing commercial equipment (DIN 45305)
reduce the effects of sharp impedance discontinuities which adversely affect the VSWR.
~ more sophistica ted line [1 7] is required for
testIng commercial equipment to IEe801-3j
BS6667-3 in the frequency range 27-500 MHz and
is shown in Figure 7.20. The test volume of the line
is defined by a cube of 0.8 m side. The maximum
recommended EDT size is a cube with a 25 cm
si?e. 1~he lin~ has two tapers each 0.8 m long but
stIll uses reSIstor pads for the source and load
matching networks. The condition associated with
eqn. 7.. 14 clearly does not hold (as the plate
separatlon and wid th are identical) and the characteristic impedance cannot be calculated using this
TERMINAL STRIP
WOODEN PLANK
SUPPLY t INPUT &
OUTPUT CABLES
( 3 + 2 + 2 wires)
~
All cables
are twisted
METAL BOX WITH FILTERS
TERMINAL STRIP
(see fig. 7.21 )
I
24 r---,--,---r--,---,----,--r---.---.---
~
22
~
20
18
16
~
~
QE
TERMINAL STRIP
(9 tags)
HF MEASURING
PROBE
uI 00
14
iI ~ 12
EARTH
~~ 10
t-
&1
6
W
4
..J
BLOCKS OF WOOD
(400 x 200 x 125 mm)
8
SUPPORT OF
FOAM PLASTIC
2
0o~_~--=----:~~-~--'--...1.--L--l--J
1
2
3
4
5
6
7
8
9
10
V - VOLTAGE ACROSS LOAD ( VOLTS)
7.18
calibration chart for RS03 1WIL
461 parallel stripline
Figure 7.20
FRAMEWORK OF WOODEN BEAMS
( section 50 x 50 mm )
Parallel-plate line with tapered source and
load sections IEC/ 801-3 for testing
industrial electronics
Reproduced by permission of BSI
USE OF ANTENNAS FOR RADIATED SUSCEPTIBILITY TEST'ING
simple formula. The value of the matched load is
135 ohms which is close to the line impedance.
rrhis particular line is specified for use up to
500 MHz, which is high considering the large
plate separation. I t is fed in such a way that the
live plate is the lower one which sees the ground
plate above it and the actual ground below it is
separated by 0.4 m. This is a crude coaxial configuration which can help to extend the upper
frequency of the line. The design does not include
distributed RF absorbing materials to provide RF
damping which are sometimes used in highperformance lines. Care would be needed when
carrying out tests in this line and the test engineer
should monitor the actual E-field components in
the line, preferably at points along its length, as
the test frequency is changed.
I t is interesting that this IEC80 1-3 stripline
makes provision to extract the EDT cables via a
set of filters placed above the top (grounded)
plate, and then run them down the tapered input
section to the inpu t RF connector. They are then
twisted around the RF coaxial cable for some
distance away from the line before being
connected to the EDT support equipment. This
configuration helps to minimise the interaction
between the EDT cables and the fields in the line
so that the test will predominantly reveal the
susceptibility of the box of electronics rather than
its connecting cable.
The EDT box is tested in three axes to determine
the worst-case susceptibility. Schemes have been
suggested [ 18J to reduce the testing time by
mounting the EDT at 45° to the plates in both
longitudinal and transverse axes and then rotating
it through 360° to expose all facets of the EDT to
the maximum field. Such novel approaches have
not yet been included in test standards.
7.11.4 Complex lines
I t is possible to design more sophisticated parallelplate lines using long and carefully tapered transmission lines or wave launchers of complex
geometry. A 6 m long tapered line with aIm
separation and multiple strip conductors instead
of plates (to reduce transverse currents) has been
built [19J to operate at frequencies above 30 MHz.
A large 1 m plate separation design using a wave
launcher is specified in AFSC DH 1-4 [20J as
shown in Figure 7.21. I t uses a distri bu ted load
made from conductive plastic sheets with
377 ohm/square. Because it uses no lumped
resistor matching pads it is extremely efficient and
can produce a consistently high field strength as a
function of freq uency. A field strength of 10 V /m
can be produced for just 0.83 W from DC to
20MHz. See Figure 7.22.
121
WAVE LAUNCHER DETAIL
BNC orN TYPE
CONNECTOR
~
6m~
1m
~
TERMINATION
comprising 3 separate layers of
377 n /0 conductive plastic film,
joined at ends and connected
to plates
INPUT
CONNECTOR
WAVE LAUNCHER
;'-6 copper on Perspex
11
Figure 7.21
Sophisticated parallel stripline "Loith wave
launcher US AFSG'V DH 1-4
Reproduced by permission of' US DoD
i
1000
~
100
0::
10
w
~
a.
I-
~
~
for 10 V / m
1 ...
-'
.1
W = E2 = 100 = 0.833 W
120
.01
.001 L...--_---'-_ _. . I - _ - . . . L_ _- L -_ _L - - _ - - ' - _ - - - - - I
10
100
1k
10k
100 k i M
10M 100 M
FREQUENCY Hz
AFSC DH 1 - 4 LINE
F'igure 7.22
Zc
Power inputfor 10 Vim field in efficient
parallel-plate line. No source or load
resistive pads
Reproduced by permission of' US DoD
7.11.5 Field uniformity and VSWR
All parallel-plate lines suffer a degradation in field
uniformity and VSWR when an EDT is
introduced into the line. A study made by Anke
and Busch [15] has produced an estima te of the
VSWR seen at the input of the parallel plate line
specified in MIL STD 462 when EDT objects of
various sizes are introduced into it.
Let the wid th of the line be Wand the height of
the line be H. Now let the height of the object be h
and its wid th be equal to that of the line, and
define R == W/H and r == W/(H h). Then
hili == 1 - R/r and the VSWR at the input to the
line is given in Figure 7.23. The effective value of
R for the MIL STD line is about 1.5 and the
standard req uires that 'in no case shall the test
sample be closer than 10 cm to the top plate'.
Thus the ratio of the maximum height of the
object to the height of the line (h/H) is 0.78 and
r == 6.8.
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
122
5r-----~-----,...---::I.-----,------.
a:
~ 2.5
line performance! However, a strong VSWR
effect would be noticed at about 50 MHz with
this EDT in the line where the impedance reaches
over 200 ohms compared with the ideal value of
83 ohms.
>
7. 11.6 Use in screened room
o
(R~~~5)
0.5
~---.
LIMITATION OF MIL STD 46f
Figure 7.23
VSWR at input to parallel-plate line as
Junction oj relative height oj E UT to line.
Let W == width ojplate line, H == height
ojplate line, h == height oj EUT.
Define R == WIH, r == WI (H-h) ,
hlH == l-Rlr
Tracing these values onto the R == 1.5 curve (for
the MIL STD line) the worst-case VSWR for an
EDT which is only 10 cm less than the 46 cm
pIa te height will be close to 3: 1. Anke and Busch
[15J measured the input impedance of the MIL
STD line as a function of frequency up to
100 MHz and revealed an increase above the
nominal 83 ohms which starts at 8 MHz and
peaks with a value of 154 ohms at 20 MHz. See
the heavy line trace marked 2 in Figure 7.24.
This shows that the relatively simplistic design of
the MIL STD line is rather inadequate at the
high end of its specified operating frequency
range of 30 MHz. When an EDT is placed in the
line which is 50 cm long X 50 cm wide and 30 cm
high, the measured input impedance of the line
changes to that shown as the light trace 1 in
Figure 7.24. Within the 30 MHz frequency range
the insertion of the EDT actually improves the
200..-------,-------y---r--...".-----.,
W
z
::Ja
A parallel-plate line will radiate a significant
amount of energy away from itself and must be
used inside a shielded enclosure for all but the
lowest power tests. Porter [21] has conducted
experiments to determine the effect of a screened
room on the performance of a parallel-plate line
derived from that specified for testing con1mercial
electronic equipment in IEC80 1-3, as discussed
earlier. A particular a.pplica tion of this line has
been incorporated in a report [22] and is used by
the DTI to satisfy the requirements of ECE
Reg.13 (annex 13) [23] and 85/647 EEC annex x
[24] with regard to the immunity of antilock
braking devices.
The screened enclosure in which a parallel-plate
line is operating behaves as a cavity resonator [25]
with frequencies given by:
J
V(a/x)2
+ (b/y)2 + (c/::l
7.15
120
150
100
c:
~.g 100
~~
.....I
2VJi8
where a, b aQd c are integers (one of which may be
zero) and x, y and z are the dimensions of the
cavity, with f1 the permeability of free space and 8
the permittivity of free space. The screened room
in which the experiments were conducted was
6.7 x 2.6 x 2.2 m
and
had
a
fundamental
resonance at 62 MIlz. A 10 V 1m field calibration
of the line was therefore subject to progressive
changes above this value as the modes set up in
the screened room interact with the line, see
Figure 7.25. By placing RF absorbing material in
and around the line, together with a stack of
wN
~ 25
.....I
== _1_
E
~~
<co.
O-.S
w
ex:
83
n
.....
w
line
~
80
60
(j)
50
.....
...J
0
40
>
OL-0.1
--'1
20
.....Io-_ _
10
~
30
_
____I
100
FREQUENCY MHz
Figure 7.24
Variation oj line input impedance with
Jrequency, with EUT present and absent.
- - - - with EUT
- - - without EUT
0
1
10
100
500
FREQUENCY MHz
Figure 7.25
Parallel-plate line calibration: field
strength Jor constant input voltage, without
absorbent material Jor damping
USE OF ANTENNAS FOR RADIATED SUSCEPTIBILITY TESTING
123
are called TEM cells. They are however usually
quite small and can only be used for susceptibility
testing at component or board level.
SCREENED ROOM"
___ RF ABSORBING BLOCKS
1-2.23 m
7.12 TEM cells
I
PLATE LINE
i
I
I
I
1.9 m-:----+-J~-2.6 m
7.12.1 Basic construction
1 1 - - - 1 a i..:af-.·
i
I
I
I
~I~
DOOR
1.3m
··~i,~
I \
ABSORBER
STACK
1-----------6.7 m - - - - - - - - -
Figure 7.26
Disposition oj RF absorbing blocks around
parallel-plate line to control standing waves
in screened room
absorber at a specific location in this particular
room, shown in Figure 7.26, it was possible to
control the interaction between the room and the
line to produce the field strength calibration for a
constant 50W input power shown in Figure 7.27.
While there are still variations in the plot, they
are much reduced over the original disturbances
in Figure 7.25 and show the line being useful up
to almost 500 MHz.
These examples of the use of parallel-plate transmission lines indicate the type of effects which the
EMC test engineer must be aware of when using
them to perform radiated susceptibility testing. In
general, these efficient and economical devices are
best suited to testing small objects at high field
strengths, with simple lines being limited to
frequencies below about 30 MHz. There are more
sophisticated transmission-line devices which are
totally enclosed, operate up to higher frequencies
and can be used outside a screened room. These
120
LU
z
~
80
J:
o '-Q)
.....
~Q5
60
o
40
E
a:
..............
(f)~
0
..J
LU
iI
>
20
0
7. 12.2 erawford cell performance
Because the cell is based on a coaxial line with an
expanding cen tre conductor surrounded by a
carefully designed tapered rectangular conducting
box it has an almost constant impedance for
frequencies up to around 1 GHz. Figure 7.28
shows the construction of a Crawford Cell and
indicates the small volume into which the EUT
can be placed. Keiser [29J gives the characteristic
impedance of a square section Crawford cell as
Z ==
100
:::i
A TEM cell is constructed by gradually expanding
the size of a coaxial transmission line to dimensions
which are large enough for a small EDT to be
placed between the inner and outer conductors
without significantly altering the properties of the
line.
The Crawford cell [26-28J was designed by M.L.
Crawford at the National Bureau of Standards in
the USA as a means of establishing standard
uniform electromagnetic fields in a shielded
environment [29]. Compared with a parallel-plate
line the Crawford or TEM cell has two
advantages: operation at higher field strengths for
the same input power, and operation up to higher
frequencies. TEM cells have the disadvantage that
they can only accommodate small objects for test
without being scaled up to sizes where the SWR
becomes a problem. 'Typical sizes for test objects
are 15 x 5 x 10 cm and are much smaller than
those which can be tested in open parallel-plate
lines.
1
10
100
500
FREQUENCY MHz
Figure 7.27
Controlled field strength obtained in
parallel-plate line Jor 50 W input power
with absorber material in place around line
and in screened room
ft;[
94.15
we]
b(1 - t/ b)
ohms
7.16
+ 0.088 £1'
where Z == characteristic impedance of line,
C == capacitance/unit length (pF /cm), £1' == relative
permittivity, and dimensions w) band t relate to
those of the cell componen ts shown in Figure 7.29.
Keiser [29J also gives figures for typical cut-off
frequencies above which more complex modes
will propagate in the cell. These are given in
Table 7.5 as an indication of the upper limit of
simple TEM operation for a typical line (with
C == 0.087 pF /m.).
Other investigations into
TEM-cell cut-off frequencies have also been
reported [30, 31].
124
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
TEST VOLUME
At frequencies well below the cell cut-off frequency
Spiegel et al. [32J have calculated (using
quasistatic approximations) the electric field
strength as a function of position above and below
the centre conductor or septum. These calculations were made for the 30 cm-square TEM cell in
use at the National Bureau of Standards, and
then compared with measurements which had
previously been made. The plots in Figure 7.30
show how the field varies across the working
space above and below the septum.
7.12.3 Wave impedance in TEM cell
Top view
- - - - - - - - - - . , . .-----OUTER BOX
INNER PLATE
\
OUTPUT CONNECTOR
Side view
~6~~~~~L - :j~TVOLUME
SEPTUM PLATE
Figure 7.28
INSULATING LOW LOSS SPACERS
Ijpical Crawford cells
Reproduced by permission or Amplifier Research
b
i
+I~---I
TI
OUTER BOX
SEPTUM PLATE
I
-w~·1
1--
1--1-- -
}'igure 7.29
b
7.12.4 Field distortions in TEM cell
------.tal
Cross section dimensions of square section
Crawford cell
Table 7.5 Dimensions and cut-offfrequencies of a
Crawford cell
b
w
cm
150
50
30
cm
124
41
25
Cut-off
frequency
cm
0.157
0.157
0.157
Because the structure of a TEM cell is so simple
and the wavefield is well behaved below the
cu t-off freq uency, few engineers have investigated both the electric and magnetic fields
present in the working space [32J. This has led
to the assumption that the E-field can be
determined from a consideration of the cell as a
parallel-plate capacitor and the H-field is equal
to the E-field value divided by 377 ohms. Thus
the H-field determination relies on the relationship
between E
and H
for
free-space
propagation. For most applications this rough
treatment is sufficient,
however at low
freq uencies this approach is progressively unsatisfactory [32].
The issue of wave impedance in either a TEM
cell or a parallel-plate line is an important one for
the EMC engineer, as the value of the H-field
components can have a significant effect on the
induced currents in the EDT, and thus affect its
susceptibility. If the same object were to be tested
in apIa te line and in a free field at the same
frequency and E-field strength, there is no
guarantee that the immunity of the object to the
two wavefields would be identical, as the H-field
in the line may not be related to the E-field value
by the impedance of free space.
MHz
100
300
500
When an EDT is placed into the TEM cell it
distorts the field in the line and loads it at some
point along its length. Because the field strength
changes from the unloaded condition it is then
difficult to know what value to ascribe to a
susceptibility which might be observed for the
object under test. Foo et al. [33J have performed
2D finite element EM computations for TEM
cells with various dielectric and conductive
objects inside them. As a guide to the percentage
change in E-field which will occur in a TEM cell
the calculations are performed around a semicircular cylindrical EDT, and result in the data
shown in Figure 7.31.
USE OF ANTENNAS FOR RADIATED SUSCEPTIBILITY TESTING
o _-r---.--...,..-.,...-r---r--r--r-......--r--I"'"""""T--'--""-"'"
:c
0.1
0.2
I-
~
~
CROSS SECTION OF A
SQUARE CRAWFORD CELL
0.3
30em-....- - - -
0.4
~
0.5
Cl
0.6
~ 0.7
~ 0.8
u:I
u:
125
Figure 7.30 Variation offield
strength with position inside
square cross section Crawford cell
26.25 cm
§
a.
22.5 cm
~.8 0.9
«i=
rrJ
10
0
.
1.1
1.2
1.3
1.4
a::
18.25 cm
SEPTUM PLATE
---- --------
15em
--C::=::::=:::J
1.4
~
1.3
1.2
<:)
rIi
11.25 cm
1.1
~ E 1.0
CfJ.2 0.9
g
gW
7.5cm
0.8
C/)
iI ~ 0.7
UJ 03 0.6
2::.0
0.5
rrJ
0.4
0.3
0.2
~
a::
3.75cm
Oem
30 em
0.1
I
o
I
wide---~~I
I
6 8 10 12 14 16 18 20 22 24 26 28 30
2 4
DISTANCE FROM SIDE WALL
The plots show the percentage field distortion
at the centre of the cell (above the septum) for
cylinders of various radii and dielectric
constants. The upper heavy curve is for a
I
1-----0
conducting cylinder and this result is most
appropriate for the type of metal box object
which is usually subjected to EMC susceptibility testing. I t is clear that significant
distortions of about 50% of the assumed field
value are encountered by a conductive object
which is 1/4 the height of the working part of
the cell.
r-
;::)
w
~
~
%
7.12.5 Other uses of TEM cells
124
o
0-
r-
z
100
(5
SEPTUM PLATE
0-
~
78
o
....J
W
u::
w
58
conductor
~
z
o
41
i=
0:
o
~
CS
#.
33
20
25
15
10
8
0.15 b
.2 b
.25 b
.3 b
.35 b
.4 b
NORMALISED RADIUS OF CYLINDER r
Figure 7.31
Effect oj EUT in TEM cell.
Inset: upper half oj TEM cell
.45 b
In addition to the conventional use of TEM cells
for high field strength wide bandwidth EMC
susceptibility testing of small items, these devices
are used for other purposes. The measurement of
the shielding properties of materials including
gaskets has been undertaken using TEM cells
[34, 35]. Special TEM cells have also been used
to test the susceptibility. of circuits on printed
circuit boards to fields with deliberately high
wave impedances to sim ula te the conditions
pertaining to near field coupling at circuit board
level [36]. TEM cells are especially useful in the
field of investigating the biological effects of
intense EM radiation [37, 38]. These cells can
generate accurately known fields at very high
levels using simple apparatus and for a
reasonable cost. A graph of field strength against
input power for a cornmercial TEM cell [52J is
given in Figure 7.32.
126
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
7.13 GTEM cells
w
0-
U5 E
z->
J:-
..... w
C)~
z::>
w-J
0:
0
~>
ot...Jw
WW
u::t-
1000
900
800
700
600
500
400
300
200
100
.1
7.13.1 Description
50 100
10
5
500
INPUT POWER ( WATTS)
Figure 7.32
Field strength against input RF power for
commercially available Crawford cell.
Specification AR TC0500: frequency
range) de to 500 MHz)· power input)
maximum) 500 W)· impedance of cell)
50 ohms)· VSWR) maximum) 1.2:1 to
250 MHz) 1.4:1 to 500 MHz)· cell total
width) 1 m)· cell total height) 30 em)· cell
total depth) 50 em)· septum depth) 37 em)·
maximum dimensions of device under test
(w x h x d)) 15 x 5 x 10 em
Reproduced by permission of Amplifier Research
7.12.6 Asymmetric TEM cells
Asymmetric TEM cells have been designed [40J to
increase the working space where the EUT can be
accommodated for a given overall cell size. In a
normal sg uare cell the E UT height is limited to
about one sixth of the cell overall height. The
septum is offset in the asymmetric design as
shown in Figure 7.33 leaving a greater space
beneath it. The field distortion that is produced
as a result can be mitigated by making the cell
wider, but these changes usually result in compromising the cell cutoff freg uency.
The construction and operational parameters
associated with TEM cells have been discussed, and
examples offactors which EMC engineers should be
aware of, such as bandwidth and field distortion,
have been presented. These low cost, simple to
operate devices are widely used for EMC susceptibility testing and for other related purposes. They
can produce high field strengths over wide bandwidths but are usually limited to small test objects.
The GTEM or gigahertz transverse electromagnetic mode cell is a high-frequency variant of the
TEM cells discussed. It is a single-taper
development of an asymmetrical TEM cell with an
offset septum plate for increased working volume.
I t also has both a current load connected to the
septum and distributed wave termination in the
form of a RAM wall at the end of the enclosing
taper. I t may be viewed as a careful combination
of aspects of a TEM cell and an anechoic
chamber. l'hese features endow the design with the
useful properties of a large working volume and
high freg uency performance in addition to the
normal features of Crawford-type TEM cells.
7.13.2 Typical construction
The concept has been the subject of a patent [41 J
and has been variously reported by the
originators [42-44 J. A vertical cross section of a
GTEM cell is shown in Figure 7.34. It is
constructed as a tapered section of a rectangular
50 ohm transmission line. At the apex of the cell is
a precision made transition from coaxial cable to
the transmission line.
The travel time for any signal path from the
source to the load at the opposite end of the cell is
the same, as the RAM-loaded end wall is curved.
Also in a GTEM cell, there are no shape discontinuities, such as exist in Crawford cells, which can
act as sources of diffracted non-TEM radiation.
As th-e radiation travels along the line, the
strength of the E-field varies as l/distance in a
similar manner to that for a spherical plane wave.
The offset septum plate is terminated by a
distributed noninductive resistive load across the
large end of the cell and provides a return path
for the current via the conducting outer case.
CLOSED METAL
RESISTIVE MATCH FOR
RETURN CURRENT ON SEPTUM
END WALL
OFFSET SEPTUM
OFFSET SEPTUM PLATE
---+I
I
300
750
4
IN/PUT CONNECTOR \
IT
T
I
~
r 60°-+-9°°+6001
~
t--
-----j
1350
Example of asymmetric TEM cell
\
\
\
720
all dimensions in mm
Figure 7.33
r
\
~ \
\
\
A TAPERED 50 n -----TRANSMISSION LINE
~ 15% SECTOR OF
SPHERICAL WAVE FRONT
( ie. almost a plane wave I
Figure 7.34
RADIO ABSORBENT MATERIAL
- acts as a high frequency load for the wave
Schematic diagram of GTEM cell
USE OF ANI'ENNAS FOR RADIATED SUSCEPTIBILITY TESTING
The performance of a GTEM cell with aIm
maximum floor to septum height produced within
Asea Brown Boveri by Hansen et al. [43] is shown
in Figure 7.35. The flatness of the E- and H-field
I
l-
e:>
z
1
T
W
0::--1
1---1
(J)W
E FIELD
-
~W
L1.1-
we:>
>z
--
-
H FIELD
~-
-- - - - ..-..-.
....
~
--I
W
0::
10
100
1000
FREQUENCY MHz
SEPTUM HEIGHT - 1 m
Figure 7.35
Flat response oj E- and H-Jields in
GTEM cell
1.20....---------,.------------.
SEPTUM
"
1.00
~ 0.80
e:>
jjj
I
frequency response of ±3 dB is outstandingly good
over the frequency range up to 1 GHz. The ± 1 dB
E-field contour for aIm GTEM cell is shown in
Figure 7.36 with an indication of the size of an
EDT which has dimensions of 1/3 of the septum
height and cell width. It is clear that an EDT of
this size is immersed in an almost uniform field.
7.13.3 Power requirements
i
aO 10dB
--1~
---
1-000..
127
The field strength which can be generated in a
GTEM cell as a function of input power and cell
size has been determined [43] and is shown in
Figure 7.37. For aIm final septum height it
required just less than 1 kW to generate 200 V/n1
over the test object volume with a uniformity of
±l dB. Very large GTEM cells with final septum
heights of 5 m have been constructed for
automobile EMC testing [43] but it can be seen
by extrapolating from Figure 7.37 that RF
amplifiers capable of delivering more than 10kW
are needed to produce high field strengths
(200 V 1m) in such a large volume.
A three-dimensional view of a GTEM cell
suitable for immunity testing of medium sized
electronic units with sides up to 50 cm long, such
as PCs (personal computers) and peripherals, is
shown in Figure 7.38.
0.60
--J
--J
+-1 dB
envelope
W
() 0.40
Offset septum leaves a large
volume for testing
RF TRANSPARENT
END WALL _____
0.20
0.00
SEPTUM LOAD
1--
RF SEALED OUTER STRUCTURE
eliminates leakage
_
o
-1
CELL WIDTH
Figure 7.36
Field uniformity contours in G TEM cell.
Inset: An EUT with dimensions oj cell
working size
\
i
WAVE LAUNCHING SECTIONS
for both CW & pulsed testing
INPUT CONNECTOR
1,000'
Figure 7.38
o::E
w ....
6>
i!: ~
o=>
ffi5
0::>
1-0
ClJz
S2
9
PYRAMIDS MADE FROM
RADIO ABSORBENT MATERIAL
• act as a good wideband load to wave field
General viezRJ of G TEM cell with E UT in
place.[or testing (G T EM is a trademark of
Emco)
100,
7. 13.4 G 1-'£ M cells for emission tes ting
10
~g§
u.~
1 ......_ ......._ ........_ - - a . _ - - - I t . . . -
o
0.5
1
1.5
2
_
2.5
3
3.5
INNER CONDUCTOR HEIGHT m
Figure 7.37
Field strength as Junction oj working
volume height in G TEM cell Jor various
input RF power levels
It has been suggested [43, 44J that GTEM cells
can also be successfully used for radiated emission
testing of suitably sized objects. The EDT is
positioned as for a susceptibility test but the input
connector to the cell now becomes the ou tpu t
which is conl)ected to an EMI meter. The
sensitivity of the cell used in this way is reported
to be high [43J and successful measurements have
been made and compared with VD~ and FCC
measurements made on OATS (open area test
sites) .
128
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
The great advantage of making emiSSion
measurements in this way is the absence of
ambient signals which so often confuse open-site
measurements and slow down the testing. Using
a GTEM cell also obviates the need for the
large
number
of
measurement
antennas
described in Chapter 6, and as no antenna
changes are necessary the testing is accomplished
more quickly. Further work will need to be done
to gain general acceptance for this GTEM
method of emission measurement, but it would
appear to be a very promising cost-effective
technique.
7.14 References
2
3
4
5
6
7.13.5 Pulse testing
Because the GTEM cell has such a flat frequency
response over a wide band it is ideally suited to
making distortion-free fast pulse measurements.
These cells can be used to propagate simulated
NEMP waveforms over test objects at full threat
field levels as required by MIL STD 461 C test
RS05
(50 kV 1m). The peak field strength
obtainable as a function of final septum height for a
lOOkV input pulse amplitude is given in Figure 7.39
[44J.
7
8
9
10
-
1000
E
11
>
~
w
::>
-'
~
~
w
12
100
D-
C
-'
w
u:
o
a:
I-
~
W
13
10
0.5
--11-_ _- - - - ' ' _ _
2
14
_
3
4
5
TEST CHAMBER HEIGHT m
Figure 7.39
Pulsed E-Jield strength against test volume
height Jor pulse generator amplitude oj
lOOkV
15
16
The GTEM cell is the result of progressive
develop men ts in design from simple parallel-plate
lines, through TEM Crawford cells and
asymmetric TEM cells combined with some
properties of RF anechoic chambers to yield a
multipurpose reliable piece of test equipment for
modern EMC testing. Its advocates point out that
it is less costly and more useful than anechoic
chambers for small test items. I t appears to be a
very versatile equipment which may become
widely used in future years.
17
18
19
20
'Reference data for radio engineers'. (Howard W.
Sams, 1977) p. 27-8
'Reference data for radio engineers'. (Howard W.
Sams) p. 28-20
BULL, D.A. and CARTER, N.J.: 'Testing civil
aircraft and equipment to the new external RF
environmental conditions'. Proceedings of IEEE
symposium on EMC, 1990, pp. 194-203
JOFFE, E.B.: 'Are RS03 limits in the HF band
realistic?' Proceedings of IEEE symposium on
EMC, 1990, pp. 196-201
DEF STAN 59-41, DCS02, Ministry of Defence, UK
CARTER, N.J., REDMAN, M. and WILLIS, P.E.:
'Validation of new aircraft clearance procedures'.
Proceedings of IEEE symposium on EMC, 1988,
pp.117-124
KERSHAW,
D.P.
and
WEBSTER,
M.J.:
'Evaluation of the bulk current injection
technique'. Presented at IEEE symposium on
EMC, 1990, 14 unnumbered pages not bound into
proceedings
BURBIDGE, R.F., EDWARDS, D.J., RAILTON,
C.J. and WILLIAMS, D.J.: 'Aspects of the bulk
current immunity test'. Proceedings of IEEE
symposium on EMC, 1990, pp. 162-168
Model EFG3 E-field generator operating instructions. Instruments for Industry, Inc, Nj, USA
Model AT 3000 E-field generator, Amplifier
Research, 160 School House Rd, Souderton,
PA 18964-9990, USA
WHITE, D.R.J.: 'Handbook series on electromagnetic interference and compatibility, volume 2:
EMI test methods and procedures'. Don White
Consultants, Germantown, Maryland, USA
MIL ST'D 462 notice 3 (EL). Army Department,
Washington, DC 20360, USA 9 Feb 1971, pp.118-124
E-field sensors EFS 1/2/3. Instruments for Industry
Inc, Nj, USA
DIN 45 305 part 302: Methods of measurement on
radio receivers for various classes of emission; Methods
of checking the immunity fronl interference fields of
radio receivers. Beuth-Verlag, Berlin 30, Germany
ANKE, D. and BUSCH, D.: 'Parallel-plate
antennas: field distortion caused by test objects'.
Institution of Electronic & Radio engineers, 1985,
55, (6) pp. 210-216
'Reference data for radio engineers'. (Howard W.
Sams) p. 24-22
'0.8 m parallel-plate line'. ERA report 80-135, ERA,
Leatherhead, Surrey, UK
BRONAUGH, E.L.: 'Simplifying EMI immunity
(susceptibility) testing in TEM cells'. Proceedings
of IEEE symposium on EMC, 1990, pp. 488--491
MARVIN, A.C. and THURLOW, M.: 'A 1 m
separation strip line using tapered impedance
transformer sections'. British Aerospace Dynamics,
Filton, Bristol, UK
'Design handbook, electromagnetic cOlTIpatibility'.
Department of Defense, Washington DC, USA,
AFSC DH 1-4
USE OF ANTENNAS FOR RADIATED SUSCEPTIBILITY TESTING
21 PORTER, R.S.: 'A high field strength low cost
component susceptibility test facility'. Proceedings
of IEEE symposium on EMC, 1990, pp. 227-231
22 MADDOCKS, A.J.: 'Draft specification for the
measurement of immunity of road vehicle anti-lock
braking system to electromagnetic radiation'.
Project
report
5043/4R6/4,
1983,
ERA,
Leatherhead, Surrey, UK
23 'Uniform provisions concerning the approval of
vehicles with regard to braking'. ECE Reg. 13/05,
UN Economic Commission for Europe, 1988
24 'On the approximation of the laws of member states
relating to the braking devices of certain categories
of motor vehicles and of the trailers'. EC Directive
71/320 amended by 85/647EEC, Commission of the
European Communities, 1985
25 HARRINGTON, R.F.: 'Introduction to electromagnetic engineering'. (McGraw-Hill, New York,
1958)
26 CRAWFORD, M.L.: 'The generation of standard
EM fields using TEM transmission cells'. IEEE
Trans., 1974, EMC-16, p. 189
27 CRAWFORD, M.L.: 'Measurement of EM
radiation from electronic equipment using TEM
transmission cells, NBS international report 73-303,
1973
28 CRAWFORD, M.L. and WORKMAN, j.L.:
'Using a TEM cell for measurement of electronic
equipment'. NBS technical note 1013, 1979
29 KEISER, B.: 'Principles of electromagnetic compatibility'. (Artech House, 1987, 3rd edn.) p. 346
30 HILL, D.A.: 'Bandwidth limitations of TEM cells
due to resonances'. ]. Microwave Power, 1983, 18,
pp. 182-195
31 WElL, C.M., JOINES, W.T. and KINN, j.B.:
'Frequency range of large scale TEM mode
rectangular strip lines'. Microwave ]., 1981, 24,
pp. 93-100
32 SPIEGEL, R.J., JOINES, W.T., BLACKMAN,
C.F. and WOOD, A.W.: 'A method for calculating
the electric and magnetic fields in TEM cells at
ELF'. IEEE Trans., 1987, EMC-29 (4)
33 FOO, S.L., COSTACHE, G.l. and STUCHLY,
S.S.: 'Analysis of electromagnetic fields in loaded
TEM cells by finite element method'. Proceedings
of IEEE symposium on EMC, 1988, pp. 6-8
129
34 CATRYSSE, j.: 'A new test cell for the characterisation of shielding materials In the far field'.
Proceedings of IEEE symposium on EMC, 1990,
pp. 62-67
35 BROWN, j.T.: 'Using TEM cells for shielding
performance evaluation'. Proceedings of IEEE
symposium on EMC, 1990, pp. 495-499
36 DAS, S.K., VENKATESAN, V. and SINHA, B.K.:
'A technique of electromagnetic interference
measurement with high impedance electric and low
impedance magnetic fields inside a TEM cell'.
Proceedings of IEEE symposium on EMC, 1990,
pp. 367-369
37 BLACKMAN, C.F. et at.: 'Induction of calciumion effiux from brain tissue by radio freq uency
radiation: Effects of modulation frequency and
field strength'. Radio Sci., 1979, 14, (6S), pp. 9398
38 HILL, D.A.: 'Human whole body radio frequency
absorption studies using TEM transmission cell
exposure system'. IEEE Trans. 1982, MTT-30,
pp. 1847-1854
39 TC 0500 TEM cell. Amplifier Research, 160 School
House Rd, Souderton, PA 18964-9990, USA
40 VERHAGEN,
V.H.A.E.:
'Analysis
of an
asymmetric TEM cell for immunity testing'.
Proceedings of IEEE symposium on EMC, 1990,
pp. 157-161
41 HANSEN, D. and KOENIGSTEIN, D.: Patent
CH 670 174 A5: Vorrichtung zur EMI-Prufung
electronischer Gerate, 1989
42 KOENIG·STEIN, D. and HANSEN, D.: 'A new
family of TEM cells with enlarged bandwidth and
optimized working volume'. Proceedings of 7th
international symposium on EMC, March 1987,
pp. 127-132
43 HANSEN, D., WILSON, P., KOENIGSTEIN, D.
and SCHAER, H.: 'A broadband alternative EMC
test chamber based on a TEM cell and anechoic
chamber hybrid'. Proceedings of IEEE symposium
on EMC, 1989, vol. 1, pp. 133-137
44 GARBE, H. and HANSEN, D.: 'The GTEM cell
concept; Applications of this new EMC test
environment to radiated emission and susceptibility
measurements'. Proceedings of IEEE symposium on
EMC, 1990, pp. 152-156
Chapter 8
Receivers, analysers and
•
nneasurennentequlpnnent
8.1 Introduction
Section 8.1.1 is discussed in two groups: that used
for emission testing and that used for susceptibility testing
This chapter discusses the types of electronic test
equipment commonly used in EMC emission and
immunity testing over the frequency range from a
few hertz to tens of gigahertz.
INSTRUMENTATION FOR EMISSION
TESTING
8.1.1 Outline of equipment
8.2 EMI receivers
EM C emission testing is carried ou t using a sensor
or pickup device connected to a receiver,
spectrum analyser or other item of measurement
equipment which gives a voltage reading that can
then be converted to the quantity being measured
via the sensor calibration or transfer function.
1'he receivers, or EMI meters as they are
sometimes called, are complex items of RF
technology which in some cases have been
especially designed for EM C test work.
Susceptibility testing requires the use of a range
of CW, modulated CW and pulsed signal sources.
High output powers are often needed and are
produced using broadband high-power RF
amplifiers. Other equipment which is commonly
used directly in RF susceptibility testing includes
directional couplers, power circulators, highpower RF broadband loads, diode detectors, RF
power meters and frequency meters.
The practising EMC test engineer must be
familiar with the performance capabilities and
limitations of all this laboratory electronic instrumentation, and be able to use it correctly to carry
out testing to a wide variety of EMC standards.
The managers of companies engaged in test
work should appreciate the sophisticated nature
of EMC test equipment and be able to evaluate
its technical merits, the capital outlay required,
probable life, calibration and maintenance costs
and reliability to make cost-effective investment
decisions. The customers of EMC test facilities
should be familiar with the type of instrumen ts
used to make measurements on their test
specimens and able to appreciate how the high
cost of this equipment contributes to the facility
tariff.
8.2.1 Design requirements
EMI receivers are frequency tunable audio, RF and
microwave variable bandwidth voltmeters which
can measure and display the absolute amplitude of
a complex unknown input signal. The receivers are
usually superheterodyne equipments which have
been designed carefully to measure the amplitude of
CW, broadband noise and impulsive noise signals
accurately using a wide range of intermediate
frequency and post-detector bandwidths. The key
design features of a typical midfreq uency range
(10 kHz-30 MHz) EMI receiver are
Wide tunable frequency range, up to three or
four decades
High sensi tivi tyflow noise figure, < 10 dB
(0.01 flV in 100 Hz)
Good input VSWR < 1.5: 1
Good gain flatness across band « ± 2 dB)
Good
absolute
measurement
accuracy
(uncertainty < ± 2 dB)
Built-in switchable calibration sources for CW
and impulse signals to enable substitution
measurements to be made
Good out-of-band signal rejection > 100 dB
(using inpu t bandpass and tracking filters)
Careful mixer design giving overload signal
warning and low harmonic distortion, intermodulation, LO leakage, image responses and
spurious signal responses of > 70 dB down
Wide-range input and IF attenuators with
coupled action
LO output with usable power> - 20 dBm
Low parameter drift with time/temperature
(e.g. frequency and amplitude)
Good dynamic range of 0-60 dB in a single
range, and 0-120 dB with attenuators
Good dynamic range with impulsive signals 060 dB with preselection
8.1.2 Groups of equipment
EMC test equipment, including that mentioned in
130
RECEIVERS, ANALYSERS AND MEASUREMENT EQUIPMENT
vVide selection of measurement IF bandwidths
1 kHz-10 MHz with known 3 and 6 dB
bandwidths and shape factors
Wide selection of post-detector bandwidths,
1 Hz-100kHz
Selection of detector functions
Peak
Slideback peak
Quasipeak
Average
BFO
FM
Manual and sweep frequency tuning
Automatic tuning via a digital data bus
Automatic
frequency
control
(AFC),
switchable
Selection of output ports (amplitude)
Linear IF
Log IF (0-70 dB)
Linear video (0-5 MHz)
Log video (0-5 MHz, 0-70 dB)
Panel meter
Audio output
Plotter ou tpu t
Data bus output
Selection of output ports (frequency)
Panel meter
Plotter x-drive
Panoramic display x-drive
(spectrum analyser display)
Remote control
All main functions and ou tpu ts should be
accessible via a common standard data bus
(e.g. IEEE 488)
The equipment should be rugged, lightweight
(man portable), battery powered (as an
option) and should have a good EMI-shielded
case (better than 100 dB) .
EMI meters which cover the low audio-frequency
range below 10 kHz and microwave receivers
above 1 GHz may not be able to satisfy all the
parameter requirements listed, as the circuit
INPUT
PORT
ep
131
VIDEO
OUTPUT
AUDIO
OUTPUT
VOLTMETER
L-BUFFERED
OUTPUTS
FREQUENCY
Figure 8.1
Simplified EMI receiver block diagram
designs will be different for these equipments froD1
the midrange HF jVHF jUHF instruments. For
example, it has been extremely difficult to provide
good front end preselection filters in a small
lightweight unit for the low frequency receivers.
The more complex input filtering and multiple
heterodyning designs used in microwave receivers
can affect the sensitivity, input VSWR and gain
flatness which may not be as good as the midfrequency range receivers.
The design of EMI receivers with all the
features listed above is a considerable task and
manufacturers must inevitably make compromises
between some of the design parameters. An
insight into the design process and some appreciation of the engineering which justifies the high
cost of these sophisticated receivers may be gained
by reference to Coney and Erickson [1 J.
A simple block diagram of a basic EMI receiver is
shown in Figure 8.1. A more detailed diagram of a
typical receiver is given in Figure 8.2 and details of
an RF. front-end based on a commercial receiver [2J
which makes use of a number of separate octavewide receiver modules is shown in Figure 8.3. These
modules are switched into the signal path to cover
the appropriate frequency being analysed. The
restricted bandwidth of the individual modules
pern1its a design with good out-of-band signal
rejection and intermodulation suppression.
Figure 8.2 Block diagram of
typical EMI receiver
PLOTTER
OUTPUT
x DRIVE
(FREQUENCY)
LINEAR
IF OUTPUT
LOG IF
OUTPUT
OUTPUT LEVEL
METER
Reproduced by permission
Corp.
or
Camel Labs
132
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
Figure 8.3 Example offront
end of commercial EMf
recezver
IF
OUTPUT
Reproduced by permission of Camel Labs
Corp.
' - - - - - - - « AFC
8.2.2 Selectivity and sensitivity
power, then
High signal rejection to frequencies other than the
one being measured is the key performance feature
of an EMI receiver or meter. The spectrum
presented to the input port is likely to be completely
unknown, and may contain a time-varying mixture
of high- and low-level narrow-band signals,
together with bursts of random and impulsive
noise. Without narrow bandpass or tracking filters
at the input to the receiver, the first RF amplifier or
mixer stage will be overloaded [1 J and a forest of
spurious signals will be generated, leading to an
inaccurate assessment of the spectrum.
A good review of the circuitry and operation of
EMI meters can be found in White (volume 2) [3J
and is not repeated here. I t is necessary however to
have some idea of the sensitivity which EMI
meters can achieve. Receiver sensitivity is defined
with reference to the equivalent noise power
translated to the receiver input port, i.e. the output
or indicated noise power divided by the receiver
gain for a given set of parameters such as
frequency, attenuation, IF and post-detector
bandwid tho The noise power is defined as
N == KTB x F
where N
==
Smin dBm == -114+FdB + 10log 1o B
For a 50 ohm input impedance,
SdB,uV
noise power in W
K == Boltzmann's constant,
1.38 x 10- 23 W IK/Hz
T == temperature of receiver front end
(typ. 21° C == 293K)
B == receiver bandwidth in Hz
F == receiver noise factor (a multiple),
F dB is the receiver noise figure
If the receiver sensItIvIty is defined as that signal
power which is equal to the referred input noise
==
SdBm
+ 107
8.3
Examples of receiver sensitivity against bandwidth
for various receiver noise figures are given in
Figure 8.4.
The narrowband sensItIvIty for a receiver is
defined with regard to the random or thermal noise
power referred to its input port as given in eqn. 8.1.
Such noise is incoherent and does not have a
predictable phase relationship between incremental
frequency components of the noise waveform. The
comparison of intrinsic receiver noise power and
random noise or CW inpu t signals results in the
definitions of S, the receiver sensitivity.
If the input signal is broadband coherent
>-
1--
20
-87
~s
!:: 0. 10
>-
-97 ~
(/)Z
rna
(/)0
8.1
8.2
a::ll')
UJ-
»
W::1,
i=
-107~
0
-117
ffi !g
-20
-127
0
w
OeD
~
'0
~E
-10
-137 a::
-30
-40
1 kHz
>
-L.-.--..J-147
10 MHz 100 MHz
..I.-_ _--I-_ _---L_ _
10 kHz
100 kHz
1 MHz
RECEIVER BANDWIDTH
Figure 8.4
Receiver sensity as function of bandwidth for
narrowband signals and various noise
figures. F == receiver noise figure
Reproduced by permisssion of ICT Inc.
RECEIVERS, ANALYSERS AND MEASUREMENT'
133
r:
50,-~-----~---,.----r-----
8.2.3.2 Quasipeak detector (various
i=
40
LU
30
rrhe function of this detector is to
an output
reading which correlates well with the
~..L
assessed annoyance when listening to discontinuous
impulsive noise which may be heard from a
broadcast radio receiver. There are a number of
different specifications for quasipeak
the
two most widely used are the ANSI
and
CISPR (16) standards. 1'he rise and fall times are
different and given in Table 2.5 in Chapter 2.
Graphs of indicated output amplitude as a function
of pulse repetition frequency for peak, CISPR,
ANSI and RMS detectors are given in Figure 8.6
for a 6dB bandwidth of 9kHz (CISPR 16) [5J.
'The equivalent graphs for the CISPR 120 kHz
bandwid th are given in Figure 8.7
Quasipeak detectors are almost
used for
EMC emission measurements of commercial
electronic equipment being tested to standards
such as US FCC, German VDE, British BS or the
harmonised European EN series of standards.
:>
(jj
Z
C/)
oJL-<.'J I ' u " ' J L L V ...
O:N
~~
u>
20
F =35 dB
F =30dB
LU-
~~ 10
0'0
Z
«
OJ
o
o
«
o0:
-10
OJ
F =25dB
F=20dB
-20 L..-_ _- ' -_ _--'100 Hz
1 kHz
10 kHz
F = 15 dB
F = 10 dB
F=5dB
F=3dB
L..-_ _- ' -_ _--I F = 0 dB
100 kHz
1 MHz
10 MHz
RECEIVER BANDWIDTH
Figure 8.5
Receiver sensitivity as junction of bandwidth
Jor broadband signals and various noise
figures. F == Receiver noise figure
Reproduced by permission of leT Inc.
impulsive noise, then there is a defined phase relationship
between
adj acen t
incremental
freq uencies. In this case, the receiver will measure
a different rate of increase of impulsive signal
power to receiver noise power as the bandwidth is
increased. This leads to an increasing sensitivi ty
to the coherent signal as the receiver bandwidth is
increased, provided that the signal bandwid th is
always greater than the receiver bandwidth.
White [3J gives the following definition of receiver
sensitivity to impulsive noise:
0:
o
I-
o
ILU
~tu
1- 0
~
5
-----AM~:===-_.-1!J1IJIIIIt
0 .....
I
-10
a:~
~«
UO
LUI-
-7+F
lOlogloB
8.4
tu~
~
o
This assumes that the coherent signal power In a
given bandwid th increases as the square of
bandwid tho Examples of receiver sensitivity to
coherent broad band signals as a function of
bandwidth and noise figure are given in Figure 8.5.
8.2.3 Detectors
In addition to the high sensItIvIty, high dynamic
range and good unwanted signal rejection, EMI
receivers have a number of special detectors
which meet the requirements of various EMC
standards and test specifications. The main types
of measurement detectors are as follows.
-40
....J
W
0::
10
100
1000
10,000
IMPULSE REPETITION RATE (Hz)
Figure 8.6
Output Jrom quasipeak (OJ?) detectors as
junction oj impulse repetition rate.
-6 dB bandwidth == 9 kHz
Reproduced by permission of ICT Inc.
0:
oI-
PEAK
o I----------------~_-_t
U
I-W -6
::::>1o..LU
1-0 -12
::::>~
0« -18
o:W
8.2.3.1 Peak detector
This function allows the measurement of the peak
value of a time varying signal to be measured
during a preset window or gate tilue and
displayed as the RMS value of an equivalent
sinewave. Typical gate times are in the region of
3 ms to 3 seconds. A brief discussion of the factors
which determine optimum gate times for various
measureluents may be found in Reference 4. Most
MIL STD 462 emission measurements for
example are made using a peak detector.
00.. -24
-30
1-«
°0
~I- -36
WW
0> -42
o..i=
-48
0:)
W
0:
-54
-60 ~_ ____L.
1
0.1
_ I _ _ - - - - - I - - - - - L - - - -.....
10
100
1000
IMPULSE REPETITION RATE ( Hz )
Figure 8.7
Output Jrom quasipeak (OJ?) detectors as
junction oj impulse repetition rate.
-6 dB bandwidth == 120 kHz
Reproduced by permission or ICT Inc.
134
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
8.2.3.3 Slideback peak detector
This function is available on some receivers and
enables the operator to manually set a threshold
level which causes the amplitude meter to read
when a corresponding signal level is encountered.
If the peak value of an incoming time varying
signal reaches this threshold an audible tone may
be sounded to attract the operator's attention. By
successively reducing the threshold level the
operator can determine the amplitude of the peak
signal level. By tuning the receiver he can ascertain
the frequency dependence of the peak signal. l'he
time-varying triggering of the slideback peak
detector by a complex signal can help the EMI
engineer to identify the source of some interference
signals to particular functions and circuits.
8.2.3.4 Average detector
This detector produces an output which is proportional to the average of the modulus of a sinusoidal
signal. I t is mostly used for determining the levels
of CW carrier signals and is sometimes called the
field intensi ty detector.
8.2.3.5 AMjFM detectors
Also included in most EMI receivers are a simple
audio AM detector and an FM detector with an
output bandwidth which may be up to 10 MHz
wide to assist the operator in identifying
modulation types and probable EMI signal sources.
8.2.~ Commercially available EMI
receIvers
There are a number of commercial EMI receivers
available and examples of frequency coverage
against model type are given in Figure 8.8. EMI
meters are complex receivers specially designed to
accurately measure a wide range of unknown
signal types. 'T'hey are expensive and several will
FREQUENCY
1 kHz
10 kHz 100 kHz 1 MHz 10 MHz 100 MHz 1 GHz 10 GHz 100 GHz
\1M 7
NMJ/27
I
I
NM 37 /57
NM67
EATON
ESH3
ESJp
I
ROHDE & SCHWARZ
8.3.1 Introduction
Spectrum analysers are somewhat complementary
toEMI receivers and many EMC laboratories will
use both equipments during development and
conformance EMC testing. The spectrum analyser
is an extremely versatile piece of equipment which
enables the EMC engineer to quickly gain an
overview of the nature of a signal or complete
emission spectrum. In contrast to EMI receivers
most
scanning
superheterodyne
spectrum
analysers have wide-bandwid th front ends with a
preamplifier or mixer as the first stage and with
only minimal lowpass filtering. This can make
them more prone to signal overload in the
presence of broad band impulse noise signals than
the more protected EMI receiver front ends.
The noise figure for a superheterodyne spectrun1
analyser at around 20-30 dB is usually higher than
that for an EMI receiver which may be in the
region of 6-12 dB. However, the advantages
offered by the much wider frequency span (and
lower cost) of the spectrum analyser must be set
against this lower sensitivity.
Unlike EMI receivers, spectrum analysers are
used in a wide variety of applications in electronic
and communications engineering: sales specifically
for EMC work form only a small fraction of the
total market. As interest in EMC has grown and the
need
for
cost-effective
multipurpose
RF
measurement instrumentation has increased, manufacturers have become more aware of the need to
supply spectrum analysers with preselectors and a
range of detector functions to enable these
upgraded equipments to be used for EMC
conformance testing to some regulations.
There are three types of spectrum analyser:
EMC30
EMC60
Figure 8.8
8.3 SpectrulTI analysers
8.3.2 Analyser types
EMC 11
ELECTROMETRICS
be req uired to cover the frequency range 10kHz
to 18 or 40 GHz. Many can be swept internally to
produce a spectrum display and almost all have a
standard digital interface bus through which they
can be remotely operated. They are however most
useful, not as a spectrum analyser, but for making
accurate and reliable measurements of specific
signals within a complex spectrum. This leads to
a level of measurement confidence which is
necessary to meet the EMC test standards laid
down by procurement or licensing authorities.
IFE~
Examples qffrequency coverage by
commercial EMI receivers
(i)
(ii)
(iii)
Frequency
scannIng
superheterodyne
receIvers
Con tiguous band pass filter banks
Digital signal capture and software Fourier
transform systems
RECEIVERS, ANALYSERS AND MEASUREMENT EQUIPMENT
The frequency-scanning receiver is by far the most
widely used spectrum analyser. One of the first
commercial equipments was produced by HewlettPackard in the early 1960s followed by the more
compact and capable 141 T series which came into
wide use after its introduction in the late 1960s.
Since that time the spectrum analyser has benefited
from the revolution in measurement instrumentation brought about by the introduction of microprocessors during the 1980s. There are a wide range of
excellent processor based synthesised LO analysers
available covering frequency ranges from 10kHz to
2 GHz and beyond with bandwidths as low as
10Hz. Such performance is available from a single
equipment and at a reasonable cost.
Any scanning receiver cannot detect more than
one frequency (bandwidth) at any instant and
this can result in problems when measuring
pulsed signals. I t is sometimes difficult to resolve
the difference between a multiple line spectrum
and a low repetition rate broadband impulsive
signal without extensive manipulation of scan rate
and bandwidth. In certain circumstances it may
be necessary to produce a spectrum display from
a single pulse (e.g~ NEMP) and this cannot be
achieved using a scanning-type analyser.
For crude single pulse spectrum analysis a series
of contiguous bandpass filters can be used which
produce a histogram-type spectrum display. With
the advent of very fast analogue-to-digital
converters and fast Fourier transform software it
has now become possible to capture a single pulsed
waveform and then compute its spectrum. There
are a number of commercial systems available with
time resolutions of about 1 ns [6]. Such analysers
are not commonly used in EMC testing at present
but with the increasing interest in interference
135
produced by switching and other low repetition
rate pulsed interference events these software based
analysers will find increasing use.
8.3.3 Analyser operation
A simplified schematic diagram of a typical
scanning heterodyne spectrum analyser is given in
Figure 8.9. An example of an analyser input and
first mixer sections which largely determine the
noise figure, dynamic range, intermodulation and
spurious responses is shown in Figure 8.10. In
general, spectrum analysers do not have such a
good noise figure as a purpose-designed EMI
receiver, with typical values being 20-30 dB for
HF jVHF equipments and higher than this for
microwave analysers. It can be seen in Figure 8.10
that with the input attenuator set at 0 dB for
greatest sensitivity, the first mixer is divorced from
the input port only by a small fixed attenuator and
a lowpass filter. When a broadband coherent
impulse signal is fed to the analyser input it is
possible to overload the mixer with only modest
signal amplitude levels. White [3J suggests that in
the limiting case, when the input signal is
produced by a very wideband fast-edged impulse
generator, a spectrum analyser may have little
usable dynamic range without a preselector.
In my experience, spectrum analysers when used
with care, noting their broadband dynamic range
limitations, are a most useful piece of equipment.
They are the real-time eyes of the EMC test
engineer, rapidly conveying the full spectrum of
information about the unknown signal being
measured. By tuning in to a single frequency of
interest and putting the analyser into a video signal
display mode it is possible to see the modulation
B lock diagram of
multiple-stage
superheterodyne
spectrum
analyser
Reproduced by permissiolJ of" Hewlett
Packard
INPUT
ATTENUATOR
LOW PASS
3dB
FILTER AITENUATOR
FIRST
MIXER
LOW PASS
FILTER
SECOND
MIXER
t
RF
r
.L
..1.
INPUT
1 tn 1
i
1sfLO.
'"
/
BAND PASS FILTER
2ndL.O.
NOTCH
FILTER
n
2ndlF
Figure 8.10 Spectrum
analyser wideband front end
OUTPUT
W~
Reproduced by permission of Hewlett
Packard
136
HANDBOOK FOR EMC TESTING AND MEASUREMENT
1Hz 10Hz 100Hz
1k
10k
1001<
1M
1G
10M 100M
3585 B
100 100G
~590 ~ I
8592 B
8566 B
Hewlett
Packard
TR 4172
I
Advan1est
M~
611A
MS620
MS68
MS 2802 A
MS710
Anritsu
FSA
I
FSB
Rohde &
Schwarz
Figure 8.11
Examples qffrequency coverage by
commercial spectrum analysers
the
display screen as an
display. This often enables the test
and customer's technical representative to
the source of an interference signal and
the culprit circuit. This leads to spectrum
used during development
testing.
of spectrum analysers lies with their
range, functional displays and
compact nature. The cost per octave covered is much
less than that of an EMI receiver and a good
spectrum
component of a
Modern
well
systems are
controlled for ease of
and data recording. Many are tailor-made
EMC test work with the inclusion of bandpass or
......,v.......
YYr·""'c.'plpr .... nrc and a range of IF bandwidths
and detector functions
MIL STD 461,
FCC and CISPR. The
covered by
hTcp'rc are shown
Figure 8.11.
has
been
in this chapter to
an overview of the properties of spectrum
and EMI meters of interest to those
with EMC
The design of
receivers is an extensive subject in itself and is
dealt with in a number of texts, for example
References 7 and 8, which El\1C test personnel
may find useful. Some manufacturers offer a
of
notes relating to receivers
which are also valuable in
EMI measurements [9-12J.
IJ_LLJllJ'J'.LLll-
'---'!J"v.L ....., ...... '-/.L.L
l- ...
JL ...... .:;;..
A bank of fixed bandpass filters can be switched
manually or automatically into the signal path
prior to the first preamplifier or mixer circuit. A
more advanced automatic tracking bandpass
filters based preselector is available with some
spectrum analysers, turning them into wide band
EMI receivers over the frequency range of 20 Hz2 GHz, which includes the frequency bands of
interest for FCC and CISPRjEN specifications.
One such system is offered by Hewlett Packard
[13J with the model 85685A. It contains both
tracking bandpass filters and preamplifiers covering
the frequency range 20 Hz to 2 GHz and endows
the spectrum analyser with 30 dB improvement in
amplitude measuring range [14]. Belding [15J
discusses the theoretical basis for spectrum analyser
preselection and explores the
measurernent
situations where its use is advantageous with
particular reference to FCC type open range testing.
Preselectors are also available for microwave
measurement receivers such as the EMC-60 with
an FE-60 [ 16J frequency extender allowing
coverage froIYl 18 to 40 GHz. The improved
dynamic range and reduced spurious responses
obtainable with the preselector are accompanied
however by an increase in the receiver noise
figure, owing to additional front-end components
and some increased signal attenuation in the
passband. Typical noise figures with and without
preselection are shown in Table 8.1.
Table 8.1 Microwave receiver noise figure
Direct
input
With
preselector
Frequency
range
dB
14
14
dB
20
23
GHz
18-26.5
26.5-40
'An 'A
' J ' t - ' l - ....lAA ... U .......
F-,
Preselectors and filters
Modern spectrum
can be equipped with
filters to reduce the problems
wide bandwidth out-of-band
8.4.2 Bandlimiting filters
Individual filter units are used in EMC testing for a
variety of purposes. They are often built to be easily
connected into the coaxial line from a sensor or
antenna to a receiver or RF voltmeter and may be
lowpass, highpass, bandpass or bandstop. These
filters can be used to bandlimit spectra containing
small signals of interest in the presence of large
signals, to achieve the best receiver sensitivity and
linearity. Tunable narrowband rejection filters
[17J are sometimes used to reduce the dynamic
range of signals containing high-level carriers or
other narrowband emissions so that lower level
signals can be investigated.
Lowpass filters are used for example in test configurations for l11ethods CS-Ol, CS-03, CS-04, CS-05,
CS-08 and RS-04 of MIL STD 462. Commercially
available filters of this type [18J can have stopband
RECEIVERS, ANALYSERS AND MEASUREMENT EQUIPMENT
floor levels of better than 100 dB and can be
obtained with typical cut-off frequencies and
-100 dB frequencies as shown in Table 8.2.
Table 8.2. EMI measurement filters (lowpass)
Cut-offfrequencyf
-100dB frequency 3f
MHz
MHz
0.1
0.3
0.2
0.6
0.5
1.5
1.0
3.0
2.0
6.0
sequence repeats up to a cut-offfrequency of 50 MHz
Highpass filters are needed for methods CE-O 1
and CE-02 of MIL STD 462 to eliminate the
fundamental
power
line
frequencies
and
harmonics which otherwise would saturate or
destroy EMI receiver front ends. Typical filter
response curves are given in Figure 8.12 where it
can be seen that the two lowest frequency filters
provide 100 dB of attenuation to 50/60 Hz and
400 Hz mains power frequencies, respectively. All
filters used for bandlimiting signals before the
input to an EMI receiver are matched 50 ohm
devices and usually have coaxial connectors.
Bandpass filters are often used for isolating a
known frequency of interest from a spectrum with
high-level adjacent noise bands so that the
receiver or spectrum analyser can be adjusted for
maximum sensitivity, linearity and suppression of
spurious responses. It is important for the EMC
engineer to have access to a range of high q uali ty
filters for the purposes described to avoid the
pitfalls of making measurements on signals that
cause the measurement instrumentation to display
false amplitude data about the spectrum being
CD
-20
"0
0
-40
--I
Z
0
t=
-60
a:
w -80
Cf)
8.5 Itnpulse generators
8.5.1 Description
An impulse generator is a device which produces a
series of very short su bnanosecond-d ura tion pulses
with a variable pulse repetition frequency of
typically 50 Hz-10kHz to yield a flat wide band
pulsed RF spectrum of known spectral density
measured in dBIlV/MHz. Impulse generators are
used in EMC testing for a variety of purposes [19]:
Broadband calibration of EMI receivers or
spectrum analysers
Shielded structures attenuation measurement
'Transient
testing of devices
such
as
information technology equipment
Determination of filter frequency responses
Circuit coupling or crosstalk measurement.
The main use of impulse generators with a
calibrated output is as a secondary calibration
standard for EMI receivers. The frequency
coverage of an impulse generator can extend from
a few hundred Hz to 1 GHz with a spectral
flatness of ± 1 dB. The output level is usually
adjustable in 1 dB steps up to a value of above
100 dBIlV/MHz.
8.5.2 Design
Rc
~
-100
100
Figure 8.12
investigated. Instrumentation can be overloaded,
or operate in a nonlinear manner when
confronted with an unknown and complex
spectrum containing a mixture of high and lowlevel CW and impulse signals. The ability to
insert bandlimiting filters and adjust the receiver
input attenuation provides an effective way of
ensuring that these errors are minimised.
The generator is normally designed to produce a
short pulse at a high-voltage level by alternately
charging and discharging a short length of coaxial
transmission line. Figure 8.13 shows a coaxial line
of about 10 cm length being charged from a stable
high-voltage source through a high-value resistor,
where
0
Cf)
Cf)
137
1k
10k
FREQUENCY Hz
100k
Example of the insertion loss of commercial
highpass filters (50 n coaxial) for use in
EMC testing. Solar type -7205
Reproduced by permission or Solar Electronics
» <:'0
with R c as the charging resistor and <:'0 as the line
impedance. The capacitance of the short length of
line and the charging resistor determine the
charging time constan t and the line charges to a
value Vc in that time scale. When the closing
switch, which may be a mercury-wetted reed
relay, is operated, the stored energy in t~1e transmission line is allowed to escape into the load
resistor (50 ohm) and a short voltage pulse is
138
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
Figure 8.13 rast discharge
coaxial line impulse
generator (a) Impulse
generator diagram
( b) Waviform and
spectrum from impulse
generator
50n
STABLE
HIGH VpLTAGE
SUPPLY
~
100V
OUTPUT SPECTRAL DENSITY
UP TO 100 dB Jl V / MHz
"FLATil PORTION OF OUTPUT SPECTRUM
>.....
U5
z
w
o
100 V , . . - - - - - · - -....
PRF ~ 100 Hz
frl~
0..-'
..... ~
0>
FOURIER
TRANSFORM
::::>0
ov""'"-----.......;;::::::11111.....
TIME
-t=:::.5 ns---
formed at the ou tpu t terminals. The pulse wid th is
determined largely by the length of the coaxial
line. White [3J gives the voltage spectral density
of the ou tpu t pulse as
where S(])
~
Vc
t
~
f
~
~
2 V:. t sin (n] t)
nit
V/Hz
8.5
signal spectral density
charging voltage in volts
pulse wid th in seconds
frequency
The first null value in the spectrum occurs at
]~
N
.... J:
..... w
0.«
~
--T
..J
«
Cl:
::::>0
S (] )
_ _11dB
IltHz.
If the pulsewidth is typically 0.5 ns long the first
zero is at 2 GHz. When] « lit the (sin n ]t) In]t
expression tends to 1 and
8.6
1-'his shows that at freq uencies well below the first
null the signal spectral density is flat with an
amplitude of 2 V:. t. Thus these impulse generators
are useful as calibration devices as the spectral
output can be accurately determined from simple
measurable quantities. It is possible to improve
the useful upper frequency of the flat part of the
spectrum by designing a mismatch peaking circuit
which increases the higher frequencies in the
en>
w::t
C)
«
~
~
4
•
FREQUENCY
Impulse generator
used to calibrate
receivers over
this frequency
range.
LINE SPACING
AT PRF
pulse. Using this technique it is possible to
produce reliable and cheap instruments with
spectral flatness of ± 1dB to above 1 GHz.
8.5.3 Use of impulse generators
Commercially produced impulse generators are
available as stand-alone equipments [20J or are
built-in to some EMI receivers [21 J. As
men tioned earlier the au tpu t swi tch from the
coaxial line maybe a relay. I t can be triggered to
close either linked to the power line freq uency, or
to a variable frequency source. If pulse-repetition
frequencies above a few hundred Hz are required
the switch is usually replaced by a solid-state
device such as a fast FET.
A good reliable impulse generator is essential for
the EM C test la bora tory. I t can be used to
calibrate and check EMI meters and spectrum
analysers for amplitude accuracy, spurious signal
generation and dynamic range com pression; or it
can be used to give a direct reading of equivalent
broadband signal strength by adjusting the
output to give the same reading on the EMI
meter as the unknown interference signal being
measured.
l'his
is
generally
known
as
measurement by substitution and is a very
accurate but slow method of measurement.
RECEIVERS, ANALYSERS AND MEASUREMENT EQUIPMENT
8.6 Digital storage oscilloscopes
8.6.1 Advantages of digital oscilloscopes
Some of the more comprehensive EMC immunity
tests such as those in MIL STD 461/2 (CS06, CS10/
11, RS05) and IEC801/BS6667 call for continuous
and transient stimuli signals to be imposed on the
equipment under test and monitored with a fast oscilloscope using a high-impedance probe or other
sensor. There are also conducted emission tests such
as MIL STD 461/2 CE05, CE07-1, SP-P-90203 [22J
and EN550 14/BS800 in which transient or very low
repetition rate fast burst type signals must be
measured. For most of these tests details of the peak
amplitude, waveshape and repetition frequency
must be measured.
Traditionally, oscilloscopes have been used to
measure the signal ofinterest which is usually superimposed on a power line waveform which may itself
have an amplitude of ± a few hundred' volts.
Triggering a conventional oscilloscope on the
wanted interference signal can present problems
especially ifits amplitude and position with respect
to the mains frequency are variable. Setting up an
oscilloscope to record a single transient event is also
usually difficult and requires considerable experimentation and takes up valuable time in the EMC
facility. It is difficult to produce a record with the
transient in the centre of the scan even with delayed
trigger circuits on standard oscilloscopes.
Permanent records of transients have normally
been made by photographing the screen, either with .
an open shutter and a single scan, or by writing the
trace on to a storage screen and then using a timed
exposure. Many of these problems are eliminated
when digital storage oscilloscopes are used and the
measurement and recording of transient waveforms
can be achieved quickly and accurately.
139
conductor switching and regulating circuits in
mains power supplies. In such cases the noise bursts
may be locked to the power line waveform; in other
applications the noise bursts may not be synchronised or may even occur randomly. The detailed
vvaveform within a burst is often complex and may
be rather variable but if examined closely it usually
has some distinguishing feature such as an obvious
oscillatory frequency generated by unintentional
inductance/capacitance, which may indicate the
source of the interference. Using conventional oscilloscopes it can sometimes be difficult to examine
individual time-expanded bursts in detail owing to
triggering and screen writing speed limitations.
Some conducted emission tests require the
exported spikes from an EUT to be measured
when the device is turned on or off or functioned
in some other way. Figure 8.15 shows a typical
measurement setup where a single transient must
be measured on top of the power line voltage. In
some cases, it is possible to use lowpass filters to
reduce the amplitude of the power line waveform
and obtain a better trace on a conventional oscilloscope. A digitising transient capture instrument or
digital oscilloscope is ideal to record this single
interference event. Figure 8.16 shows the product
EXPORTED TRANSIENT
NOISE BURST
/
DIGITAL TRANSIENT
RECORDER OR
OSCILLOSCOPE
EUT
producing
noise burst
when switched
VOLTAGE PROBE
on or off
INDUCTOR
8.6.2 Typical waveforms to be measured
Figure 8.15
Figure 8.14 shows typical recurrent noise bursts
which may be produced by poorly designed semi-
Measuring exported voltage spikes with
digital transient recorder
600----r----------.....----------TRANSIENT NOISE BURST
( with fine structure )
> 200
w
w
~
~
o
~
o
..J
o
III-I~"",,,,"'--#---~-""~--I"TIME ms
>
w
> -200
~
0..
z
::J
0
-400
-600
1O~s
Figure 8.14
Transient capture oj noise burst on mains
pouJer Line
100ms
1mS
10mS
100mS
DURATION OF TRANSIENT ENVELOPE
MAINS POWER WAVEFORM
Figure 8.16
Example of exported spike limits from
SP-P-90203
140
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
200 ms----...,
I
1+---0.9
I
I
I
w
C)
~
....
zw
J
...J
I
0
>
....
z
I
z
,
w
U5
«
a:
:::J
()
0.1
I
l-
I
> 200 ms
}'igure 8.17
~ 0.5+--+-+---------....
time
I
I
...1
I
Example of exported transients defined in
BS800. Individual impulses shorter than
200 ms spaced closer than 200 ms continuing
for more than 200 ms
Figure 8.19
Typical output waveform oj ESD generator
(BS6667 pt2)
Reproduced by permission of BSI
Reprod uced by permission of BS I
specific SP-P-90203 specification limits for
transients emitted from an avionics EDT in the
form of amplitude-time envelopes for AC and DC
supplies. The exported transients must lie within
these envelopes.
Confirmation of this requires that the worst-case
transient can be recorded over a time scale of microseconds to many hundreds of milliseconds. Other
examples of the type of lo"v repetition-rate noise
burst signals of interest in EN550 1/BS800 as emitted
from household electrical appliances can be seen in
Figure 8.17. This specification permits the use of a
disturbance analyser [23] which can measure and
record transient amplitude and occurrence data for
statistical analysis. Such instruments are complementary to detailed measurements of individual events
with digital oscilloscopes.
8.6.3 Recording injected pulses for
immunity testing
Fast-transient recorders are also used to monitor the
amplitude and waveshape of transients or spikes
being injected on to the power lines connected to an
EDT. An example of the signal which must be
injected in accordance with MIL STD 461B CS06
is given in Figure 8.18. The risetime of this spike is
around 2/ls which is relatively slow. Oscilloscopes
and digital transient capture instruments need to
be capable of recording risetimes much faster than
this. For example the risetime of the simulated
NEMP waveform used in MIL STD 461 C RS05 is
IOns and that for the ESD pulse specified in
IEC80 1/BS6667 is 5 ns. As an example, the ESD
wave shape is given in Figure 8.19.
8.6.4 Digital transient recorder
architecture
Digital transient recorders can be extremely useful
in EMC measurement. The advent of fast, reliable
ADC integrated circuits and inexpensive memories
has led to a number of instruments which for the
first time make the capturing of low repetition or
single-shot fast transients a simple procedure.
There are three types of waveform digi tiser:
(i)
(ii)
(iii)
transien t digi tiser with circular addressing
random interleaved sampling RIS digitisers
and
sampling digitisers.
400
CJ)
I-
w~
300
t::e
O:X
200
«g>
100 I-
~~
a:::Q)
0
g~
....J
0
>
w
0
:2Q)
;:)
w=
CJ)~
::i
a..
:2
«
w
~
-100 a:::
CJ)
5
10
15
20
25
TIME lIs
Figure 8.18
Example of injected spike waveform
MIL STn 461B CS06. Use left or right
ordinate whichever is less in particular
application
When armed the first type continually digitises an
incoming waveform and constantly overwrites a
block of memory from start to finish and back to
the start, in a circular fashion. When a trigger
pulse is produced the digi tisa tion con tin ues un til a
user-specified post trigger time has elapsed and
then the digi tisa tion ceases and the memory is
locked. The captured waveform complete with
pre- trigger information is read ou t from the
memory and displayed on a screen.
Instruments with a digital output bus can
download the data to a PC or direct to a plotter.
A typical instrument will have a sampling rate of
around 100-200 megasamples per second, a
RECEIVERS, ANALYSERS AND MEASUREMENT EQUIPMENT
repetitive signal effective sample rate of 4 GS/s, a
single-shot bandwidth of 100-300 MHz, an 8 to
12 bit am pli tude resolution and two or more
input channels. l'ypical instruments are LeCroy
9410, HP 54112D and Tektronix RTD710A.
Among the fastest single-shot digitisers currently
available is the LeCroy 7200 series with four
channels operating at 1 GS/s and an analogue
bandwidth of 400 MHz.
The RIS digitiser can yield improved waveform
resol u tion in some cases by sampling anum ber of
identical input transients at slightly different
stages in the waveform and then interleaving all
the data.
A sampling digitiser or sampling scope can only
work with a long train of identical pulses or a
continuous waveform. Under these conditions a
digitised waveform can be produced with an
effective bandwidth of beyond 30 GHz [24].
In addition to the types of instruments already
discussed there are some transient capture
equipments using special very fast waveform
storage techniques which can also provide a
digital output. The Tektronix 7250 can capture
and display a single transient waveform with a
SOps risetime and the Tektronix model SCD1000/
5000 has a time resolution of 5 psjpoint.
Some digitisers have built-in signal processing
capability and can quickly calculate the Fourier
transform of a captured waveform and display
them together on a single screen. Instruments such
as HP 5180T/U, Tektronix TD2301 and LeCroy
7200 series have this ability to convert from time to
frequency domain. These powerful instruments
have a great deal to offer the practising EMC
engineer or equipment designer who needs to
develop electronic products which can meet EMC
standards, as they can give a rapid insight into the
full nature of a wide range of interference signals.
An excellen t technical tu torial concerning the
fundamentals
of digital
transient
capture
instruments IS produced by LeCroy [25 J.
Inspection will demonstrate the capabilities
available and need for careful specification of the
requirements for instruments of this type before
purchase by EMC engineers, if they are to obtain
full advan tage from this technology.
8.7 AFjRF volttneters
When performing low-frequency conducted
susceptibility tests such as MIL STD 461/2 CSO 1
and CS02 it is necessary to measure the injected
signal voltage on the lines to the E UT wi thou t
loading them with a low impedance (e.g. 50 ohms
input of an EMI meter). I t is also inappropriate
and unnecessary to use expensive and sensitive
141
EMI meters or spectrum analysers fitted with
high-impedance probes to measure these signals
which often have an amplitude of a few volts
RMS. The preferred economical method is to use
a high impedance RF voltmeter which can
measure the required signal at a fraction of the
cost of using an EMI meter. There are several
factors which determine which type of AC
voltmeter is appropriate:
For conducted susceptibility tests on DC lines a
broadband AF /RF voltmeter can be used. There
are a number of designs using diode bridges,
crystal detectors and sometimes preamplifiers to
provide measurement from a few kHz to above
2 GHz and amplitudes over the range ill V to 10
volts. AF /RF voltmeters with both balanced and
unbalanced inputs are available. A useful
description of AF /RF voltmeter design techniques,
including explanation of average, RMS and peak
reading meters, crest factor and form factor has
been produced by Rohde and Schwarz [26J.
For measuring signals injected into AC power
lines a tuned AC voltmeter is req uired which can
filter out the power frequency and its harmonics
producing a measurement of only the injected
signal amplitude. These equipments often use a
combination of fixed frequency highpass filters
and a tunable bandpass filter with bandwidths as
low as 10Hz in the case of AF voltmeters.
The frequency range of _the test, e.g. audio
frequencies up to 50 kHz for MIL STD 461/2
CS01 and RF frequencies up to 400 MHz for
CS02, will determine the req uiremen t for differen t
AF and RF selective voltmeters. The use of a high
input impedance (> 100 k ohm/3-5 pF) frequency
selective RF voltmeter is shown in Figure 8.20 in
a MIL STD 461/2 CS02 test setup. When making
measurements on AC lines, care must be taken to
ensure that adequate power-frequency rejection is
embodied in the AF /RF voltmeter to enable the
correct amplitude of the injected susceptibility
signal to be measured. A range of selective AF /RF
voltmeters is commercially available from a
number of electronics instrument manufacturers.
8.8 RF power tneters
RF power meters fall into two types: ou tpu t power
meters and directional power meters. Output
power meters measure the RF power delivered to
the sensing head and display it either on an
analogue meter or on a digi tal display or via a
digital interface bus. The power meter sensor
head should have a very low SWR « 1.3: 1 [27J)
over a wide frequency range (up to 26.5 GHz) if
measurement uncertainties owing to reflected
power are to be minimised.
142
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
Figure 8.20 Use of highimpedance RF wideband
voltmeter in conducted
susceptibility testing.
Susceptibility limits are in
terms of both voltage and
current
measures susceptibillity
current
CURRENT PROBE
ACorD
POWER
INPUT
MIL STD 461 CS 02
TEST
Most RF power meter sensor heads are
constructed using one of two basic mechanisms
[28J: conversion of RF power to thermal energy
and measurement by thermocouple, and diode
rectification and measurement by a sensitive
voltmeter. In general, the first is used for
moderate to high power meters and the second
for detecting powers as low as 100 PW (- 70 dBm) .
In addition to their general use as measurement
meters, for checking the output power of RF
amplifiers for instance, these instruments are very
useful in performing semiautomatic EMC RF and
microwave radiated susceptibility measurements. In
such a test configuration the radiated field strength
at the EDT has been previously measured and
defined in terms of the forward RF power delivered
to the radiating antenna, see Figure 8.2l.
A power meter and a suitable directional
coupler, or a directional power meter [29J can be
used to measure the power to the antenna and
convey the level to a computer controller which
compares the measured value with the value
required to produce the nominated field strength
at that frequency. The controller then adjusts the
ou tpu t of the signal source to reach the required
power to be delivered to the antenna.
SOFTWARE
& DATA
EUT
measures
susceptibility-voltage
HIGH INPUT
IMPEDANCE
RF VOLTMETER
- wideband/ tunable
An automatic power measurement loop such as
described, can rapidly generate the correct field
strengths on the EDT as the frequency in the band
is being swept, and so increase the throughput and
productivity of the test house. Software can be
devised to ensure that at no time during the power
setting process does the resultant E-field on the
EDT exceed the required value at each frequency.
Users of EMC test facilities should look for the
ability to perform semiautomatic tests of this type
when choosing where to have their equipments
tested, as they are likely to obtain faster tests and
better value for' money.
8.9 Frequency m.eters
These instruments are not now used as widely as
they once were following the introduction of lowcost, reliable and accurate synthesised signal
sources that can be used in EMC testing. Such
sources are accurate to a few Hz in hundreds of
MHz. A frequency meter is however useful for
carrying out spot calibrations on signal sources
together with a spectrum analyser to check
harmonic purity. A modern spectrum analyser with
a synthesised LO can itself be used to measure
frequency to within a few Hz in a GHz and can
therefore be substituted for a frequency meter.
INSTRUMENTATION FOR
SUSCEPTIBILITY TESTING
8.10 Signal sources
8. 10. 1 Signal synthesisers
Figure 8.21
Automatic control offield strength in
radiated susceptibility test using RF power
meter
In the past, EMC testing has required a wide
range of signal sources to meet the frequency,
amplitude and waveshapes needed for susceptibility testing. Frequencies covered extended from
a few Hz to 40 GHz and a large number of
sources were required. Most early signal
RECEIVERS, ANALYSERS AND MEASUREMENT EQUIPMENT
generators did not benefit from synthesiser
technology and thus were subject to time and
temperature drifts and were also manually driven.
White [30] summarises the situation with regard
to nonsynthesised sweepers and power oscillators.
Modern synthesised signal sources can ~over very
wide frequency ranges and only a few instruments
are needed in a modern well equipped EMC test
facility. These highly capable equipments tend to
be expensive, and relying on so few sources to
cover the required frequency range can present a
significant problem when they are not available
owing to periodic calibration or malfunction, as
the ability to conduct a whole range of tests may
then be affected.
In specifying the requirement for suitable
synthesised signal sources for use in EMC testing
it is necessary to consider
Frequency range
Frequency resolution
Frequency stability
Maximum output power and attenuator range
Absolute level accuracy
Spectral purity
Settling time
Modulation capability AM, FM, pulse and
possibly phase modulation
Ease of programming and type of data bus
Case shielding against RFI
Size, weight, reliability and cost.
It is possible to cover the frequency range up to
1 GHz specified for immunity testing of
commercial electronics equipment with only two
signal sources. For example;
•
R&S APN 1 Hz-260 kHz, resolution 0.1 Hz
,[ < 20 kHz and 1 Hz f > 20 kHz, output
•
50 f.1V to 20 V
HP 8657A 100 kHz-I040 MHz,
1 Hz, output -143 to 13 dBm.
resolution
Coverage from 1 to 18 GHz can also be obtained
in a single equipment such as the HP 8672S
(100kHz-18GHz), resolution 1 Hz and 3kHz,
output 120 to +13 dBm (2 dBmf > 2 GHz).
For a full understanding of the variety of
synthesised signal sources available and their
suitability for EMC testing the reader should
consult a range of specialist instrument manufacturers. Figure 8.22 is a guide to the range of
typical synthesised signal sources which are
available.
8.10.2 Signal sweepers
Sweepers do not usually have the frequency
accuracy of synthesisers bu t can produce a
levelled output (within about 1 dB) as the
143
10Hz 100Hz 1 kHz 10 kHz 100kHz 1 MHz 10MH~ 100MHz 1GHz 10GHz 100GHz
1 MHz
AFG/U
260
APN
20
)3
SPN
SMG
1
SMGU/SMHU
2.16 4.32
SWM 02/05
Rohde & Schwarz
MG 440 E
20
0.5
MG 545 E
MG 649 A
.1
18
2
Anntsu
8904 A
332 58
600
11
8656 B
8644 A
86600
0.99
2.06
2.6
~
2
Hewlett Packard
Figure 8.22
8360 series
26
50 110
Examples of synthesised signal generators
frequency is rapidly swept between the ends of a
given band. The oscillators are usually voltage
tuned (varicap diode or YIG) depending on
freq uency, and the fast ou tpu t sweeps can be used
for spectrum/network analysis with couplers,
detectors and a suitable display. When manually
operated or used with long scan times (10-100 s) ,
sweepers can be used as the signal source for
susceptibility testing. Most are programmable and
they are usually less expensive than syn thesisers.
8.10.3 Tracking generators
These devices are variable frequency oscillators
with maximum output powers in the range of 0 to
10 dBm which can be locked to the centre
frequency of the measurement bandwidth of a
spectrum analyser and track its scan accurately
over the band of interest. This ability results in a
cheap scalar network analyser which can be used
by EMC engineers and equipment designers to
measure filter responses, cable crosstalk, shielding
efficiency, cable losses and antenna passbands and
correction factors.
When used with two current probes as shown in
Figure 8.23 this simple network analyser can yield
a great deal of information about the RF
coupling behaviour of a complex systenl of interconnected equipments, such as a distributed
mainframe computer installation, and can help
uncover frequencies at which radiated emissions
or susceptibilities are likely to occur. I t has been
shown that the RF common-mode cable response
in such a system is often closely correlated with
the radiated emission from them [31], as in
Figure 8.24. I t also indicates frequencies of
probable susceptibility.
144
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
Figure 8.23 Tracking
generator and spectrum
analyser used to measure
cable transfer functions in
multibox E UT
cable # 1
cable # 2
----CABLE
UNDER TEST
R X PROBE
FREQUENCY
SIGNAL
LOOP
TRACKING GENERATOR
SIGNAL SOURCE
CABLE UNDER TEST
TRANSFER FUNCTION
(raw data)
W
Q
:::>
f-
::J
0..
TRACKING
GENERATOR
SIGNAL
PASS BAND OF
SPECTRUM
ANALYSER
Both scan
together
IlJ
~t.===========f=2~
::E
JJL.
SPECTRUM
ANALYSER
«
SIGNAL TRACKS WITH ANALYSER
• to measure probe I probe coupling
O..-------r------.-----r------.-----__,
·10
FUNDAMENTAL LINE SELF RESONANCE
_ ·20
CO
"0
CURRENT TRANSFER
CHARACTERISTIC
as measured in' \ 8.23
W
...J
«
u
w
\
(/)
Cl
::>
:J
I0~
«
RADIATED SIGNAL STRENGTH
1m from the cable
-70
-8001-------1------1-----'-----...1.----"'
80
40
60
20
100
o
FREQUENCY MHz
Figure 8.24
Current transfer characteristic and measured
radiated signal strength from simple test
transmission line
Reproduced by permission or BAe Dynamics Ltd.
Many spectrum analysers, including those with
synthesised local oscillators have builtin tracking
generators and this extends the capability of the
spectrum analyser in carrying out diagnostic
EMC measurements as described.
8.11 RF power all1.plifiers
8.11.1 Introduction
Power amplifiers are required to raise the signal
power ou tpu t from a synthesiser or sweeper signal
source to a level required by the ou tpu t
transducer to perform the EMC test in question.
Thus amplifiers will usually have a stable input
signal from a well defined source impedance but
must drive current probes, capacitive coupling
blocks and a wide variety of antennas which are
often situated in reflective screened rooms. Such
ou tpu t loads will not in general present a good
VSWR to the amplifier output. In fact, EMC
testing is one of the most demanding uses to
which high power broadband RF amplifiers can
be put in terms of output VSWR and final stage
amplifier protection.
The frequency range of EMC susceptibility tests
is large (up to 18 or 40 GHz) and a number of
amplifiers are required to cover this range in up
to ten contiguous bands. As they also need to
provide at least 100 W output power in bands
below 1 G Hz and 10-100 W above this frequency
they tend to be one of the most expensive capital
assets in the test laboratory. I t is therefore
important that EMC test engineers and managers
in companies developing products which must
meet EMC standards, and who plan to invest in
EMC test equipment, should understand the
performance limi ta tions and design compromises
pertinent to RF amplifiers.
One of the most difficult requirements to satisfy is
the production of an amplifier with broadband
coverage and high power in the same package. Part
of the problem lies in the bandwidth limitation of
the power devices themselves where the internal
capacitance is the limiting factor. If this capacitance
is reduced by making smaller semiconductor
devices, their power handling is also reduced. The
RECEIVERS, ANALYSERS AND MEASUREMENT EQUIPMENT
amplifier designer faces limits in device gainbandwidth product and power handling which can
only be minimised by careful circuit design.
Unsophisticated broadband high-gain (1 MHz1 GHz, 30 dB) amplifiers have a tendency to
break into oscillation and much design effort is
directed towards ensuring stable operation, particularly when driving poorly matched loads which
is the norm in EMC testing.
10,000
10 kW ( 10kHz - 100 MHz)
I
Specifying RF amplifiers for a range of EMC tests
is a demanding task and mistakes can lead to
gaps in the testing offered, an unacceptable level
of amplifier malfunction or an increase in test
times, all of which can have an adverse economic
impact on the facility operation. The following
list suggests the performance parameters which
should be addressed when evaluating the
suitability of an amplifier for use in EMC testing.
8.11.2.1 Frequency range
This should be as broad as possible consistent with
cost. The fewer band switches or amplifier changes
the faster the test can be conducted. Typical
practical amplifier frequency ranges are
Solid-state amplifiers (100 W-1 kW)
10Hz -100 kHz
10 kHz -200 MHz
200 MHz-400 MHz
(for power output of > 100 W)
200 MHz-1 G Hz (for ou tpu t powers < 100 W)
TWT amplifiers (10W-100W)
1 GHz - 2GHz
2GHz
4GHz
4GHz - 8GHz
8 GHz -12.4 GHz
12.4 GHz-18 GHz
TWT amplifiers (1 W-I0W)
18 GHz -26.5 GHz
26.5 GHz-40 GHz.
I
2.5 kW ( 10k - 220 MHz)
I
1000
1 kW (220 - 400 MHz)
I
1kW (10 k -220 MHz)
750 W ( 10k - 220 MHz)
750 W ( 400 MHz - 1 GHz)
I
I-
~
250W
(10 kHz220 MHz)
100
I
i
100 W (100 -1000 MHz)
:::>
o
ex:
50
w
~
a.
I
300 W ( 400 MHz - 1 GHz)
200 W ( 220 - 400 MH~ )
I-
8.11.2 Specifying an amplifier
145
(1 -1000 MHZ)
I
10
10 W ( 1 - 1000 MHz)
I
I
5 W ( 500 kHz - 1 GHz)
1
.01
1
100
2CfO
400
FREQU~NCY
Figure~ 8.25
I
600
I
800
1000
MHz
Examples oj RF amplifier power output
and bandwidth. Data Jor examples from
amplifier research
Reproduced by permission of Amplifier Research
with the widest bandwidth and the highest power
possible within the budget constraints.
EMC immunity levels are likely to increase in
the coming years and more RF power will be
req uired to carry out the tests. A factor of three
increase in field strength in a radiated susceptibility specification will req uire a factor 10
increase in power amplifier capability. Amplifier
cost increases very rapidly with output power and
it is therefore preferable to purchase expansion
potential at the start rather than pay for increasingly capable new equipment.
A
chart
of high-performance
amplifier
capability [32J (power against frequency) is given
in Figure 8.25. The trend represented in this
figure is a movement fron1 very broadband at low
power (1 GHz at 5 W) to a smaller bandwidth at
very high power (100 MHz at 10kW).
8.11.2.2 Power output
Typical power output required for 1-3 m EMC
susceptibility testing at up to 10 V jm is 10 to 100 W.
The amplifier manufacturers do not always make it
clear whether they are specifying maximum output
power, mean power (according to some definition)
or minimum output power. Whenever possible,
amplifiers for use in EMC testing should be specified
against minimum power output. This will enSlJre
that the field strengths or induced current levels can
be produced and will give in some cases up to 3 dB
headroom in performance [32]. Experience suggests
that the best purchase strategy is to specify units
8.11.2.3 Amplifier gain
The amplifier gain required will depend on the
ou tpu t level of the signal source being used and
the ou tpu t power calculated as being required to
produce the required field strength or induced
current specified in the tests. Usually the signal
source will have an ou tpu t in the range 0+ 13 dBm and a gain of 40-50 dB will be required
to reach full ou tpu t in excess of 100 W. The
maximum output power of an amplifier will vary
across its frequency range typically by ± 1.5 dB,
and the rated output should be specified at the
146
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
20,000 r----r:':~r:--__,-~--.--.......---r-......-~....-......----.- ......-.--.......-
Figure 8.26 Amplifier output
power exceeds rated power
through frequency band for ~
high quality equipment.
w
( Selection from Amplifier ~
Research products)
~
10,000
_
.........± 1.5dB
_
]± 1.5 dB
5000
2000
___~~
!!,i~::.~
:::J
0....
:::J
250L
o
o
w
200
~ ffi
100
a.
20
a:
10
o~
min gain = 54 dB
_ _ _ _ _ _ _ _ _- - - - - 5 0 L
----- --- --- --- - - ---
LL
5
( 1.5 dB =
lower bound of this range to ensure the specified
output power is always available. See Figure 8.26.
8.11.2.4 Gain compression
An amplifier will respond nonlinearly when the
input signal is sufficient to drive the output near to
saturation, when no more power can be generated.
As the output approaches saturation the amplifier
gain is compressed and starts to fall off as
illustrated in Figure 8.27. Knowing the output
power at which the gain compression is 1 dB for
example, is important if the equipment is to be
used for amplifying signals with superimposed AM.
If AM signals are passed through a nonlinear
amplifier, spurious distortion signals will be
generated. This is not so important if FM or
pulsed signals are being amplified, and amplifiers
are often run at the saturated level for these signals.
GAIN
THEORETICAL
COMPRESSION
LINEAR
I
( 1.0 dB )
OPERATION ~~#
T7-----~-71
"0
0:
W
~
o
r
~
/
OUTPUT POWER
at 1.0 dB gain
compression
~
I
I
I
0I-
ACTUAL
AMPLIFIER
OUTPUT
I
I
::>
0-
I-
::>
o
(G = slope)
Maximum drive level for
linear operation
I
I
-I
I
INPUT POWER dBm
Figure 8.27
Gain and output power behaviour near
amplifier maximum output
Reproduced by permission of' Amplifier Research
5 10 20
50 100 200 500
FREQUENCY MHz
Reproduced by permission of' Amplifier Research
cc
x 1.4) _
Saturated output power, CW
2
~
--..... . . =& 1.5dB
50
8.11.2.5 Harmonic distortion
This is caused by nonlinearities In the amplifier
response and creates spurious
signals at
harmonics of the fund amen tal at the expense of
power in the fundamental signal frequency. The
choice of amplifier design is importan there;
Class A operation results in the greatest linearity
and the lowest distortion figures. Unfortunately
this mode of operation is not suitable for high
power systems owing to energy dissipation.
Typical
worst-case
harmonic
distortion
components
are
15-20 dB down on the
fundamental signal at the rated power output of
a commercial amplifier.
The control ofharmonic distortion is important in
EMC susceptibility testing as it is possible to ascribe
the failure of an EDT to the susceptibility signal at
the fundamental frequency when it may have been
caused by a harmonic signal. In the worst case
where the transfer function of the antenna or probe
is such that it preferentially selects the harmonic at
the expense of the fundamental, a ghost susceptibility can be produced. Where possible, amplifiers
should be operated well below gain compression to
reduce the harmonic distortion to a minimum. This
is a further reason for purchasing amplifiers with a
greater power capability than is strictly necessary
for a particular test.
8.11.2.6 Intermodulation distortion
This effect is generated when two or more signals
are fed into the amplifier and nonlinearities act to
mix the signals together producing sum and
difference frequencies. This effect is not as
significant for EMC testing as harmonic distortion
RECEIVERS, ANALYSERS AND MEASUREMENT EQUIPMENT
because usually only one signal is amplified at a
time and injected into or radiated onto the EUT.
8.11.2.7 Output protection
Traditionally, high-power RF amplifiers have
used directional couplers on the ou tpu t to detect
a poor match with the load. The signal from the
reverse power port of the directional coupler is
used to trip the power supply to the final stages of
the amplifier and thus protect them against
damage caused by the absorption of the reflected
power. This protection feature is necessary but
can cause problems in EMC susceptibility testing
where serious mismatches occur frequently as the
signal is swept through the frequency band and
the amplifier repeatedly trips out, extending the
test time considerably.
Modern
high-power
semiconductor
RF
amplifiers [31 J can be designed conservatively so
that the reflected power from an open or short
circuit can be absorbed in the output stages
without causing damage. This results in the ability
to conduct the EMC susceptibility test in a single
sweep without repeated stops to reset the amplifier.
8.11.2.8 TWT microwave amplifiers
Travelling wave tube amplifiers are currently used
to provide high output powers of 100 W or more
up to around 18 GHz. They are based on a
thermionic valve or tube the general construction
of which [33J is shown in Figure 8.28. Typical
amplifiers have an octave bandwidth and gains in
the region of 35--40 dB. Sometimes TWTs are
noisy amplifiers and are often combined with
solid-state microwave preamplifiers in a single
equipment to improve the system noise figure.
l'he protection of travelling wave tube highpower microwave amplifiers [34J relies on VSWR
r--------------- -----,
I
I
CONTROL
ANODE
I
\
!H~ 1
I~~~~ I:.:
I
I
I
ELECTRON BEAM
FOCUSING MAGNET
I
ATIENUATOR
/
TUBE BODY
/
>;:::==::tl1fJWm~ tmm~~~
CATHODE
a
HELIX
/l
COLLECTOR
I
T6
ELECTRON
BEAM
I
I
J
TRAVELLING
WAVE TUBE
Figure 8.28
High-power microwave travelling wave tube
and power supplies
Reproduced by permission or Macmillan
147
detection, tube element current monitors, and
power supply shut-down techniques. Making
EMC susceptibility measurements at microwave
frequencies with TWT amplifiers is much more
time consuming than at below 1 G Hz using solidstate equipment. The amplifiers only have an
octave bandwidth, the waveguides and antennas
need to be 're-plumbed' with almost every change
of band and the TWT amplifier is designed to
trip ou t in the presence of high levels of reflected
power due to mismatches.
8.11.3 RF amplifiers -
conclusions
'The selection, purchase and use of high-power
broadband amplifiers for use in EMC susceptibility testing calls for careful consideration if the
best outcome is to be obtained within a limited
budget. Only large test houses and aerospace!
military and automotive companies will have a
need to purchase the largest I-10kW amplifiers
for large system evaluation. More modest
am plifiers in the region of 100 W ou tpu tare
sufficien t for testing most military and commercial
electronic equipments and small units. Amplifiers
with outputs of a few watts are extremely useful
in susceptibility development testing of small units
or circuit boards when used in conjunction with
bounded-wave devices such as GTEM cells.
8.12 Signal modulators
8.12.1 Modulation requirements
The requirements for the modulation characteristics of EMC susceptibility test signals vary widely
with the specification. Often a minimum set of
conditions is laid down with the proviso that
other modulation types, levels and frequencies
should be added if the EUT is designed to
operate in an environment that contains these
specific signals. For example, an equipment that
is to be sited near a radar transmi tter may have
to pass a susceptibility test with the specific
modulation
characteristics
of that
radar.
Generally, the specification of modulation signals
is more detailed for tests on military equipment
than for those on commercial electronics.
A typical set of modulation rules for tests on
military equipment is given in MIL STD 462
(N3, p117) and is listed in Appendix 2 Table
A2.1. A more comprehensive list of modulation
rules for susceptibility tests on military equipment
is to be found in DEF STAN 59-41 (part 3 page
12); and is given in Appendix 2 Table A2.2.
8.12.2 Built-in modulators
From inspection of these tables it can be seen that
the modulation types required for EMC tests fall
148
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
into four basic types: CW, AM, FM and pulse. It
is possible that other more sophisticated types of
modulation such as phase modulation, may occasionally be required, but in most cases modulation
sources which can deliver the four basic types are
adequate for EMC testing. Modern s)'nthesised
signal sources usually have built-in modulators
with a reasonable capability for AM, FM and
pulse operation. Typical performance figures are
given in Table 8.3.
Table 8.3
AM FM
Pulse -
~ypical
built-in modulator performance
Modulation frequency to 50 or 100 kHz
Modulation depth to 99 or 100 %
Modulation rate typically 50 or 100 kHz
but up to 10 MHz
Deviation typically 100 kHz-20 MHz
Risetime from 5-400 ns
PRF typically 0.1-1 MHz
but up to 10 MHz
Not all synthesised signal sources will have the full
range of modulators and care must be exercised in
matching the performance of the modulator with
the modulation requirements for the range of tests
which must be performed. A reasonable costconscious compromise is to use internal modulators
for AM and FM and slow (> 0.5 f.1s) jlow repetition
rate « 1 MHz) pulse modulation, together with
an external fast pulse modulator [35 J.
External fast « 100 ns) pulse modulators may
be based on PIN diodes and are usually only
needed for simulating radar modulation at
microwave frequencies. The requirement is likely
to be specified in the test plan or contractual documentation in addition to the more general range of
modulation parameters set out in the relevant
EMC standards.
A wide range of pulse generators is available
from a number of electronics instrument manufacturers which are suitable signal sources to drive
modulators. Most have 5 V rrTL compatible
50 ohm outputs [36J, and some are capable of
higher ou tpu t voltages [3 7J .
8.12.3 Arbitrary waveform generators
A synthesised signal generator or sweeper with a
suitably capable internal modulator section will
require an input from a mod ula tion signal source.
This can be a simple analogue function generator
[38J or a sophisticated synthesised function [39J or
arbitrary waveform generator [40]. Typical
function generators will produce sine, square,
triangle, trapezoidal AM and pulsed waveforms
with a variable modulation depth at frequencies up
to about 20 MHz. They may also include FM and
sweep-frequency capability. An arbitrary function
generator can produce any programmed waveform
required with frequencies up to about 300 MHz.
Some arbitrary waveform generators can take
direct digital information from a transient digitiser
used to record a signal and then reproduce the
exact waveform which has been captured.
LeCroy [41 J produced a useful tu torial reference
concerning arbitrary waveform or arbitrary
function generators.
The ability to synthesise any type of complex
waveform
is
invaluable
in
conducting
development research into RF system susceptibility. Measured real-world interference currents
on system cables can be reproduced accurately at
a range of increasing power levels to determine the
susceptibility threshold for the system. Arbitrary
function generators are also extremely useful in
prod ucing specific waveforms, such as those for
NEMP or ESD tests, as the complex waveform
characteristics can usually be programmed from
simple mathematical functions and can be
changed at will. This obviates the need for a range
of waveform specific signal generators and
although arbitrary waveform generators are
expensive, they may prove to be a cost-effective
choice for a modulation signal source.
8.13 Directional couplers, circulators
and isolators
8.13.1 Amplifier protection devices
High-power EMC susceptibility testing calls for
the use of high-power amplifiers covering an
extended frequency range including microwave
bands. The widely varying load VSWR forces the
need for protective devices to be installed on the
amplifier output. Directional couplers, power
circula tors and waveguide isola tors are all used in
this application. The choice of which device to
use will depend on the specific amplifier output
circuit, the load and whether the output line is
waveguide or coaxial cable.
8.13.2 Directional couplers
A directional coupler is an RF transmission line
device which bleeds off a known portion of power
flowing in the forward or reverse direction in the
waveguide or coaxial cable. This power can be
measured and the value of the main power flow
can be calculated. The device can therefore be
used to sample the forward power flow, to
measure the reverse power and perhaps use it to
shut down an amplifier which is driving a bad
mismatch. With appropriate detectors and meters
the reflection coefficient or VSWR can be continuously displayed.
RECEIVERS, ANALYSERS AND MEASUREMENT EQUIPMENT
FORWARD POWER
MEASUREMENT PORT
8.13.2.1 Waveguide couplers
Consider the two parallel waveguides shown in
Figure 8.29. Liao [42J gives an explanation of the
functioning of this type of directional coupler. If a
small hole is made between the two waveguides, a
fraction of the power flowing in the primary guide
will propagate into the secondary guide through
the slot antenna and then flow outwards in both
directions. If two identical holes are made Ag /4
apart, or more strictly at a distance
L
8.7
apart where n is any positive integer and Ag is the
wavelength in the guide, the forward power
flowing from port 1 through the two holes and in
the direction of port 4, will add and produce an
output. The backward waves in the secondary
guide propagating toward port 3 are out of phase
with each other and cancel to produce no output
at that port. Thus the coupler acts in a
directional manner.
L=(2n+1>\
I.
4"
POWER IN .
\..
Primary waveguide.
PO~ i
- - ----""' - I
--1Iloo--'- -
.1
-"' -
I
POWER OUT
/
-
-
-
-
_1 PORT 2
I
------Ii'
Irl
;
=~-= ~-.: ~ =---=:= =added PORT 4
Figure 8.29
-----------C
1
2
3
D--....
-
POWER
INPUT
w
C>
--- -- -- --A
B ----lIoo-
---~-----~--
~'A. 9 / 4-1-'A. 9 /4-1
\
POWER OUTPUT
PRIMARY WAVEGUIDE
0.8---~---...-----------.
«
~
o
>
~!:(
~~
5!z
u.. w
f2 ~
wo::
C>::>
«(J)
0.4
~~
>:iE
~t;c
0::
w
>
w
0::
1.5
1.0
ACTUAL FREQUENCY
DESIGN FREQUENCY
}-'igure 8.30
Improvement in useful bandwidth with
three-hole waveguide coupler
( a) Two-hole coupler
( b) Three-hole coupler
Reproduced by permission or HMSO
PORT 3 cancelled=:=' =.(
Secondary waveguide
149
i
Output used to measure
forward power in
primary waveguide
Operation of simple two-hole waveguide
directional coupler. Ag == Wavelength in the
waveguide
The useful bandwidth of the coupler is clearly
limited by the fixed hole separation and phase
cancellation which can be achieved. The
bandwidth can be increased by moving to a
three-hole coupler as shown in Figure 8.30 where
the amplitude of the leakage wave through the
middle hole 2 is twice that of the other two holes
1 and 3 [43]. The reverse voltage divided by the
forward voltage in the secondary guide is a
measure of the useful performance of the
directional coupler. I t is plotted against frequency
divided by design frequency in Figure 8.30 and
the increase in useful bandwidth of the three-hole
coupIer can be seen in Figure 8. 30b.
There are two main criteria which define the
performance of a directional coupler:
Coupling factor: With matched loads on ports 2 and
3 in Figure 8.29 the coupling factor is defined as
8.8
Typical values for coupling factor given by Dunlop
and Smith [44J are -3, -10, -12 and -20dB.
Directivity: The existence of the coupling holes
themselves will produce reflections in both the
primary and secondary guides and there will not
be total isolation between ports 3 and 4. The
directivity is a measure of the ratio of power at
these ports for a matched load at port 2:
directivity
==
1010g (P4/ P3)
8.9
For a good coupler design this val ue is in the region
of30 to 40 dB. Most waveguide couplers are limited
to octave bands and a commercial example of a
high performance coupler is the HP 752A series
[45]. It is possible to put two waveguide couplers
together as shown in Figure 8.31 and install diode
Diode detector produces DC voltage
proportional to reverse power
"C
~
MATCHED LOAD
4
FORWARD
POWER-TO-LOAD
Vr
_ _ _~I
~
I
:~:::;-~I_~B
~
./'1~ --1
'A.g
"4
MATCHED
LOAD
Figure 8.31
Vf
REFLECTED
POWER
FROM LOAD
0
Diode detector produces DC voltage
proportional to forward power
Dual directional coupler
Reproduced by permission or HMSO
150
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
detectors in the forward- and reverse-coupled ports
to enable the forward and reverse power to be
deduced from the voltages Vi and Vr • Then the
reflection coefficient p is
DC signal is proportional
to reflected power
DIODE DETECTOR
8.10
and
VSWR == 1 + P
8.11
1-p
8.13.2.2 Coaxial couplers
The need for ease of connection and maximum
bandwidth in transmission lines and components
for use in susceptibility testing, drives the EMC
engineer to the widespread use of high-grade lowloss coaxial cable where possible. Thus directional
couplers based on coaxial rather than waveguide
designs are useful.
Kraus [46] gives an explanation of the
functioning of a coaxial directional coupler which
uses small lengths of wire parallel to the centre
conductor within the coaxial system and
terminated at opposite ends by a resistance equal
to the characteristic impedance of the wire. The
other ends of .the wires are brought through the
outer sleeve as shown in Figure 8.32 to form the
forward and reverse voltage ports. A commercial
example of a broadband 2-18 GHz directional
coupIer with precision type N coaxial connectors
is the HP 7725 [47] which has a coupling factor
of 20 dB and a directivity of around 30 dB with a
power handling capacity of 50 W. Such a coupler
is ideal for use with broadband network analysers
or as a component in levelling broadband power
amplifiers for EMC susceptibility measurements
as shown in Figure 8.33.
Forward power to hom is measured and
fed back to signal source as a levelling loop.
Figure 8.33
Dual directional coupler used to level
forward power and provide reflected power
amplifier shut down signal when conducting
radiated susceptibility test
SHUNT COAXIAL HYBRID RING
I2Zc
1------11
E - PLANE WAVEGUIDE HYBRID RING
3A.g
4
3
t 1
E
OUTPUT FOR WAVE TO THE LEFT
( REFLECTED POWER)
INNER
CONDUCTOR
3
---~-
OUTPUT
CONNECTOR
fo
LOAD
Za = impedance of waveguide
=wavelength in wavegu ide
Ag
AUXILIARY
CONDUCTORS
\
OUTPUT
CONNECTOR
Figure 8.34
Coaxial and waveguide hybrid rings
Reproduced by permision of Prentice Hall Computer Publishing
AUXILIARY
CONDUCTORS
Figure 8.32
OUTPUT FOR WAVE TO THE RIGHT
( FORWARD POWER)
Coaxial directional coupler
Reproduced by permission of McGraw-Hill
8.13.3 Hybrid rings, circulators and
isolators
8.13.3.1 Hybrid ring
A four-port hybrid ring can be constructed In
ei ther waveguide or coaxial transmission lines as
in Figure 8.34. I t has the property that there is no
direct coupling between arms 1 and 4 or between
2 and 3 [48]. Power flows from port 1 to port 4
only by virtue of reflections generated by
mismatches at ports 2 and 3. This device can be
used as automatic amplifier output protection as a
high-power load can be placed at port 4 and the
amplifier power entering port 1 will be automatically diverted safely to this load should a
mismatch occur at the normal load port.
RECEIVERS, ANALYSERS AND MEASUREMENT EQUIPMENT
8.13.3.2 Circulator
A circulator is a nonreciprocal transmission device
that uses the property of Faraday rotation of the
wavefield in a ferrite material [42]. I t is a
multiport waveguide junction in which the power
can flow only from the nth port to (n + 1) th port
in one direction, see Figure 8.35. The design uses
a combination of side-hole directional couplers
and nonreciprocal phase ferrite shifters. This
device can also be used to protect the ou tpu t of
expensive microwave amplifiers when conducting
EMC radiated susceptibility tests.
PORT 4
PORT 3
PORT 1
PORT 2
Figure 8.35
Four-port circulator
microwave amplifier tubes from dalnaging the
input signal generator. The isolation is gained
however at a price, namely the slight forward
power insertion loss, which might typically be up
to 1 dB at frequencies below 26 GHz. Isolators
are a useful component in constructing robust
high-power microwave susceptibility test systems
which can withstand the daily 'abuse' from
mismatches caused by wavefield reflections inside
shielded rooms, and the occasional cable fa ul t or
broken waveguide flange.
8.13.4 Protection devices -
Waveguide isolators also use Faraday rotation
and incorporate a 45° waveguide twist to isolate
the forward and reverse power in the guide [41].
Dunlop and Smith [44] explain the principle of
operation and the usual waveguide configuration
is shown in Figure 8.36. The resistive vane is
oriented in the plane of the reflected wave E-field
acting as the built-in reflected power load. These
isolators are often used to prevent the reverse
power flow from the inputs of high-power
REFLECTED
POWER
0
45 rotated
clockwise
E fields of reversed
power absorbed in
resistive vane
All the devices described above can be used to
protect the expensive investment of high power
broadband amplifiers and signal sources which
are used in EMC testing. They are inexpensive by
comparison, and their specification should be
considered carefully together with the amplifiers
and antennas which make up the test system. A
working knowledge of their function and capabilities is essential for the EMC engineer who is
entrusted with carrying out susceptibility testing
while protecting the amplifiers and keeping the
repair time for this equipment to an absolute
mInImum.
8.14.1 Introduction
When the number of tests being performed in a
facility to a single or restricted range of specifications increases, EM C engineers consider the
optio.n of automating the process. A company
whose products are all tested to EN 55022 might
find it economically worthwhile investing in the
microprocessor- based measuremen t eq uipmen t
and desktop or minicomputer controllers
required. They could then purchase or write the
software needed to carry ou t these particular tests
and ensure tha t all tests were carried ou t
identically. In addition, automation of EMC
testing has a number of potential advantages.
•
•
,.>
"'I
h:,. -,.
l'
IN
~ 45
E,."- ~
1~
Figure 8.36
0
rotated
clockwise
~ 450 rotated
•
anti-clockwise
E-field rotation in waveguide isolator
Reproduced by permission
conclusion
8.14 Automatic EMC testing
8.13.3.3 Isolators
POWER
151
or Van Nostrand
Reinhold
I t increases the work through pu t by speeding
up measurement.
I t can be used to deskill the testing job,
although this is probably a shortsighted
economy because EMC testing is best
undertaken by staff who will be alert to
unusual phenomena and be capable of their
correct interpretation.
It allows reports to be produced quickly and
cheaply to a standard format.
In most automated EMC test facilities the testing
cost can be kept low and the job satisfaction for the
152
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
test engineer improved as the equipment takes care
of the routine aspects of measurement, leaving the
engineer free to concentrate on quality issues and
experimental or diagnostic procedures which need
the flexibility of the human mind.
8.14.2 Automated emission testing
Fully automatic, blind EMC testing is not
possible, nor perhaps desirable. Compu ter assisted
or semiautomatic testing which cuts down test
time and drudgery, most certainly is. The
development of suitable software that can cope
with all the decisions that need to be made during
an emission test is not trivial. Consideration must
be given to
Frequency stepping increment
Scan speed and the assembly of multiple scans
to fully cover the bandwidth of a pulsed signal
spectrum
Selection of bandwidth according to test specification, measurement frequency, or signal
conditions
Alteration of detector function and classification of signal types
Real-time manipulation of input and IF
attenuation depending on signal level
Determination or recognition of background
ambient signals and appropriate marking
(when making open-range measurements)
Swi tching antennas or sensors with frequency,
or location on or around an EUT
Adjusting the height of an antenna to find
maximum signal strength from an EDT on an
open site
Driving the turntable in steps during an opensite test
Periodic calibration routines
Data storage and manipulation
Storage and retrieval of dozens of sensor
transfer functions
Storage, retrieval and comparison of specification limits with measured levels
Calculation of out of limits signals, data
presentation and storage
Plotting rou tines and prin ting of test instrumen t
parameters to meet QA requirements
Filing of archive material in the form of
removable discs, tapes or cassettes.
Many of these factors are considered in a paper by
Sikora [49J dealing with the production of EMC
test automation algorithms and methods of
performing computer controlled EMI compliance
tests are examined by Derewiany et at. [50J. A
brief description of some hazards to be avoided
with automated EMI testing IS given by
Archambeault [4J.
Most manufacturers of EMI receivers and
spectrum analysers for use in E~1C emission
testing supply computer assisted test suites with
software tailored to military and commercial
equipment test standards. The verification and
documentation of these software packages are
most important as they form part of the traceable
quality chain which underpins statements of
measurement accuracy and repea tability.
8.14.3 Automated susceptibility testing
I t is more difficult to automate radiated and
conducted susceptibility testing because the
control computer must be able to monitor the
performance of the EDT directly, to stop
frequency scans and carry out investigative
procedures at susceptible points. In addition, the
number of connections between signal sources,
modulation sources, power amplifiers and
antennas or injection probes mean that the testing
will inevitably be time consuming.
While compu ters can be useful in setting up test
configurations and in controlling some signal
sources and feedback levelling loops, susceptibility
testing is labour intensive as it is of a primarily
investigative nature.
8.14.4 In the future?
There can be no doubt that computer technology
will become increasingly powerful, cheap and
available. Software will also improve and exciting
prospects lie ahead in the field of EMC design,
modelling and testing. The bringing together of
large complex design models and responsive EMC
test algorithms within the framework of a
knowledge-based architecture may result in much
more careful and discriminating tests being
carried out on particular types of equipment, or
the execution of specific tests designed to reveal
the true EMI characteristics of individual items
being tested.
8.15 References
CONNEY,
M.
and
ERICKSON,
S.A.:
'Considerations in the design of a multi-bandwidth,
sensitive, wide dynamic range, wide frequency
range EMI receiver'. Proceedings of IEEE
symposium on EMC, 1990, pp. 634-637
2 EMI meter NM17-27 instruction manual. Carnel
Labs. Corp, 21434 Osborne Street, Canoga Park.
CA 91304, USA, p. 5.15
3 WHITE, DJ.: 'A handbook series on electromagnetic
interference and compatibility, volume 2 test and
measurement procedures'. Don White Consultants,
Germantown, Maryland, USA, pp. 3.66-3.86
RECEIVERS, ANALYSERS AND MEASUREMENT EQUIPMENT
4 ARCHAMBEAULT, B.R.: 'Hazards to avoid with
automated EMI testing'. Interference technology
engineer's master 1985, pp. 118-122
5 DUFF, W.G.: 'Fundamentals of electromagnetic
compatibility'. Interference Control Technologies
Inc, Gainsville, Virginia, USA, pp. 319-320
6 'TD2301/TD1301 High performan~e digitizer
systems with Fourier analysis capability'. Tektronix
catalogue, 1990, pp. 162-163
7 STURLEY,
K.R.:
'Radio receIver design'.
(Chapman & Hall, London, 1949)
8 LANGFORD-SMITH,
F.:
'Radio
designers
handbook' (Iliffe Books, London, UK)
9 'AN 246-1/5952-8815 Optimising the dynamic
range of the HP 3585A spectrum analyser'. HP,
Winnersh, Wokingham, Berks, UK
10 'AN 150/5952-1213 Spectrum analyser basics'. HP,
Winnersh, Wokingham, Berks, UK
11 'AN 150-1/5954-9130 Spectrum analysis AM and
FM'. HP, Winnersh, Wokingham, Berks, UK
12 'Signal strength & interference measurements'.
News special 1, Rohde & Schwarz, Ancells Business
Park, Fleet, Hampshire, GU13 8UZ, UK
13 CISPR EMI receIvers 8573A/8574A. HewlettPackard 1990 product catalogue, p. 125
14 85685A preselector, Hewlett-Packard 1990 product
catalogue, p. 126
15 BELDING, R.L.: 'RF preselection requirements for
spectrum
analysers'.
Proceedings
of IEEE
symposium on EMC, 1985, pp. 94-97
16 Microwave EMI receiver EMC-60/FE-60. ElectroMetrics Ltd, I vel Rd, Shefford, Beds, SG 17 5JU,
UK
17 Band rejection filters TRF11-TRF15. Electro-Metrics
Ltd, Ivel Road, Shefford, Beds, SG17 5JU, UK
18 'High and low-pass RFI filters, instruments,
components and accessones for the RFI/EMC
engineer'. Data sheet 6625A, Solar Electronics Co,
901 North Highland Ave., Hollywood, CA 90038,
USA
19 KEISER, B.: 'Principles of electromagnetic compatibility' (Artech House, Norwood, MA, 3rd edn.)
p. 347
20 Carnel Labs. Corporation (formally Eaton) 91263-1
stand-alone 1 GHz impulse generator
21 EMI meter NM17-27 with built-in impulse
generator instruction manual. Carnel Labs. Corp,
21434 Osborne Street, Canoga Park, CA 91304,
USA, p. 2.1
22 SP-P-90203 Product-specific EMC standard for the
Tornado military aircraft, Panavia, Europe
23 Disturbance analyser Series 606, Dranetz company,
USA
24 Digitising oscilloscopes HP 54120 series, Hewlett
Packard 1990 test and measurement catalogue. HP,
VVinnersh, Wokingham, Berks, RG11 5AR, UK, p. 60
25 'Fundamentals of digital oscilloscopes and waveform
digitising, A technical tutorial'. 1990 product
catalogue, section IV-I. LeCroy, 700 Chestnut
Ridge Road, Chestnut Ridge, NY 10977-6499, USA
26 1990/1 measurement equipment catalogue. Rohde
and Schwarz UK Ltd, Ancells Business Park, Fleet,
Hampshire GU13 8BR, UK, pp. 384-387
27 'Power sensors' in Test and measurement catalogue
28
29
30
31
32
33
34
35
36
37
38
39
40
4J
42
43
44
45
46
47
48
49
50
153
1990.
HP
Winnersh,
Wokingham,
Berks,
RG 11 5AR, UK, p. 204
1990/1 measurement equipment catalogue. Rohde
and Schwarz UK Ltd, Ancells Business Park, Fleet,
Hampshire GU13 8BR, UK, p. 428
Directional power meter RFM 100 in Rohde and
Schwarz measuring equipment catalogue 1990/91,
p.429
WHITE, DJ.: 'A handbook series on electromagnetic
interference and compatibility, Volume 2 test and
measurement procedures'. Don White Consultants,
Germanton, Maryland, USA, p. 3.92-3.103
PITT, A.D.: EMC guidelines, ST23357. British
Aerospace Dynamics Ltd, Filton, Bristol, UK, 1979
'Guide to broadband power amplifiers'. Amplifier
Research, Rev. 0190, 160 School Hse Rd,
Souderton, PA 18964-9990, USA
SCHEVCHIK, V.N.: 'Fundamentals of microwave
electronics'. (Macmillan, NY, USA, 1963) pp. 186-203
TWT amplifiers. Keltec Florida Ltd, PO Box 862,
Shalimar, FL 32579, USA
Fast pulse modulator, HPl1720A. HP 1990
catalogue, p. 392
Pulse generator, PM 5771, 1 Hz-100 MHz. Philips
Instruments UK
Pulse generator PG 73N, 0.ls-10ns. Lyons
Instruments, Hoddesdon, Herts, UK
Analogue function generator HP 3212A. HP 1990
catalogue. p. 428
Function generator AFG. Rohde and Schwarz
measuring equipment catalogue 1990/91, p. 90
Arbitrary function generator 9100, 1990 product
catalogue. LeCroy, 700 Chestnut Ridge Road,
Chestnut Ridge, NY 10977-6499, USA
'The hows and whys of arbitrary function
generators, A technical tutorial'. 1990 product
catalogue, section IV-48, LeCroy, 700 Chestnut
Ridge Road, Chestnut Ridge, NY 10977-6499, USA
LIAO, S.Y.: 'Microwave devices and circuits'.
(Prentice Hall, Englewood Cliffs, NJ, USA)
pp. 158-169
GLAZIER, E.V.D. and LAMONT, H.R.L.: 'The
services textbook of radio, volume 5, transmission
and propagation'. (HMSO, London, UK, 1958)
p. 225
DUNLOP, J. and SMITH, D.G.: 'Telecommunications
engineering'.
(Van
Nostrand
Reinhold, UK) p. 288
'Waveguide directional couplers HP752 series. HP
1990 catalogue, p. 345
KRAUS, J.D.: 'Electromagnetics'. (McGraw-Hill,
3rd edn.) p. 420
'Coaxial directional coupler' HP 772D, HP 1990
catalogue, p. 344
'Hybrid ring, reference data for radio engineers' in 'ITT
handbook' (Howard W. Sams) pp. 25/18 and 25/19
SIKORA, P.A.: 'Writing a useful EMI test
automation algorithm'. Proceedings of IEEE
symposium on EMC, 1988, pp. 377-382
DEREWIANY, C.F. and KOWALCZYK, K.R.:
'Methods of performing computer controlled EMI
compliance tests'. Submarine electromagnetic
systems dept. Naval Underwater Systems Center,
New London, CT 06320, USA
Chapter 9
EMC test regitrles and facilities
9.1 Introduction
possible to cover all these interesting topics, but
information is widely available in the proceedings
of relevant specialist groups sponsored by the lEE,
IEEE and others. This chapter concentrates on the
testing regimes and test facilities most generally in
use for electromagnetic compatibility testing.
9.1.1 Main test regimes
This chapter examines the three principal test
regimes and facilities in which these devices and
equipments are used to conduct EMC tests:
testing in screened chambers, open-range testing,
and 'low-level swept' and bulk current injection
testing. The majority of standard EMC test work
carried ou t on commercial and military electronic
equipment falls into one of these three regimes.
9.2 EMC testing in screened
cham.bers
9.2.1 Enclosed test chambers
In conducting EMC tests to measure both
equipment RF emissions and susceptibilities, it is
desirable to isolate the test space from the outside
electromagnetic environment. If arbitrarily varying
ambient RF signals (up to field strengths of 10 V /m
in industrial areas) are allowed to mix with the
signals of interest ofa mV/m or less from the EUT,
it will be time consuming and almost impossible to
separate out the signals which need to be measured
to the levels required by the specifications.
Equally, it is undesirable (and illegal) to radiate
high field strengths across whole bands of
frequencies when conducting radiated susceptibility
testing. rrhus the use of screened chambers became
widespread as a result of military procurement
EMC requirements which came to the fore during
the late 1960s and early 1970s. Much of the custom
and practice with regard to the use of screened
chambers has been built up on the basis of
standards imposed on the aerospace/military
equipment industries such as MIL STD 461/2/3.
Many of the tests currently being carried out are
either the same, or directly related to those in early
specifications such as this. Of course, increased
knowledge and test experience gathered over 20
years have been incorporated into modifications to
test methods, or to new tests such as those relating
to BCI (bulk current injection) contained in the
UK DEF STAN 59-41 DCS02.
The advent of widespread governmental or self
regulation of EMI in the early 1980s connected
with commercial electronic products such as digital
computers, brought about the widespread use of
EMC tests based in some cases on earlier CISPR
type methods. These new tests were largely
concerned with the control of radiated and
conducted emissions (FCC part 15, VCCI, etc) and
made use of open sites rather than screened rooms
as suggested for testing military equipment.
9.1.2 Special testing
There are of course other specialised types of electromagnetic testing which are either related to the
type of electromagnetic threat employed or
signature being measured, or to the scale of the
testing on large systems. The special testing
techniques related to threat or signature type are
•
•
•
Special electromagnetic threats
HIRF (high intensity RF) tests
Ligh tning strike tests
NEMP (nuclear electromagnetic pulse)
testing
EMP (electromagnetic pulse) and HPM
(high power microwave) testing
Special signature testing
Tempest (emission security) tests
Spacecraft EM 'cleanliness' (from DC
magnetic fields to millimetric waves)
Special test techniques related to the scale of a
test include
whole-ship testing
whole-aircraft clearance
telephone switching centres
large distributed computer facilities
large communication centres
transportation signalling centres.
In some cases, it is possible that these large systems
need to be tested for EMC, NEMP/EMP,
lightning and Tempest.
The range of testing requiren1ents that facilities
must sometimes meet leads to increasing facility
cost, and the procurement or licensing authorities
may not impose the full range of specifications for
all these electromagnetic effects on a given system
unless absolutely necessary. In a book such as this
devoted to generalised EMC testing it is not
154
EMC TEST REGIMES AND FACILITIES
There are therefore almost two parallel streams
of EMC testing with each general approach
having its own advantages and penalties optimised
for the type and cost of testing which needs to be
carried out in the civil and military fields. I twill
be interesting to see if the sharing of testing
information between these two communities leads
to a consensus oh the best and most cost-effective
test methods for particular types of equipment.
The practice of testing in screened rooms has
then largely been established by the need to test
equipment to military specifications where the
EUT performance is critical, the unit cost is high
and the project budgets are large. In these circumstances it is possible to build elaborate high cost
(> £5 M) test facilities on the basis of large,
sometimes very large (1 OOx 80 x 20m), shielded
enclosures in which to carry out the work. White
[1] gives examples of large facilities constructed
for ballistic missile and aircraft testing. The only
other product areas which have invested in such
large facilities are the automotive and space
industries and to a lesser degree the civil aircraft
sector.
Screened test chambers used for EMC testing
can be divided into four types: standard shielded
chambers, shielded and anechoic chambers,
mode-stirred chambers, and novel facilities.
Screened chambers made from metal sheets are
usually constructed in the form of a rectangular
box with parallel sides, but other configurations
such as cylinders and tapers have been built for
special req uiremen ts of items to be tested or to
minimise reflectivity. Screened chan1bers are an
expensive item of equipment and costs typically
range from £20,000 for an 8 x 6 x 4 m room to
more than £20 M for one in which a large system
could be tested.
9.2.2 Standard shielded enclosures
Standard screened rooms are mostly constructed
from thin galvanised sheet steel and wood
sandwich modular panels that are clamped
together with special pressed metal strips to
produce an RF-tight joint. This permits the
building of structures of variable size which can
be dismantled and re-sited if required. Other
types of construction include self supporting allwelded sheet steel, copper sheet, metal foil, and
'chicken wire', perforated sheet or expanded steel
mesh. Each construction technique provides a
certain degree of shielding for a given enclosed
volume at a particular cost. Careful analysis of
the shielding requirement to carry out a given
EMC test must be undertaken if the correct
performance of room is to be achieved for the
minimum cost.
155
Farsi [2] gives a good introduction to shielding
theory and shows that for plane waves the
shielding effectiveness is
S
==
R
+A +B
(all in dB)
where R == reflection loss
A == absorption loss
B == internal loss
The internal loss factor B is usually neglected if the
absorption loss is significan t [2]. The reflection loss
IS
R
where
==
168
+ 10logb/fll (dB)
9.1
f == frequency
in MHz
b == material conductivity
Il == material permeability
The reflection loss for a plane wave is a function of
the material conductivity and is high at low
frequencies and reduces at higher frequencies.
Expressions for the reflection losses of the electric
and magnetic field components of a wave are
given in Reference 2 which allow the loss to be
calculated for nonplane waves such as occur in
the near field of a source.
The absorption loss is dependent on the type of
rna terial and its thickness and is
A
==
3.34tjfbll (dB)
9.2
where t == material thickness in mils (,thou')
f == frequency in MHz
b == material conductivity
Il == material permeability
White [3J, quoted by Farsi [2J, gives a table for
the absorption loss per thousandth of an inch
thickness for materials commonly used to
construct shielded rooms, see Table 9.1.
The configuration of a typical small screened
room complex used for EMC testing is shown in
Figure 9.1. I t has the EMI receivers, power
amplifier 'transmitters' and the EUT shielded each
from the other, and all from the outside
environment. I t is possible to have a shielded room
only for the EUT in a single cell facility, but the
isolation scheme shown in Figure 9.1 is useful for
multicell operation in a large test facility complex
where emission and susceptibility testing on
different EUTs may be running simultaneously.
The practical performance of screened rooms is
unlikely to be determined by the plane wave
propagation through the shield material but
rather by leakage through panel seams, corner
joints, penetration panels and access door
surrounds. Typical shielding effectiveness of a
moderate sized modular room of 12 x 7 x 5 m
with large 4 x 4 m doors, air vents and multiple
penetration panels is shown in Figure 9.2.
156
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
Table 9.1
Electromagnetic characteristics of metals and absorption loss with thickness
Metal
Silver
Copper
Gold
Aluminium
Zinc
Brass
Nickel
Bronze
Tin
Iron
Steel (SAE 1045)
Stainless steel
Absorption loss, dB per 0.001 in
1 MHz
10 kHz
100 Hz
Relative
conductivity
Relative
permeability
100 kHz
0.34
0.03
0.28
0.26
0.17
0.17
0.15
0.14
0.13
4.36
3.32
1.47
1.05
1.00
0.70
0.61
0.29
0.26
0.20
0.18
0.15
0.17
0.10
0.02
1
1
1
1
1
1
1
1
1
1000
1000
1000
0.03
0.03
0.03
0.03
0.02
0.02
0.01
0.01
0.01
0.44
0.33
0.15
EMI RECEIVER SHIELDED ROOM
EUT POWER
LINE FILTERS
\
POWER
AMPS &
SIGNAL
____ SOURCES
I
I
I
I
L:N:AJ__--\.\---.. .l
AIR VENTS
Figure 9.1
~POWER
\
POWER
LINE
FILTERS
AMPLIFIER
SHIELDED
ROOM
TEST AREA SHIELDED ROOM
Compact multiscreened room EMC test cell
3.40
3.00
2.78
2.60
1.70
1.70
1.49
1.42
1.29
43.6
33.2
14.7
together. Figure 9.3 shows the attenuation
afforded by a 6 mm-thick mild steel all-welded
construction with two moderate sized doors (2.5
and 3.5 m sq.) and the usual complement of air
ven ts and penetration panels [4 J.
The shielding performance of screened rooms to
be used for EMC testing is almost always measured
according to the method specified in MIL STD 285
[5]. The original standard was introduced in June
1956 and is still largely unchanged. Cardenas [6J
has conducted experiments to define the most
practical measurement methods based on MIL
STD 285, which requires attenuation measurements to be made using a range of identical
antenna sets similar to those shown in Figure 9.4.
140
Improved low-frequency shielding can be
obtained by constructing a chamber from large
heavy gauge steel plates which are all welded
100
co
"'0
z
o
~
120
co
120
"C
Z
0
80
zw
60
~ 100
~
::J
~~
80
~.
c
60
~
40 i--_"""--_..J-_--'-_.....&_----I......._""'-_~ _
w
o
oa:
w
Z
w
o
«
Figure 9.2
40
-
6 mm welded steel plate
- typical modular
screened room
20
___'
1kHz 10kHz 100kHz 1MHz 10MHz 100MHz 1GHz 100Hz 1000Hz
00
-
0
1
FREQUENCY
Typical attenuation oj modular steel-screened
room. Dimensions: 12 X 7 X 5 m;
Access: Doors 4 X 4 m and 1 x 2 m,'
Attenuation: measured at apertures
(doors, attenuvents, etc.)
Reprod uced by permission of BAe Dynamics
Figure 9.3
10
100
1k
10k 100k 1M 10M 100M 10
FREQUENCY Hz
100
Good low-Jrequency performance oj welded
steel room. Welded room type: cylindrical
14m dia X 12m high. - - 6rnm welded
steel plate; - - - typical modular screened
room
Reprod uced by permission of BAe Dynamics
EMC TEST REGIMES AND FACILITIES
157
Shielded enclosure
Shielded enclosure
72" where practicable
(b)
(a)
Electro-metrics ,
RVR -25M
Shielded enclosure
Shielded enclosure
I
I
i!
min. 2"
Receiver
I
Figure 9.4
100
co
"0
Z 80
0
i=
«
60
:::>
Planewave
specification
Electric Field
sPecification
z
~
40
20
0.001 0.01
0.1
1.0
10.0
100 1,000 10,000
FREQUENCY MHz
Figure 9.5
72" where practicable
~ ~
·s..
1 ( 1 .
~A.
12-8-2
li-~
( d)
(c)
Typical equipment corifigurations Jor measurement oj screened room attenuation. (a) LF magnetic Jield test
equipment, (b) Planewave « 1 GHz) test equipment ( c) Electric Jield test equipment (d) Planewave
(10 GH;~) test equipment
Strictly, the MIL STD 285 requires the Tx antenna
to be outside the room in all cases to minimise the
swamping effect of ambients, but at VHF and
above, any signal which has leaked into the room
sets up standing waves which makes it difficult to
locate the source of a leak. At these frequencies the
Rx antennas have some discrimination against
ambients and thus it may be better to put the
receive antenna outside the shield [6J.
The National Security Agency in the USA
issued a specification NSA65-6 for the performance of screened chambers constructed from
metal foil which is shown in Figure 9.5. Although
the cheaper foil-shielded rooms covered by this
specification were not intended for EMC testing
they are in fact quite adeq ua te for this purpose
with attenuation of 100 dB from 1 MHz to 10 GHz.
Well-constructed shielded rooms are very efficient
w
!
Example oj screened room performance
requirement. Specifications NSA 65-6
100 dB
at isolating the test volume from the outside electromagnetic world. Both radiated susceptibility and
emission EMC tests can be conducted without
causing RF jamming problems to outside communications or being confused by the penetration of
ambient electromagnetic noise. There is, however,
a major drawback in the use of shielded enclosures.
Because the walls, floor and ceiling are highly
conductive and usually orthogonal or parallel, the
room becomes a high-Q, multifrequency resonator
where con1plex standing wave patterns can be set
up along all three principal axes.
The exact standing-wave patterns will depend
on the shape of the box, the positions of the
source antenna, the measurement antenna (or
EUT) and the frequency. Typical of the variation
in field strength which occurs inside these rooms is
that shown in Figure 9.6 [7]. The test configuration is that specified by MIL STD 462 RS03 and
the lower panel of the diagram shows that the
variability in the field strength at the E UT is at
least a factor of ± 1O. This order of uncertainty
will be present in all radiated susceptibility and
emission ITleaSUrements which are made inside a
simple undamped shielded enclosure. A study of
the effect of standing waves at frequencies below
100 MHz in a shielded enclosure against
equivalent open-range measurements has been
made by Stuckey et al. [8J.
Other investigators [9J have made confirmatory
measurements of predictions generated by a 2D
computer model of reflection proce,sses in
chambers. This model is based on amplitude and
phase reconstructions from distributed Hugens
158
I
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
GROUND PLANE
I
EUT
I
I
1 metre
1
FIELD GENERATING
~ / ANTENNA
a..------
\'''-'''l~
;. 1 metre
;.
1 metre
1 metre
t
FIELD MEASURING
ANTENNA
~~
SHIELDED ENCLOSURE
WA\
T~ CONTROL FIELD
~ 1 fetre
=10 VIm
100......----~------
E
_
80
3>
~
o
60
40
zw
20
c::
I-
en
10 ......&-..............-I-~........-I&o-l;.u...iY-~~ .....--Il........~
8
C
..J
W
iI:
6
w
~
U
Ci
4
c
~
sources on the chamber walls. A visual impression
of the complexity of a typical standing-wave
pattern at a single frequency can be gauged by
studying the model graphical output given in
Figure 9.7. This shows the calculated standing
wave pattern at 180 MHz with a centrally
positioned source in a 5 X 5 m (floor area)
reflective shielded chamber.
I t is possible to exploit the standing wave
properties of a simple shielded room to generate
high field strengths for limited input power [1 OJ
by using a special commercially available susceptibility antenna, known as the Cavitenna [11 J.
The device, when fixed to the inside wall of the
screened room, excites the entire room using the
structure as a ground plane to increase the
radiator's effective electrical size. Thus a 1.2 mlong antenna can produce equivalent field
strengths to a 5 m log periodic at a frequency of
30 MHz. The antenna is set up above the ground
plane bench as shown in Figure 9.8a; with the aid
of a levelling loop amplifier it can efficiently
produce the field strength from 30 MHz to 1 GHz
shown in Figure 9.8b with an average value of
25 V 1m for an input power of between 1 and 7 W.
Other techniques have been tried which aim to
-I
2
BENCH
11...-.........................L.......L...-&--&-................--L.--A..--&.--I---I.........L:.....I.
40 50 60 70 80 90 100 110 120 130 140 150 160 170 180190200
f---10 ft .-----.,
Variation offield strength at EUTfor constant
10 Vim control field. Location of aerials for
radiated susceptibility testing shown for
MIL STD 462 test method RS03
PLAN VIEW
t
.-
1
4181lr-
12 ft.
SCREENED ROOM
( no absorber)
FREQUENCY MHz
Figure 9.6
MONITOR
PROBE
.
r
11
SIDE VIEW
(a)
POWER INPUT
10
a:
00
~ ~~
STANDING WAVE PATIERN
3
L..-..:....;L..;...,;;..:....::...
~~
1
~~_--1 0
--'----:...--:....~
_---~~------------:-~ 50
:r:
1-_
rIJnl44+-I+I-1~'tWIA.1I~~....M~W.~. .W4WlJll.j 30
ww-
40 g~
E
u:g:::,
---if8
0
(f)
1 - - - - - - - - - - - - - - - - - - y - - - - - i 1 0 0 :r:
90 II
"
80
"
70 z~g ~ ~
40
30
20
10
~_-_-...,..:....:..__\"""-+_=_~~_+___1~~.L.I....,;",~-O
100 200 300 400
500
600 700
800
~>
Q-..J
u:
W
900 1000
FREQUENCY MHz
Figure 9.7
G'Ialculated E-jield standing-wave pattern in
square cross section screened room. 5 m-square
chamber with central source at 180 MHz
Reproduced by permission or NPL/HMSO
(b)
Figure 9.8
~]Jicient field strength generation in
undamped screened room using wall-mounted
,cavitenna)
EMC TEST REGIMES AND FACILITIES
mInImise the standing-wave problem in screened
rooms without the introduction of large volumes of
costly radio absorbent material. It has been
suggested [12J that asymmetrical shaped chambers
w here few of the reflecting surfaces are parallel can
be helpful in controlling the allowable chamber
modes, resulting in a reduction in typical field
variability in a rectangular chamber from +20 to
-40 dB to less than ± 10 dB.
The specification and purchase of a screened
room suitable for EMC testing is an important
task [13J and involves considerations which lie
beyond the immediate issues of size, shielding
performance, delivery and cost. I t is important to
consider the through-life operating costs of the
enclosure as daily use of this expensive hardware
will inevitably result in damage and maintenance
problems. These could be costly if the room and
particularly the doors and door seals are badly
designed or of poor q uali ty. Salati [14 J details
cost-effective maintenance for shielded enclosures
and suggests appropriate repair procedures.
9.2.3 RF anechoic screened chambers
9.2.3.1 Partial solutions
The most obvious way of suppressing the standing
waves inside a screened chamber is to cover all or
most of the reflecting surfaces with radio
absorbent material which can significantly
attenuate the reflected waves and prevent modal
patterns from forming. Unfortunately this solution
has two clear disadvantages:
(i)
(ii)
The cost is extremely high largely owing to
the material cost.
The working space in the room can be
substantially reduced by the absorber and
thus a larger and more expensive chamber is
required.
The full RAM-lined large chamber solutions are
only used in industries where the investment can
be justified, such as the aerospace or automotive
sectors. Small to medium sized chambers which
are more widely used in the electronics ind ustry
are often not equipped with RAM on cost
grounds unless mandated by appropriate test
standards. This has led to a number of low-cost
schemes being proposed [9, 15-17J which use
some RAM in special configurations to mi tiga te
the worst effects of standing waves on
measurement accuracy.
One concept [15 J is that of placing absorber
only on the back wall of the room, and building
an absorbing hood around the EUT as shown in
Figure 9.9. Such a configuration reduces the
sharp peaks and troughs infield strength
159
REFLECTED
WAVES
SCREENED ROOM
Figure 9.9
ABSORBER WALL
Hooded test area configuration in screened
chamber
produced by the standing waves to manageable
proportions. When used in conjunction with an
automatic field levelling loop, field variability of
around ±2 dB is claimed from 50 to 100 MHz and
better than ± 1 dB up to 550 MHz in a
4 X 4 X 2.5 m chamber. This test configuration is
useful for testing an E UT up to a half-rack size.
Another approach [16J is to damp out the
resonances by extracting energy with RAM at
standing wave sites of maximum field strength
within the room. The undamped frequency
response is shown in Figure 9.10 for a
2.5 X 2.5 x 5 m room with a first resonance at
75 MHz. Figure 9.11 shows how the first resonance
is reduced as the loading provided by the absorber
is increased with increasing conductivity.
Finally, this brief survey of low-cost techniq ues to·
reduce standing wave problems in screened rooms
by using only small amounts of RAM, includes a
suggestion made in 1981 [9J. This involves a
combination of the asymmetrical room concept
and that of strategically sited RAM in an elliptical
>
w 13
-co
(J)"O
0 ........
~o
:c:'
I-~
°0
mo
a:: a::
1-0
(J)w
oz
...Jw
ww
U:a::
()
(J)
50
200
FREQUENCY MHz
Figure 9.10
Frequency response of shielded room excited
with small magnetic loop
160
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
9.2.3.2 Full RAM solutions
Screened chambers with nonparallel walls, barnes
and angled planes are all a ttempts to either
minimise the amount of RAM required, or in the
past to compensate for poor attenuation
properties of RAM available at that time. With
the development of high-quality broadband
pyramidal RAM made by impregnating a carbon
carrying latex into a flexible polyurethane foam
plastic [18J it is possible to produce simple
rectangular chambers with good reflection
attenuation at an acceptable cost.
Anechoic chambers can be divided into two kinds:
>
w::O
0 ....
-co
00-0
ZO
I~
1-o~
zO
wO
0::0::
1-0
OOw
oz
...Jw
Ww
U:o::
u
Cf)
(i)
50
FREQUENCY MHz
Figure 9.11
Suppression of screened room resonance with
increasing RAM loading at the room centre
chamber. The scheme uses a RAM column sited at
the secondary focus. If the radiating antenna is
placed at one focus 'it can be seen in Figure 9.12a
that the calculated field strength peaks at the other
owing to the range/phase invariance properties of
the bounding ellipse. I t should then be possible to
remove energy efficiently from the system with
relatively small amounts of RAM placed at this
importan t location as indicated in Figure 9.12 b.
\
SOURCE
* Location of RAM
Figure 9.12
RAM column centre at
second focus of ellipse
Novel elliptical chamber design combining
asymmetric chamber and strategically sited
RAM (aj Focal source at 30 MHz - no
RAM (b j Small amounts of RAM placed
as shown
Reproduced by permission of NPL/HMSO
(ii)
Full anechoic facilities with quiet zones of up
to 1-3 m across and reflectivities as low as
-35 dB. These are specialist chambers used
mainly for measuring polar diagrams of
an tennas moun ted on vehicles, aircraft and
spacecraft.
Semianechoic chambers that reduce standing
waves to manageable proportions such that
reliable EMC measurements may be made.
These chambers sometimes have a reflecting
ground plane floor and simula te an openfield site for making CISPR, FCC type
measurements [19 J.
In the following text only chambers of the second
kind which are sufficiently anechoic to conduct
successful EMC tests will be addressed. The
performance of an EMC semianechoic chamber
(SAC) can be gauged by reference to a typical
example devised and built by IBM [20].
The
screened
chamber
dimensions
are
10.5 x 6.5 x 4 m with HPY-24 pyramidal absorber
[21] on three walls and the ceiling. Special thin
ferrite absorber NZ-31 [22J was placed on the far
wall and door which was the closest to the EDT
location. Standard EMC antennas such as biconics
and tuned dipoles were used to investigate the SAC
performance. Figure 9.13 shows the improvement
in chamber resonances after the room was equipped
with absorber. All the high-Q, peaks and troughs
are suppressed leaving a chamber which is within
± 1.5 dB of the equivalent open-range performance
at frequencies up to 230 MHz and within ±3 dB up
to 950 MHz.
Kuester et al. [23J have produced a theoretical
model for calculating the reflectivity of absorber
lined metal walls and this has been improved on
by Gavenda [24]. He used the simplifying method
of electrical images to allow calculation of the
field strengths after multiple bounce reflections in
a semianechoic chamber with partially reflecting
surfaces. The model still has considerable
limitations and cannot be used to completely design
the optimum SAC. However the model is helpful at
EMC TEST REGIMES AND FACILITIES
80
80
60
60
>:::1
-
>
~
(i)
co
CD
"0
"0
80
80
60
60
(ii)
(b)
(a)
80
80
60
-
>
>
~
~
CD
(i)
"0
::C
Q
co
::r
(c)
Figure 9.13
(i)
"0
S]
( d)
Antenna coupling plots made in IBM semianechoic chamber showing how absorber material suppresses
screened-room resonances (a) 30-80MHz (b) 80-130MHz (c) 130-180 MHz (d) 180-230MHz
( i) Before RF absorber (ii) After RF absorber
Reproduced by permission or IBM
low frequencies where the absorber reflectivity is of
the order of only -1 to -3 dB per bounce.
l'he performance of RAM is defined as the level
of reflected energy from a RAM covered surface as
compared with that reflected from the same area
of metal surface. The general construction of a
block of pyramidal broadband absorber is shown
in Figure 9.14. The height of the pyramids varies
from a few cm to 4 m depending on its desired
attenuation at low frequencies. Typical normal
incidence reflected attenuation as a function of
pyramidal absorber electrical thickness [25] is
shown in Figure 9.15a with the off-normal reflectivi ty shown in Figure 9 .15b. Figures for the reflectivity of a typical high-performance pyramidal
RA~1 as a function of frequency and pyramid
height are given in Table 9.2.
FOAM PYRAMIDS
/
FOAM BASE
Figure 9.14
Construction ofpyramidal foam RF
absorber
Reproduced by permission of' Emerson and Cuming
161
162
A HANDBOOK FOR EMC TESTIN"C AND MEASUREMENT
50.......-----r-----T---~--..
100 ------...-----....----.--.,.---.,,------.
~ 30
(0
~ 10
:>
i=
frl
~
20
z
~
..J
U.
~ 10
UJ
~ 1.0
0.01
0.1
1
:::>
10
I-
zUJ
THICKNESS IN WAVELENGTHS ( D / A)
~
UJ
(a)
0::
50 _---w'----r----r----.---r----r-~
~ 0.1
.,....,
«
UJ
~
co 40
"0
~ 30
:>
~
w
0.01 !o-----...Io----..I-----o 10 20 30 40 50
20
_
60
70
CHAMBER REFLECTIVITY ( - dB )
..J
U.
~ 10
Figure 9.16
O'--_--L_---L_ _--.L._--L._..L-~......L_~
.........
1
1.5
2
3
4
5 6 7 8 9 10
THICKNESS IN WAVELENGTHS ( 0 I A)
tivity of -20 dB is required at the lowest frequency
of interest. By reading off the electrical length of
the absorber for -20 dB reflection from Figure
9.15a and selecting the 150-in-high absorber in
Table 9.2 one can calculate that an anechoic
chamber fitttJd with this material would fulfil the
± 1.5 dB measurement uncertainty criterion at
frequencies as low as 16 MHz.
Semianechoic rectangular chamber ground
reflection EMC test ranges with reflections which
are sufficiently controlled to enable testing to FCC,
CISPR and VDE requirements at 3 m are commercially available [19]. Typical calibration curves
relating chamber performance to theoretical opensite range attenuation can be seen in Figure 9.17.
(b)
Performance graphs for pyramidal foam
absorber (a) Generalised reflectivity of
eccosorb VHP at normal incidence
( b) 0fJ-normal reflectivity of eccosorb
VHP. Eccosorb VHP is manufactured by
Emerson and Cuming Ltd
Figure 9.15
Reprod uced by permission of Emerson and Cuming
Lawrence [18J derives a graph which relates field
measurement uncertainty in an anechoic chamber
to absorber reflectivity. This is reproduced in
Figure 9.16 and indicates that for measurement
uncertainties of 1.5 dB, absorber which has a reflecTable 9.2
Measurement uncertainty as function of
chamber reflectivity
Example of the reflectivity ofpyramidal RAM as function of thickness and frequency
Guaranteed maximum reflectivity in dB
Material
120
MHz
VHP-2
VHP-4
VHP-8
VHP-12
VHP-18
VHP-26
VHP-45
VHP-70
-30
Non standard
VHP-110
VHP-150
-35
-40
200
MHz
300
MHz
500
MHz
1
GHz
3
GHz
5
GHz
10
GHz
15
GHz
24
GHz
-30
-40
-40
-45
-50
-50
-50
-30
-40
-50
-50
-50
-50
-50
-50
-40
-45
-50
-50
-50
-50
-50
-50
-45
-50
-50
-50
-50
-50
-50
-50
-50
-50
-50
-50
-50
-50
-50
-50
-50
-50
-50
-50
-50
-50
-50
-50'
-50
-50
-30
-35
-30
-35
-40
-30
-35
-40
-45
-30
-35
-40
-40
-45
-50
-40
-45
-45
-50
-50
-50
-50
-50
Eccosorb VHP is manufactured by Emerson and Cuming Ltd. Suffix number is pyramid height in inches.
EMC TEST REGIMES AND FACILITIES
50 _-----,r----r---r----r---~-.,..__-_y_-_,
45
~ 40
~35
~ 30
~ 25
w 20
~
15
Cii
5
~ 10
20
30
200 300
50
Typical calibration curve ofactual site
attenuation against theoretical site attenuation
(Performance ojsemianechoic chamber
designed to simulate open-area test site)
Reproduced by permission or Rayproor
SPECULAR REFLECTION POINT
FOR REFLECTED RAY
DIRECT AND REFLECTED
WAVEFRONTS IN PHASE
d~dr
ed~er
TAPERED
ANECHOIC CHAMBER
Figure 9.18
Narrow angle tapered chamber ensures
direct and reflected rays stay almost in phase
9.2.3.3 Tapered anechoic chambers
This design of chamber usually permits lower
frequency operation at a given reflectivity level
than for a similar sized rectangular design. The
source antenna is mounted at the apex of the
taper section and for taper angles of 30 degrees or
less the specularly reflected waves from the sides
of the taper are at grazing incidence to walls
resulting in little path difference between the
direct and reflected radiation [18J . Under these
conditions an almost unperturbed wavefront
propagates down the taper to the cubical working
volume as shown in Figure 9.18. This style of
chamber is not particularly suitable for EMC
measurements and is not widely used. I t is more
appropriate to antenna and other measurements
where a low reflectivity quiet zone rather than a
semicontrolled large working space is preferable.
9.2.3.4 Conclusion -
chamber in which to carry out EMC testing, some
assis tance is at hand. l'he commercial manufacturers have wide experience of actual installations
and the obtainable performance; they can advise
and are often able to offer turnkey packages which
will minimise the risks to the customer. A number of
review papers have been written dealing with
chamber design criteria [26, 27J and chamberj
anechoic material selection [28J.
1000
FREQUENCY MHz
Figure 9.17
163
9.2.4 Mode-stirred chambers
The problem of controlling, or at least minimising,
the measurement uncertainty caused by multiple
standing waves inside a reflective screened roonl
has been tackled in another way which is complementary to the 'absorption' approach. This
alternative technique deliberately maximises the
number of possible reflection modes which can be
sustained within a highly reflective chamber in an
effort to expose theEUT to all possible field
strength values at each frequency of interest in
the band being investigated.
This concept is known as mode stirring or tuning
and in the mid 1970s seemed to be a promising lowcost alternative to semianechoic chambers for EMC
testing. Much has been written with regard to this
concept [29-32J and a full understanding of its
technical basis is not a simple matter. The method
offers some potential advantages for EMC susceptibility testing in addition to lower cost than for a
semianechoic chamber. The main advantage
results from the wave polarisation being randomly
varied in the isotropic homogeneous field which
exists in the mode-stirred chamber [33J. With the
E UT immersed in such a field there is no need to
reorient it and repeat the test up to three times to
cover all polarisations.
The reverberating chamber, as it is sometimes
called, is also capable of providing efficient
conversion of source RF power to high field
strength for performing tests on large objects or
complete systems. There is then the clear potential
r------------
I
ANGLE POSITIONER-r.=======~~
I
I
MODE TUNER
I
anechoic chambers
For managers and EMC engineers who may be
faced with the responsibility of specifying and
selecting a screened anechoic or semianechoic
Figure 9.19
Example of mode-tuned enclosure systemJor
EMC measurements (NBS-US.fl)
Reproduced by permission or NBS
164
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
to reduce test time and cost as secondary benefits of
using a mode-stirred chamber.
A typical chamber configuration is shown in
Figure 9.19 with the mode stirrer constructed in
the form of multiple irregular shaped and sized
paddle wheels which are fixed to the walls or
ceiling and driven by stepper motors to ensure the
maximum number of possible chamber modes are
activated. The validity of this method depends on
the maximum number of chamber eigellmodes
being excited with a known mode density as a
function of frequency. The maximum number of
modes are generated when the chamber is large
compared with the frequency and this technique is
valid for frequencies of 200 MHz or above in
chambers of the order of 5 x 5 x 3 m. The
optimum design criteria for reverberating charnbers
are to make the volume as large as possible and the
ra tio of the squares of linear chamber dimensions as
non rational as possible [33J.
Reverberating chambers can be operated in two
ways:
Mode tuned where the paddle wheel is stepped
slowly through many positions within one
complete rotation at a given test frequency.
The time for which the paddle blades are
stationary is determined by the time it takes
the EDT to respond to the imposition of a
new stimulus.
Mode stirred where the paddle wheel is moved
continuously during the test at a given
frequency. In this case the rotation rate
should be slow enough for the EUT to
respond to the changing wavefield conditions.
(i)
(ii)
Typical field strength variability with frequency
for the NBS (US National Bureau of Standards)
chamber is shown as a function of frequency in
Figure 9.20 as measured by two different sensors.
45r---------------,.-----------,
E 35
>
CD
"'0
o
ill
25
AVERAGE FIELD
iI
()
a:
I()
~ 15
- - - Field from calibrated 1 em. dipole
- - Field calculated from receive antenna
ill
51....---------~------------i.
20
0.2
FREQUENCY GHz
Figure 9.20
Maximum and average electric field
strengths generated inside the NBS chamber
(empty) mode tuned)
Reproduced by permisssion
or NBS
The curves relate to the maximum and mean field
strength recorded at each frequency when the
chamber is mode tuned. It has been suggested
that mode-stirred or mode-tuned chambers can
be used for radiated emission testing [34J, but the
practice has not been taken up widely in the
EMC test community. Indeed, mode-stirred
chambers have not been as widely used for
susceptibility testing as predicted, probably owing
to the difficulty in relating the measurements
made in this way to the results obtained from
more conventional test methods.
Some measurements have been made in an
attempt to correlate susceptibility results obtained
using mode stirred and anechoic chambers, which
showed that the EUT response was less in the reverberating chamber than in the traditional anechoic
chamber test [35]. There are however, examples
where these chambers have been used successfully,
such as testing shielding effectiveness of cables and
connectors to MIL STD l344A method 3008 as
reported by Crawford et al. [36J at NBS.
9.2.5 Novel fatilities
When the systems to be tested are very large, such as
equipment for communication centres, computer or
telephone switching installations, it may not be
possible to provide economically conventional electromagnetically enclosed testing facilities such as
those previously described. Depending on the
amount of screening attenuation and minimum
internal reflectivity required to carry out the
particular tests, a number of unconventional
chamber solutions may be considered which
include large 'chicken wire' cages, metallised airinflated structures and underground caverns.
The chick-wire cage can be built from wood and
a metal wire mesh to provide large enclosed
volumes at low cost. The penalties include
achieving only moderate attenuation of around
40 dB at VHF and no suppression of internal
standing waves.
Metallised air-inflated structures are capable of
providing moderate to large volumes with floor
areas up to the size of a couple of tennis courts.
They are expensive to purchase but can be moved
to new locations and re-used many times.
Shielding is relatively poor 20-40 dB but this
approach is an option for testing large systems.
To my knowledge underground caverns have
been used for a number of EMC tests which
include spacecraft and commercial computer
systems. This approach can afford good screening
of better than 90-100 dB at most frequencies, and
with the addition of a small amount of RAM the
cavern can closely simulate the EM performance
of an open test site. The working volume is
EMC TEST REGIMES AND FACILITIES
165
usually inexpensive to hire or purchase as it
already exists as a byproduct of mineral
extraction. This makes the use of large
underground sites, which can have floor areas the
size of a football pitch, very cost-effective for
testing large distributed systems which may have
many interconnecting cables.
The main drawbacks to using a facility like this
are the usually limited shaft or roadway access,
the possibly high humidity environment and the
safety
and
evacuation
considerations.
An
underground facility may be an ideal solution
when a project is subject to costly multiple EM
requirements such as EMC, NEMP and Tempest.
a standard test under the ambient conditions at
each test site as this may be reflected in test costs.
In such conditions measurements may need to be
repeated and taken close in to the EDT (at 3 m).
This can lead to difficulties with extrapolation to
measurements made at other distances on another
site. Because of this difficulty, a problem could
arise if the measurements have to be checked by a
laboratory working on behalf of the regulatory
authority which is blessed with low ambients and
capable of measuring at 10 or 30 m. I t is therefore
preferable to use a test facility where the ambients
are low and measurements can be made directly
at 10 or 30 m.
9.3 Open-range testing
9.3.3 Testing procedure
9.3.1 Introduction
To make more consistent and reliable measurements, the ground at an open-air test range is
covered with a large metal plate or mesh to provide
a known constan t cond uctivi ty and dielectric
constant resulting in predictable RF reflection
properties. A typical mesh would extend for
60 X 30 m to give a lower working frequency of
20 MHz [37]. The mesh size d is determined by the
requirement d < AI10 where A is the wavelength at
the highest frequency at which the range will be
used. This is typically 1 GHz and so the mesh size
should be less than 3 em. It is important not ·to
obstruct the ground plane with buildings or test
equipment which can cause RF reflections, and for
this reason the receivers and antenna positioning
equipment are often located close to the receiving
antenna but under the ground plane. A similar
provision can be made for the mains supply and
support equipment for the EDT. An example of a
useful site configuration is shown in Figure 9.21.
The details of a suitable measurement site are
specified in the various regulations which apply to
the equipment being tested, and these must be
c'onsidered carefully by the site operators. In the
Open-site RF measurement is the traditional and
straightforward approach to making measurements
of the EMI characteristics of equipment. The
technique has been used for testing both civil and
military electronic equipment. Open range testing
became the norm for testing commercial equipment
with the advent of. the VDE and FCC regulations
for example, concerned "with the measurement of
radiated emission levels from household appliances,
office equipment and information technology
devices such as personal computers.
The test specifications and regulations governing
the construction and calibration of open test ranges
are dealt with fully in Chapter 2. The aim of this
section is to explore the construction, certification
procedure and operation of these facilities.
9.3.2 Test site
The ideal test site consists of an obstruction-free
ground area and hemisphere above it. The site
should be located well away from sources of electromagnetic noise such as power lines or air conditioning
plant
con taining
electric
motors,
thermostats etc. Ideally, the site should be located
in the countryside well away from all industrial
EM noise and broadcast transmitters. Some
screening of TV and VHF radio transmitters
could be afforded by a ring of hills covered with
trees which would surround the ideal test site. It
is not always economically viable however for
companies to set up a test facility at some distance
from their city based customers to take advantage
of the low EM ambients. The alternative is to
attempt to make sensitive radiated emission
measuremen ts in the presence of high level and
randomly changing ambient signals, and this can
be extremely difficult and time consuming.
Potential customers of such facilities should
enquire about the average tim.e taken to complete
NON-CONDUCTING
LOW DIELECTRIC CONSTANT
WEATHER-PROOF BUILDING
RECEIVING ANTENNA
\
~========:::::::?
o ==
Automatic
antenna
height
positioning
1-4m.
t---+-----I~
-EUT-
EUT SUPPORT
EQUIPMENT
USN & MAINS POWER
ARTIFICIAL
CONDITIONING FILTERS
GROUND PLANE
Figure 9.21
\
ANTENNA
POSITIONER
Example oj open-range test facility
166
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
diameter = 2d
----to-!
RECEIVING
ANTENNA
Area within the ellipse must be free
of all RF reflecting objects
Figure 9.22
Requirements for open-area test site. EUT
to antenna distance d can be 3, 10 or 30 m
context of this text on EMC testing consider as an
example the requirements specified by CISPR 22
(testing of IT equipment) which call for
adherence to CISPR 16 (specification of radio
interference
measuring
apparatus
and
measurement methods). (Details contained in
section 3 of the CISPR 16 Document.)
The size of obstruction-free area is determined
by the measurement distance (3, 10 or 30 m) with
a shape specified in Figure 9.22. The ground
plane often extends to cover the full obstructionfree area to give the best results. For test sites
where compliance is not possible, a minimum set
of req uiremen ts for free area and ground plane
are given and can be seen in Figure 9.23.
----------........
/"'/\
~m \
II ~3m~~ 3m · EUT II
\ TEST AE~AL
I
II
B
/'
\
'"
SURROUNDING BOUNDARY
'-- - \ - - - _.-/'
(aj
(bj
Figure 9.23
Minimum requirements for alternative test
site (a j Minimum alternative measurement
site (b j Minimum size of metal ground
plane. D
d + 2 m, where d is the
maximum test unit dimension;
W == a + 1 m, where a is the maximum
aerial dimension; L == 3, 10, or 30 m
Reproduced by permission of BSI
rrhe purpose behind the detailed E UT configuration/layout and the height scanning of the receiving
antenna required by many test standards is to
measure the maximum interference generated by
the equipment at each frequency of interest.
The EU1' shown in Figure 9.21 is placed either
in contact with the ground plane or at a distance
of 0.8 ill above on an insulating table if it is a freestanding item. All cables should be of the type
and length specified for the EDT being tested. If
the cables are very long they can be bundled into
30-40 cm-Iong bunches at the centre of the cable.
During testing the EDT is exercised in one of its
operational modes, the receiver is tuned to a
frequency within the band of interest and the
antenna is moved through a range of heights
usually from 1 to 4 m above the ground and the
maximum signal level is recorded. This is
necessary to measure the signal strength from the
EU1' at that frequency for the minimum site
attenuation. (This is considered later when
discussing site calibration.)
The EUT must be rotated on a turntable, or the
receiving antenna can be repositioned at various
compass points, to detect the maximum emission
as a function of azim u th angle if the E urf cannot
be rotated. The structure of the radiation field
emanating from an EDT is usually complex with
many peaks or deep nulls at various azimuth and
eleva tion angles for each frequency being radiated.
The ability of open-field measurement methods
to measure the maximum fields at each frequency
of interest has been studied in some detail
[38, 39J. I t is difficult to see how the accuracy of
open-site tests can be improved without more
frequent sampling of the emitted radiation
pattern from the EUT and thus further increasing
the protracted testing time.
The polarisation of the receiving antenna is
changed at each frequency and location to
measure the worst-case emission field strength. All
signal strengths should be measured using both an
average and quasipeak detector function on the
EMI receiver to fully cornply with CISPR 22. The
frequency is then changed and the test repeated
until the band from 30 to 1000 MHz has been fully
explored and the maximum field strengths
recorded. The operating mode of the EDT is then
changed and the entire test sequence is repeated.
If the recommended tuned dipoles are used as
the receiving antenna, their length must be
physically adjusted at each frequency above
80 MHz (for CISPR 22 and frequencies below
80 MHz a fixed length equivalent to the 80 MHz
tuned length is used down to 30 MHz). Other
specifications such as FCC part 15 require the
dipole to be tuned over the whole frequency band.
Clearly, the test time required for the multiplica-
EMC TEST REGIMES AND FACILITIES
tion of these measurement parameters is enormous
and simplifying procedures have to be adopted in
practical tests. The height positioning of the
antenna and the rotation of the EUT can be
automated with motor positioners. 'The frequency
bands can be rapidly scanned using automatic
receivers and the data quickly accumulated and
logged using a control computer. Only those
frequencies where the measured signal strength
approaches the specification level need attract the
full rigour of the test procedure to ensure that the
maximum field strength is measured.
All these measurements must be made in the
presence of ambient signals which ideally must be
at least 6 dB below the specification limit. At most
test sites this is rarely the case and computer
aided signal identification is often used to
recognise, mark and ignore some of the more
stable ambient signals from broadcast transmitters.
Broadband antennas such as biconics and log
periodics are permitted under most testing
regula tions and their use, together with scanning
receivers, can lead to a much more reasonable
testing time.
9.3.4 Site calibration
Site attenuation is defined as the ratio of the input
power to the transmitting antenna to the measured
power at the output of an identical receiving
antenna operating with a given polarisation when
both are located at known positions on the site as
in Figure 9.24. By measuring this attenuation as a
function of frequency it is possible to validate the
site for testing by comparing it with a reference
site which is usually operated by the government
metrology agency such as NBS in the USA or
NPL in the UK.
It can be seen from Figure 9.24 that the power
measured at the receiving dipole is a vector
combination of the contributions from the direct
path and the reflected path from the ground. The
167
amplitude and phase changes introduced into the
reflected path by the increased path length and the
addi tional phase change on reflection will produce
a systematic variation of received power as the
height of the receive antenna is changed. The site
attenuation at a given frequency j, range d,
transmi tter antenna height H t and polarisation is
the minimum value measured at a given H r where
the contributions from the direct and reflected
paths reinforce each other. Examples of calculated
site attenuation as a function of receiving antenna
height, at a number of frequencies for both
horizon tal and vertical polarisation, have been
made by Ma and Kanda [37J and are shown in
Figure 9.25.
By selecting the minimum attenuation from a
height scan at each frequency for horizontal and
vertical polarisations at the measurement distances
of 3, 10 and 30 m, one can plot a suite of site
attenuation curves shown in Figure 9.26 [40]. It
can be seen that the attenuation values (for the
NBS open range) vary from 20 dB at 30 MHz to
above 40 dB at 1 G Hz for 10m separation, and
that the relationship between attenuation and
separation at any frequency is approximately 20 dB
per decade. The calculated and measured values of
attenuation agree well at most frequencies.
5 .....- ........- .......---.~-...-- __- ......- -__- ...
J:
lI
<=>
iIi
I
97MHz 311 MHz 1GHz
430MHz
3
W
...J
0
c- 2
o
1
10
20
25
30
35
40
45
50
RELATIVE INSERTION LOSS dB
(a)
5....--........- .......----,~- .....-...,..----r--....--....
:I:
143MHz
44MHz
4
459MHz
1GHz
lI
o
W3
I
W
....J
~ 2
Ci
1 .....10
......15
......20
.......~-.......~..............~-- .....- .....
25
30
35
40
45
50
RELATIVE INSERTION LOSS dB
Figure 9.24
Open-area test site calibration setup
(horizontal polarisation). Site attenuation,
A == 10 log PI.N / POUT (max) for fixed
values of d == 3, 10 and 30 m and with
POUT ( max) selected from measurements
with receive antenna height H r == 1 - 4 m
Figure 9.25
(b)
Calculated open-area site attenuation with
frequency, height and polarisation
( a) Horizontal polarisation, (b) Vertical
polarisation. Source: M a and Kanda,
NBS-USA
Reprod Llced by permission or NBS
168
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
to 60
Cable and connector losses and VSWR
Position of EUT cables and peripherals
Nonuniform field strength/range relationship .
"'0
CJ)
Source height: 2m.
Vertical polarisation
~ 50
...J
•
5 40
~
0:: 30
UJ
30m
CJ)
~ 20
10m
3m
~
~
10
Z
~
0
101
102
(a)
103
FREQUENCY MHz
~ 60
CJ)
Source height: 2m.
Horizontal polarisation
~- 50
...J
5 40
~
ffi
30m
30
CJ)
~ 20
~
10m
:::>
~ 10
(b)
0
101
Figure 9.26
9.3.5.1 Reflections from objects
3m
z
~
In August 1985 a study (CISPR/B/WG/2) analysed
data gathered from a number of regulatory
authority test sites on a single item of computing
equipmen t measured during the previous year.
Dash [43J suggests that, as expected by some EMC
practitioners, the correlation between measurements from the various test sites was. poor, with a
standard deviation of 8.5 dB. This means that the
emission field strengths at anyone site can only be
predicted to an accuracy of around 30 dB (to a
95% certainty) based on the figures from any
other site. I t is therefore clear that although the
site attenuation may be measured quite accurately,
this does not mean that the EM C tests that are
carried out on the sites are equally accurate.
102
FREQUENCY MHz
103
Calibration of open-area test site (site
attenuation against frequency) (a) Vertical
polarisation) (b ) Horizontal polarisation)
• Measured data, Source height 2 m
Calculated data.
The performance of well constructed open-range
test sites has been widely reported, for example the
IBM Endicott facility [41 J, and general design
studies have been carried out by DeMarinis [42J.
9.3.5 Measurement repeatability
The estimated worst-case uncertainty in defining
the range attenuation as calculated by the NBS
[37J is ± 1.2 dB. The worst case difference
between measured and calculated site attenuation
is given as 1 dB for horizontal and 1.9 dB for
vertical polarisation. These figures may be true
for a carefully controlled government establishment range charged with setting standards for
industry, but published evidence suggests that the
everyday problems encountered at industrial test
sites make this accuracy difficult to achieve.
1-'he following factors affect the measurement
accuracy on an open site:
Reflections from objects
Nonconductive weather cover structures
Antenna impedance and VSWR changes with
height
An tenna size field averaging
Balun VSWR and losses
Differences in commercial antennas
An indication of the effects of reflections at the
boundary of a 10 m measurement site can be
gauged by calculating the modifications to the
normal site attenuation curve when a large metal
pIa te with its long axis parallel to the
measurement axis is introduced on the site
boundary. The errors are reported [42J to be
± 1.5 dB with the plate at 15 m and ±0.5 dB when
the plate is 60 m away from the measurement
axis. Measurements have also been made with
trees 15 m from the edge of the range area which
introduced errors of 1-2 dB at certain frequencies
around 80 and 180 MHz [42J. From these data it
would seem that reflections from objects outside
the stipulated flat object-free area can contribute
between 1 and 2 dB to measurement uncertainty.
9.3.5.2 Weatherproof covers
Some open test ranges provide a weatherproof
shelter over the test area in which the EUT is
mounted so that testing is not compromised by
bad weather. The construction of these shelters
has been investigated as a possible source of
measurement error due to reflections from their
walls and roof. The use of various materials in
shelter construction has been investigated [42J
and crude measurements of reflection coefficients
have been made and are given in Table 9.3. This
shows that pinewood is a poor rna terial to use
while plastic and glass fibre sheets have low
reflection coefficients.
However, Dash and Straus [44J show that
dielectric constant and thickness, not conductivi ty, maybe the key factors in determining the
suitability of materials for EMC test site shelters.
Wood has a relatively low dielectric constant of
EMC TEST REGIMES AND FACILITIES
Table 9.3
Examples oj RF reflection coefJicients oj
number oj materials commonly used in EUT
covers on open-area test range
Material
Yellow pine plywood
Fir plywood
Waferboard
Drywall or sheetrock
Acoustic ceiling material
Composite wall w/fir plywood,
sheetrock, fibreglass insulation,
and cedar clapboard siding
Composite wall as above, but with
asbestos roof shingles
Composite technology plastic and
glass fibre wall with foam insulation
Reflection
coefficient
0.45
0.27
0.25
0.23
0.09
0.3
169
HEIGHT OF THE CENTRE OF VERTICAL HALF-WAVE AERIAL
ABOVE THE GROUND (in wavelengths)
0.25 0.3
0.4
0.5
0.6
0.7 0.75
100
a
90
ui 80
0
Z
«
ten
70
Ci5
w 60
a::
z
0 50
i=
«
CS
«
a::
40
30
0.27
o
0.03
0.1
Figure 9.27
1.3-2.5 [45J but plastics have values from 1 to 5
and must be used with care and only in thin sheets.
Site attenuation measurements in the presence
of an EDT shelter made from radome plastic
rna terials [46] has shown some evidence of a
change in the maxima and minima of the height
scan pattern (Figure 9.25). This effect is not
noticed when these data are processed into the
range attenuation plots, as only the minimum
attenuation figure is used. The presence of the
plastic shelter has altered the physical position of
the minimum attenuation path on the range. An
overall estimate of the errors introduced by a well
designed weather cover are of the order of ± 1 dB.
9.3.5.3 Antenna impedance changes with
height
The change of antenna impedance with height can
be thought of as being due to the interaction with
its image created by' the ground. The closer the
antenna is to the ground the greater is the mutual
impedance effect. The resistive component of the
impedance of a vertical and horizon tal halfwave
dipole antenna above the ground is shown in
Figure 9.27 [4 7J. The vertical dipole is well
behaved at a height greater than half a
wavelength, but the resistance of the horizontal
dipole is still changing from 60 to 80 ohms when it
is a full wavelength above the ground. If the
antenna impedance changes there will be a
mismatch with its balun, connecting cable and
the receiver input. Thus the voltage across the
receiver input port will be unknown and this will
introduce an error into the measurement. For
example, the measurement uncertainty due to
antenna mutual impedance/VSWR changes in a
horizontally polarised biconic antenna 1 to 4 m
0.2 0.3 0.4 0.5 0.6
0.7 0.8 0.9 1.0
HEIGHT OF A HORIZONTAL HALF-WAVE AERIAL
ABOVE THE GROUND (in wavelengths)
Variation oj radiation resistance with height
above ground Jor vertical and horizontal
polarised ha1jwave dipole
Reproduced by permission of RSGB
above the ground over the frequency range 30-300 MHz has been shown be ±2 dB or more [48].
9.3.5.4 Antenna size
field averaging
This has been discussed in Chapter 6 in relation to
the difference in field strength measured on an open
test site with a point source at 3 m, when using a
short CISPR 80 MHz dipole/or biconic as
compared with a 30 MHz FCC tuned dipole.
Figure 9.28 shows the antenna sizes in relation to
5m
W
>
°c~o-~
....Z
:;
....Z
-e
0
Size of 30 MHz
tuned dipole ____
4m
°o.."C
-
W
(J)
(I)
E
~W
E
0::Cl')
:::>-
3m
Size of CISPR 80 MHz
tuned dipole or bicon ic
antenna
2m
~
C/)W
~Z
We:(
~...J
80MH~ A
LLo..
0°
....
z
:c:::>
0°
_0::
1m
B
~o
5
10
15
20
25
30
dB (arbitrary scale)
E FIELD MEASURED AT A POINT
(source is at a distance of 3m.)
Figure 9.28
Field averaging with large dipoles. Field
exposed to: A == CISPR/bicon,
B == 30 MHz dipole
170
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
the field profile as a function of height [49J. The
larger 30 MHz dipole averages the 17 dB field
variation along its length and indicates a field
strength which is 8.5 dB lower than the actual field
strength at a height of 1 m. The shorter CISPR
80 MHz dipole and the biconic only have a 3 dB
field variation with length and make a reasonably
accurate measurement of the real field strength.
9.3.5.5 Balun VSWR and losses
Chapter 6 concluded that the typical VSWR for a
commercial biconic antenna was between 1.5 and
4: lover the frequency range 30 to 300 MHz
compared with a Roberts tuned dipole of less than
1.5: 1. Clearly the higher VSWR of the commercial
an tenna will result in greater measurement
uncertainty as the antenna impedance varies with
height. The loss in a typical commercial balun for a
biconic antenna is in the range 0.5--2 dB (30300 MHz) vvhich reduces the minimum detectable
signal in the band compared with that obtainable
with the Roberts tuned dipole balun which has a
loss of only 0.1-1 dB (30 MHz-l GHz).
9.3.5.6 Differences in commercial antennas
Work carried out at Hewlett Packard open test
ranges [50] has shown that range calibrations can
vary by up to ±6 dB when carried out using various
combinations of log-periodic antenna pairs. The
antennas are all manufactured to the same design
by a single company and differ only in serial
number. The errors are usually confined to a few
frequencies between 300 MHz and 1 GHz where
sharp response variations are observed over a
hundred MHz or so at up to ±6 dB and may be the
manifestation of antenna/cable matching problems.
l'hese effects are not observed when using tuned
dipoles for range calibration, but these are slow to
use and a wide band antenna is preferred. One
solu tion is to fit 3 or 6 dB pads at the an tenna
output when using complex wideband antennas
such as the log-periodic or biconic to help control
VSWR problems. The effect of a simple fix such
as this is a reduction in measurement sensitivity:
the preferred solution is to produce wideband
antennas with high-quality baluns with close
manufacturing tolerances. Investigative work such
as this on the properties of antennas, indicates
that the EMC test engineer can take nothing for
granted when attempting to make accurate
radiated emission measurements and should make
every effort to carry out measurement checks.
9.3.5.7 Cable and connector losses/VSWR
Investigations carried out by workers at Digital
Equipment Corporation in the USA [51] have
shown that significant errors of up to 10 dB can
be introduced by the change in position of the
antenna cable during a test. This effect has been
attributed to two causes. T'he first is the cable
acting as a parasitic element close to the antenna
which modifies its properties, and the second
more serious cause is due to leakage between the
cable and antenna elements due to imperfect
current balance and leaky connectors. Broadband
dipoles have shown relatively poor balun isolation
resulting in 6-10 dB errors. Again, large
differences in balun performance were discovered
in similar biconic antennas with different serial
n urn bers [51] . Some of these effects can be
reduced by placing a common mode ferrite choke
over the outer of the antenna coaxial cable to
suppress unbalanced current flow.
9.3.5.8 EDT cables and peripherals
Most of the 30-40 dB possible uncertainty between
radiated emission measurements on the same EUT
at different open sites [43] cannot be accounted for
by a combination of the 1- 1-0 dB errors resulting
from the issues discussed. The ANSI C63 study
group was set up in 1985 to examine the problem
of variable cable layouts in FCC MP-4 and
CISPR 22 tests on IT equipment. The wording in
these standards regarding placement of cables and
peripherals calls for their placement to find the
worst-case emission levels. This allows each test
site to place the EUT components in different
positions in search of the worst case emission
configuration. This will result in different
radiation patterns and different test results. The
working group therefore considered that certain
combinations of definite fixed cable placements
and peripherals should be prescribed. This
approach sacrifices the ability to find the absolute
worst-case emission levels but increases the test
repeatability. The details of suggested cable and
peripheral placement are inappropriate for listing
here but are given by Dash [43].
9.3.5.9 Nonuniform field strength/range
relationship
Within the CISPR 22 standard, para 9.4 relates to
measurements in the presence of high ambient
signals. It permits measurements to be made at
reduced distances from the EUT to increase the
measured signal level in an attempt to overcome
the masking ambient signals from broadcast transmitters and the like. The regulation permits the
scaling of the specification limit in a linear
manner with measurement distance.
This procedure is highly suspect when
conducted in an EM radiation field of complex
EMC TES1' REGIMES AND FACILITIES
configuration where the far-field boundary
distances for components at different frequencies
are not well known. The site attenuation curves
as measured with two similar dipole antennas do
show a simple field strength/range scaling law.
However, work carried out in Japan by the
Matsushita Company [52J to derive the site
attenuation curves using EDTs with realistic
radiation patterns and wavefield impedances has
shown that the 20 dB/decade scaling law is
inadequate. The test set up is shown in Figure
9.29a and the range a ttenua tion curves in Figure
9.29b. The correction curves from 3 to 10 and
30 m are shown in Figure 9.30 and differ from the
assumed 10 and 20 dB by up to 8 dB at 80 MHz.
\ITEMI
EJ
1
METER
hr
(a)
60
ht = 1m.
50
CD
"C
z
hr = 1 to 4m. (0 = 3m., D = 10m.)
hr = 2 to 6m. ( 0 = 30m.)
D=30m
40
0
~
:::>
Government regulatory agencies such as the NBS
can construct open-range test sites for making
radiated emission measurements at 3, 10 and 30 m
with site-attenuation performance close to the
theoretical values. The open-range radiated
emission test methods as defined by regulations
such as FCC, ClSPR and VCCl are time
consuming to carry out fully, and the presence of
EM ambient signals is an additional problem.
The foregoing discussion relating to open-range
emission testing shows that the practising EMC
test engineer and customers need to be aware of
the sources of uncertainty that can undermine the
most strictly regulated test regime. These
problems all stem from the attempt to make
extremely detailed and difficult electromagnetic
measurements of complex unknown wavefields by
using simple test equipment and quick procedures
which result in affordable testing.
EMC testing provides an indication of emission
levels from an EDT when measurements are
carried out to a standard proced ure. I t is not an
attempt to make full and accurate measurements,
with a close estimate of associated uncertainty,
irrespective of the time and cost involved.
'The overarching aim of con trolling the increase
in EM emissions from electronic equipment
probably justifies these less than rigorous but
economically acceptable test methods.
9.4 Low-level swept coupling and
bulk current injection testing
20
~
10
0
20
9.4.1 Introduction
1000
100
FREQUENOY MHz
(b)
Figure 9.29
Typical open-area test site calibration oj'
range attenuation (a) Site attenuation
parameters (b) Site attenuation for 3) 10
and 30 m (horizontally polarised) .
ht == 1 m) hr == 1 to 4 m (D == 3 m)
D == 10m)) hr == 2 to 6 m (D == 30 m)
CD 30t---~-----~--------------
Measured
correction factor
"C
Z
20
z 10
w
Or--20
/
---.L
Measured correction factor
100
~
«J=
9.3.6 Comments on open-site testing
30
z
w
o
~
:::>
171
1000
FREQUENCY MHz
Figure 9.30
Measured conversion factors to normalise
measurement distances of 30 m and 10 m to
3m
These two techniques are distinct but complementary. They have evolved together over the last 10
years in the UK, primarily in conjunction with
immunity clearance of aircraft [53J, military hardware and automobiles. The two techniques have
become popular throughout the EMC community
and are being taken up in the USA and elsewhere.
Several bulk current injection (BCl) tests have been
incorporated into the UK DEF STAN 59-41 EMC
requirements for triservice military equipment.
The low-level swept coupling tests are normally
carried out on complete systems to establish the bulk
or common mode induced current spectrum on a
cable loom for a given external EM field as it is
swept in frequency from about 5 to 400 MHz. This
induced current can then be scaled with external
field strength to derive the expected current in the
cable loom which would be induced by the specified
field to which the system must be immune. This
current can then be injected into the loom in the
BCl test at levels equal to or above those corresponding to the specified immunity level. By directly
172
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
injecting current into the cables it is possible to
simulate to some extent high-level free-field radiated
susceptibility tests but using only a fraction of the RF
power required to drive large antennas. This means
that it becomes possible to carry out technically
meaningful immunity tests on large systems at an
economic cost.
9.4.2 Low-level swept coupling
Consider an electromagnetic wave incident on a
complex system as shown in Figure 9.31. The
diagram shows the possible coupling routes by
which EM energy can interact with and propagate
through the structure and its apertures to the
semiclosed metal equipment box which contains
circuit
boards
populated
with
susceptible
components. The size of box apertures, circuit
boards and components dictates that they will be
electrically short at wavelengths much longer than
--
1
WAVE FIELD+SYSTEM STRUCTURE & CABLE COUPLlNG+SUSCEPTIBLE
I
BOX or BOXES ~
MAIN COUPLING PATH UP TO ~ 400 MHz
I
I
I
..
I ~F wove Incident
I
their physical dimensions and exhibit poor coupling
efficiency. These direct wave to component
coupling paths are therefore secondary at all but
the highest frequencies beyond about 0.5 GHz.
The main coupling path is provided by the
conducting system structure and the extended
cable runs within it. This route predominates for
all frequencies up to about 400-500 MHz for
systenls which are between 2 and 10 m long. The
simplified coupling scheme showing only the
structural and cable coupling route is given in
Figure 9.32 where the unknown individual
transfer processes within the structure and cables
are represented by a series of complex frequency
dependent impedances.
At present no real credence can be given to E- and
H-field measurements made in the restricted spaces
inside cOlTIplex systems such as aircraft [54] and
automobiles using triaxial sensors or other probes.
This situation, together with the limitations in
field on system
structure
i RF curr?nt 1\
pattern In ,\
s!ructu~e
diffraction
fields
Internal mutual
impedance
Multi-eonductor
transmission
coupling to
wiring loom
line response to
coupled energy
I
curren~
delivered
I
I
via sy.stem cabling.
(Dominates susceptibility up to 400MHz)
I
RF
t~ suscephble tJ.ox
SECONDARY
COUPLING
/' PATHS ""
Direct pick-up
by exposed
wiring loom due
to apertures
in structu re.
Figure 9.31
Schematic ofpotential RF coupling paths into system
WAVEFIELD
PARAMETERS
E
IH
TEST POINT uTP1 u
=VIm ~AVEFIELD
1
TO BULK CABLE CURRE T
TRANSFER FUNCTION ( mAl VIm)
=AIm
Z=o
2
I pO=W/m !
II
STRUCTURES & CABLES
2 - 10m long
..
-current in rnA
I
RF CURRENT FLOW
I
Za /
INCIDENT
WAVEFIELD
CIRCUIT BOARDS
BULK RF CURRENT ( located .inside the
IMPEDANCE NETWORK
PROBE
susceptible box)
representing each step in coupling path
Figure 9.32
Main structure and cable dependent coupling path (up to
~400
MHz)
EMC TEST REGIMES AND FACILITIES
computing multiconductor transmISSIon line
responses, leads to severe problems in tracing the
RF energy through the coupling chain to the
susceptible box.
I t is possible to measure the incident E- and Hwavefield cOlnponents and to determip.e wave
impedance, polarisation and angle of incidence on
the structure. I t is also easy to make an undisturbed
measurement of the bulk or common-mode cable
currentat the test point 1'P l, close to the connector
on the box of interest which contains the susceptible
circuits. See Figure 9.33. If the incident field
strength is kept constant while the frequency is
changed we are able to measure a swept frequency
coupling response of the system under test.
For example, the induced current in an aircraft
cable harness for a 10 V 1m external field is
presented in Figure 9.34 [54] and shows
maximum coupling at a frequency corresponding
to the resonant electrical length of the structurel
cable harness. Coupling factors for various cables
connected to a personal compu ter are shown in
Figure 9.35 and are typical of a wide variety of
equipments, having peak values of a few mA/V 1m.
173
The test set up for n1easuring low-level swept
coupIing to a system under test is shown in Figure
9.36. The first step in the test procedure is to
generate a levelled field at the test location [55].
This is done by placing the fibre-optically coupled
field sensor at the location where the E UT will be
and then generate in the control computer a set of
amplitude values for the tracking generator
attenuator for which a constant field strength is
produced. The same values will be used when
radiating the swept signal to ensure that the EUT
is subjected to the calibrated levelled field. The
distance from the broadband antenna to the EUT
should be sufficient to ensure that the EUT is in
the far field at all frequencies of interest.
A current probe which is connected to a fibre
optic transmitter is placed around the required
cable loom close to the connector on the
C/P ON VIDEO CABLE
C/P ON COMPUTER MAINS LEAD
EE
~
--
~
2
E
~
z
a
i=
()
OI:.:L-.
0
Z
CURRENT PROBE
measuring bulk cable current
\
crex:
fi
EQUIPMENT
UNDER TEST
"""""""
200
~
100
100
C/P ON DISC BUS CABLE
C/P ON PRINTER BUS CABLE
~
200
FREQUENCY MHz
FREQUENCY MHz
4f-'
«
ex:
l-
t?
6
~~2~
E
()
o
FIBRE OPTIC TX
CONTROL FIBRE TO ~
---DATA FIBRE
F.O. TRANSMITTER
carrying bulk current signal
to fibre optic receiver
Figure 9.33
-
o
100
200
FREQUENCY MHz
Figure 9.35
Examples of coupling transfer functions for
various cables on personal computer system.
( CIP == current probe)
Measuring bulk cable current with isolated
current probe and fibre-optic transmitter
CURRENT PROBE AROUND FIBRE OPTIC WIDEBAND
CABLE OF INTEREST
~ELEMETRY SENDER
40---------r----.....----------~
STANDARD FIELD
MEASURING SENSOR
0.
0.
c:(
E
Used to "pre-calibrate"
the field at the test ~
object location. (Derive
a power table and
store in the control
computer.)
30
==
IZ
ill
a:
a:
:::::>
()
20
..J
()
Q
"/ "'""-
BROADBA~ND
ANTENNA .....
CD
c:(
w
S~C~~~~ _D~;T~CE
FIBRE OPTIC LINK
ill
"'" . . . . . .
~
~
~ ....... ~
10
()
:::::>
Q
If
~
5
Figure 9.34
FIBRE OPTIC
RECEIVER
L----+-A
U ~j
25
Typical bulk current induced into cables in
aircraft. Incident field strength 10 Vim
horizontal polarisation
FIBRE OPTIC
~
10 - 100 W
0
",""
TRACKING
GENERATOR
Figure 9.36
CONTROL
COMPUTER
PLOTIER
Whole vehicle low-level swept-jrequency
coupling test
174
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
-10
FRONT OF VEHICLE
FRONT OF VEHICLE
«
co -20
"0
UJ
co -30
...J
«
()
~
-40
I-
z
UJ
0::
0::
::>
()
-50
-60
Q
UJ
()
::> -70
Q
~
FREQUENCY = 60 MHz
-80
20
40
60
80
100
120 140
160 180 200
Figure 9.38
FREQUENCY MHz
Figure 9.37
Typical induced cable current in complete
vehicle
susceptible electronics box and the control
compu ter rep rod uces the levelled field as the
frequency is scanned from about 5 to 400 MHz.
The received fibre optic signal is converted back
to an analogue electrical form and fed to the
spectrum analyser which is driving the tracking
generator providing the stimulus signal. The
spectrum analyser raw data are corrected for the
current probe transfer impedance and the true
cable induced current is displayed as a function of
frequency on the computer monitor. Typical
ind uced currents in the looms of a vehicle are
shown in Figure 9.37 for an incident levelled field
strength of 20 Vim. Note that the maximum
coupling value is 1.5 mAIVlm at 50 MHz
(-30 dBA at 20 V 1m) for this vehicle.
The production of a field to curren t coupling
curve enables the EMC engineer and product
designer to have an overview of the electromagnetic coupling properties of the EDT. I t is
common for coupling curves to be of the form
shown in Figure 9.37 where the coupling increases
from a low level at low frequencies (where the
EDT is electrically short) up to a maximum at
near structural resonant frequencies and then to
show a number of higher order coupling responses
in the region where the EDT is electrically long.
I t is interesting to investigate and understand
the physical properties of the EDT which
influence the coupling. 1'his can be done by
selecting a frequency of interest, such as 60 MHz
in the case of the coupling curve shown in Figure
9.37 (which is in the frequency range of
maximum coupling) and rotating the EDT while
recording the induced current. In this way, a
'pick-up' polar diagram can be produced, the
in terpreta tion of which can often reveal those
aspects of the E UT structure which are
determining the system coupling. Figure 9.38
shows these polar diagrams for a saloon car at
FREQUENCY = 160 MHz
Wavefield coupling polar diagrams with
current probe monitoring pickup in engine
management cable harness
- - V polarisation
- - H polarisation
60 MHz (1st resonance) and 160 MHz (well
above 1st resonance) for both vertical and
horizontal polarisation. Notice how at 160 MHz
the maximum coupling to a cable which is being
measured (located under the bonnet), occurs
when the field is incident on the front of the
vehicle. 1'his is not seen at 60 MHz where the
w hole vehicle is resonant.
The use of spot-frequency coupling polar
diagrams can be well illustrated with an example
of a less complex structure than a saloon car
which has many different sized door and window
apertures. Figure 9.39 shows the coupling
response from external field to a cable loom in a
miss.ile. The physical structure of the missile can
be represented by a short fat electrical dipole with
the centre load termination being the impedance
of the fore body to motor body mechanical joint.
Generating the polar diagram at the frequency of
maximum coupling produces the response shown
0
«
co -10
"0
I-
z -20
UJ
0::
0::
::> -30
()
UJ
...J
co -40
«
()
0
UJ
-50
()
::>
0
~
-60
-70 ' - - - I I - - - - - - l l - - - - - L _ . . . . - L . _ - - ' - _ - - - ' - _......._ ..........
............
40 50 60 70
80 90 100 110 120 130
FREQUENCY (MHz)
Figure 9.39
Example of RF current induced in system
main harness as function offrequency.
Swept frequency field strength == 20 Vim
EMC TEST REGIMES AND FACILITIES
TAIL
175
PICK UP PROBE
\
\
EUT MALFUNCTION LINE
(automatic indication)
Figure 9.41
HEAD ON
Figure 9.40
Coupling polar diagram oj system at
primary resonance Jrequency shows dipolelike response
In Figure 9.40 which is almost perfectly dipolar.
This shows that the missile has minimum
coupling when the field approaches head or tail
on and has a maximum repose when it is
broadside on. This is indeed the response of a
dipole and so this experiment confirms that the
main coupling feature and electrical structural
model of the missile is that of a simple dipole.
Such information can be used to suggest coupling
red uction schemes and is very useful in assessing
the electromagnetic compatibility of systems in
their expected operational environment.
9.4.3 Bulk current injection
When the indilced bulk cable current coupled
from an external wavefield has been determined
using the LLSC technique, the scaling factor from
the LLSC test level to the specified immunity
level can be applied to the measured induced
current. This level can then be injected into the
loom under test via a high power current
injection probe and the EDT observed for signs of
malfunction. Much has been written about the
advantages and technical justification of this
technique [56-59J and it is not possible to review
all the work here. Space permits only a brief
explanation of the key points involved in BCI
measurements. The test setup for an automatic or
semiautomatic bench test on an EDT is shown in
Figure 9.4l.
The control computer sets the frequency and
adjusts the power level to the injection current
probe. The forward power is monitored and
recorded for reference. The injected current is
increased until the EDT malfunctions and the
Operator intervention via keyboard
when EUT malfunction is observed.
(If no automatic link is possible.)
Example oj automatic bulk current injection
test corifiguration
control compu ter records the current flowing in
the loom as measured by the pickup current
probe via the spectrum analyser. The current'
readings are then corrected for pickup current
probe transfer impedance. The injected current is
reduced and the current at which the EDT
reverts to normal operation (if it does) is recorded
automatically by the computer. The process is
repeated as each new frequency is tested until the
whole band of interest has been covered.
An example of the output of an automated BCI
test on a microprocessor based electronics unit is
shown in Figure 9.42 where failures occur for bulk
cable currents of around 10 rnA flowing in the
rnulticond uctor unscreened cable.
Experiments [60J have shown that when the
injection and pickup curren t probes are
positioned as shown in Figure 9.41, and as
specified in DEF STAN 59-41, the measured
cable current is very nearly equal to the current
-10
J:-
U«
-20
~:::
-30
:fen
!;(cn
..... 0::
z::::>
O -40
w
0::0
0:: 0
::JZ
uo
-50
~~
Ur!
-60
~p=
o...J
we:(
u:2
-70
- -
::JI-
0::::>
~w
-80
-90
20
Onset of failure
- Release of failure
40
60
80
100
120
140
160
180 200
FREQUENCY MHz
Figure 9.42
Example oj injected current level as Junction
ojJrequency at which microprocessor vehicle
engine management system is disrupted
176
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
in the box under test for bulk current injection,
and that this is also true for direct illumination by
a wavefield. This gives confidence that the results
obtained via BCI tests can be related to
operational exposure of the equipment to EM
fields. Lever [61] has shown good correlation
between BCI system-induced failures and those
experienced during 'normal' radiated susceptibility measurements on automobiles. The BCI
technique has also been adapted for use in
development testing and assessment of a wide
range of electronic systems including IT
equipment [62]. In this case the injection probe is
constructed from two inexpensive ferrite C-cores
and the stimulus is provided by a pseudorandom
sequence generator which provides a broad
spectrum ou tpu t.
Having described them separately, the LLSC
and BCI measurement techniques can now be
brough t together to show how cost-effective
immunity testing can be carried out on large
complex systems such as aircraft, automobiles and
commercial vehicles for which standard radiated
susceptibility free-field testing may be prohibitively expensive.
The LLSC coupling data are scaled by the ratio
of the test field ( 1-10 v 1M) to the specified
immunity field (say 200 Vim) and the scaled
induced current is plotted as the lower curve in
Figure 9.43. The results of the BCI test, which are
a set of cable currents as a function of frequency
at which the EDT is compromised, are plotted on
the same graph as the upper curve in Figure 9.43.
The margin of safety between the available
current in the looms for the specified field level
and the required current for a failure is a direct
measure of the degree to which the immunity
specification is exceeded. This conveys far more
information than a simple traditional radiated
susceptibility no fail test at the specified field
level. The BCI and LLSC tests can permit the
careful optimisation of EMC safety margins above
the specified limit for production items, by
gathering information on the statistics of
variability of system coupling from the LLSC test
and on the failure current as measured by the
convenient BCI test.
9.5 References
2
3
4
5
6
7
8
50
Bulk cable current
required for unit
malfunction
40
E 30
t-
9
\
Induced bulk cable
current for "X" VIm
(coupling measurements)
«
Z
W
a:
10
0:
:::> 20
0
10
11
0
0
50
100
200
FREQUENCY MHz
Figure 9.43
Deriving susceptibility safety margin from
bulk current injection and bulk current
coupling measurements
12
WHIl'E, D.R.J.: 'A handbook series on electromagnetic interference and compatibility, vol. 2, Test
methods and procedures'. Don White Consultants,
Germantown, Maryland, USA, pp. 3.7-3.23
FARSI, M.: 'EMIjRFI shielding: theory and
technique'. Interference Technology Engineer's
Master, 1988, pp. 228---238
WHITE, D.R.J.: 'A handbook series on electrornagnetic interference and compatibility, vol. 3'. Don
White Consultants, Germantown, Maryland, USA,
1973, p. 10.75
Low-frequency cylindrical screened
chamber
14 m dia. x 12 m high, constructed for GEOS
spacecraft programme 1973-6. BAe Dynamics Ltd,
Filton, Bristol, UK
MIL STD 285: Attenuation measurements for
enclosures, electromagnetic shielding for electronic
test purposes, Method of, 25 june 1956
CARDENAS, A.L.: 'The examination of standards
for testing RF shielded enclosures', EMC Technol.,
jan-Feb 1988, pp. 26-38
CARTER,
N.J.
and
THOMPSON, j.M.:
's.usceptibility testing of airborne equipment
The way ahead'. 2nd symposium and technical
exhibition on Electromagnetic compatibility) Montreux,
1977, pp. 83-88
STUCKEY,
C.W.,
FREE,
W.R.
and
ROBERTSON, D.W.: 'Preliminary interpretation
of near field effects on measurement accuracy in
shielded
enclosures'.
Proceedings
of IEEE
symposium on EMC, 1969, pp. 119-127
BENHAM, G., COLEMAN, C and MORGAN, D.:
'Development of an elliptical anechoic chamber'.
Final report BT11868 of contract NPL196j0060,
1981, BAe Dynamics, Filton, Bristol, UK
SHEPHERD, D.R. and GOLDBLUM, R.D.:
'Exploiting shielded room characteristics to provide
a low cost, semiautomated test system for EMS and
EMV testing'. Mikrowellen Mag., 1982, 8, (6),
pp. 714-718
Cavitenna AT2000, Accessories for RF testing.
Amplifier Research, 160 School House Road,
Souderton, PA 18964-9990, USA
EDWARDS, D.J. and BURBIDGE, R.F.: 'An
experimental investigation into the performance of
asymmetric screened rooms for electromagnetic
measurements'. Proceedings of IEEE symposium on
EMC, 1990, pp. 114-118
EMC TEST REGIMES AND FACILITIES
13 LAHITA, M.J.: 'RF shielded enclosure purchasing
considerations'. Interference Technology Engineer's
Master, 1988, pp. 37 and 386
14 SALATI, B.D. and CHAPMAN, C.J.: 'Maintenance
of aged modular shielded enclosures'. Interference
Technology Engineer's Master, 1988, pp. 38-388
15 BUCELLA, T. and SANCHEZ, G.: 'A low-cost
RFI susceptibility testing system'. Proceedings of
IEEE symposium on EMC, 1981, pp. 31-35
16 DAWSON, L. and MARVIN, A.C.: 'Alternative
methods of damping resonances in a screened room
in the frequency range 30 to 200 MHz'.
17 BAKKER, B.H. and PUES, H.F.: 'A novel
technique for damping site attenuation resonances
in shielded semianechoic rooms'. Proceedings of
IEEE symposium on EMC , 1990, pp. 119-124
18 LAWRENCE, B.F.: 'RF anechoic chamber test
facilities'. EMC Technol., April-June 1983, pp. 32-38
19 Indoor ground reflection EMC test range, System
86/3. Rayproof division of Keene Corp, Norwalk,
Connecticut 06856, USA
20 NICHOLSON, J.R.: 'Perform 'open field' measurements in a shielded enclosure'. 2nd symposium and
technical exhibition on EMC, Montreux, June
1977, pp. 413-418
21 'Ultra high performance flexible pyramidal
absorber'. Technical bulletin 8-2-2, 1-74, Emerson
& Cuming Inc.
22 'Thin-film absorber for 50 MHz-1 GHz'. Technical
bulletin 8-2-17, rev 6/75, Emerson & Cuming Inc.
23 KUESTER, E.F. and HOLLOWAY, C.L.:
'Improved low-frequency performance of pyramid
cone absorbers for application in semianechoic
chambers'. Proceedings of IEEE symposium on
EMC, 1989, pp. 394-399
24 GAVENDA, J.D.: 'Semianechoic chamber site
attenuation calculations'. Proceedings of IEEE
symposium on EMC, 1990, pp. 109-112
25 Eccosorb VHP RAM. Grace electronic materials
catalogue, p. 1-100. Emerson & Cuming (UK) Ltd,
838 Uxbridge Rd, Hayes, Middlesex, UB4 ORP, UK
26 MISHRA, S.R. and PAVLASEK, Z.T.J.F.: 'Design
criteria for cost-effective broadband absorber-lined
chambers for EMS measurements'. IEEE Trans.,
1982, EMC-24, (1), pp. 12-19
27 NICHOLS,
F.J.
and
HEMMING,
L.H.:
'Recommendations & design guides for the
selection and use of RF shielded anechoic chambers
in the 30-1000 MHz frequency range'. Proceedings
of IEEE symposium on EMC, 1981, pp. 457-464
28 TSALIIOVICH, A.: 'RF absorber qualification
criteria and measurement techniques'. Proceedings
of IEEE symposium on EMC, 1990, pp. 361-366
29 MENDEZ, H.A.: 'A new approach to electromagnetic
field strength measurements in shielded enclosures'.
Wescon record, Los Angeles, CA, Aug. 1986
30 LIU, B.H., CHANG, D.C. and MA, M.T.:
'Eigenmodes and the composite quality factor of a
reverberating chamber'. NBS tech. note 1066, Aug.
1983
31 CORONA, P.: 'Electromagnetic reverberating
enclosures: behaviour and applications', Alta Freq.,
1980,49, pp. 54-158
32 BEAN, J.L. and HALL, R.A.: 'Electromagnetic
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
177
susceptibility measurements using a mode-stirred
chamber'. Presented at IEEE symposium on EMC,
1978
MA, M.T. and KANDA, M.: 'Electromagnetic
compatibility and interference metrology'. NBS
technical note 1099 section 8
ROE, M.J.: 'An improved technological basis for
radiated susceptibility and emission specifications'. Presented at IEEE symposium on EMC,
1978
CRAWFORD, M.L. and KOEPKE, G.H.:
'Comparing EM susceptibility measurement results
between reverberation and anechoic chambers'.
Proceedings of IEEE symposium on EMC, 1985,
pp. 152--160
CRAWFORD, M.L. and LADBURY, M.J.:
'Mode-stirred chambers for measuring shielding
effectiveness of cables and connectors: An
assessment of MIL STD 1344A method 3008'.
Proceedings of IEEE symposium on EMC, 1988,
pp. 30-36
MA, M.T. and KANDA, M.: 'Electromagnetic
compatibility and interference metrology'. NBS
technical note 1099 section 2.22
DVORAK, T.J.: 'Fields at a radiation measuring
site'. Proceedings of IEEE symposium on EMC,
1988, pp. 87-93
MISHRA, S.R. and KASHYAP, S.: 'Structure of
EM field at an open-field site'. Proceedings of IEEE
symposium on EMC, 1988, pp. 94-98
FIZGERRELL, R.G.: 'Site attenuation'. Proceedings
of IEEE symposium on EMC, 1985, pp. 612-617
MADZY, T.M. and NORDBY, K.S.: 'IBM
Endicott EMI range'. Proceedings of IEEE
symposium on EMC, 1981, pp. 17-21
DeMARINIS, J.: 'Studies relating to the design of
open-field EMI test sites'. Proceedings of IEEE
symposium on EMC, 1987, pp. 115-126
DASH, G.: 'Computing equipment standards - An
update on cable and peripheral placement'.
Proceedings of IEEE symposium on EMC, 1987,
pp. 332-337
DASH, G. and STRAUS,!.: 'Studies on the use of
wood in open area test sites. Proceedings of IEEE
symposium on EMC, 1988, pp. 295-303
'Reference data for radio engineers'. (Howard W.
Sams, 1975, 6th edn.) pp. 4.28-4.31
MAEDA, A.: 'Note on EMI measurement at openfield test site (6): Effect of EU1-' shelter'.
Proceedings of IEEE symposium on EMC, 1990,
pp. 241-246
'Radio communication handbook' (RSGB, London,
5th edn.) p. 12.56
BENNETT, W.S.: 'Antenna to ground plane
mutual coupling measurements on open-field test
sites. Proceedings of IEEE symposium on EMC,
1988, pp. 277-283
BRENCH, C.E.: 'Antenna differences and their
influence on radiated emission measurements'.
Proceedings of IEEE symposium on EMC, 1990,
pp. 440-443
BENNETT, W.S.: 'Radiated EMI measurement
reproducibility'. Proceedings of IEEE symposium
onEMC, 1987, pp. 90-93
178
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
51 DeMARINIS, J.: 'The antenna cable as a source of
error in E1\1I measurements'. Proceedings of IEEE
symposium on EMC, 1988, pp. 9-14
52 T'KEYA, S. and MAEDA, A.: 'Note on EMI
measurement at open-field test site'. Proceedings of
IEEE symposium on EMC, 1985, pp. 593-599
53 CARTER, N.J.: 'The application of low-level swept
RF illumination as a technique to aid aircraft EMC
clearance'. Interference Technology Engineers
Master, 1990, pp. 236-252
54 PANKHURST, R.V.: 'The coupling of electromagnetic interference into aircraft systems'. Proceedings
of IERE conference on EMC, 1980, pp. 117-128
55 CARTER, N.J., REDMAN, M. and WILLIS, P.:
'Validation of new aircraft clearance procedures'.
Proceedings of IEEE symposium on EMC, 1988,
pp.117-124
56 AUDONE, B., FERRERO, G., GIORCELLI, L.
and VECCHI, G.: 'Critical examination of bulk
current injection techniques: Theoretical aspects'.
Proceedings of IEEE symposium on EMC, 1988,
pp. 109-115
57 OBERTO, G., BOLLA, L., ROSTAGNO, G. and
58
59
60
61
62
BARARDO, R.: 'Critical examination of bulk
current
injection
techniques:
Experimental
comparison'. Proceedings of IEEE sympoSiUll1 on
EMC, 1988, pp. 101-107
KERSHAW,
D.P.
and
WEBSTER,
M.J.:
'Evaluation of bulk current injection technique'.
Presented at IEEE symposium on EMC, 1990, (late
submission)
NEWTON, P.M.: 'Aircraft testing in the electromagnetic environment'. Proceedings of ERA
seminar on DEF STAN 59-41, December 1990,
ERA Technology, Leatherhead, Surrey, UK
BURBIDGE, R.F., EDWARDS, D.J., RAILTON,
C.J. and WILLIAMS, D.J.: 'Aspects of bulk
current immunity test'. Proceedings of IEEE
symposium on EMC, 1990, pp. 162-168
LEVER, P.H.: 'Development of a system level
bench
test
for
the
automotive
industry'.
Proceedings of IEEE symposium on EMC, 1990,
pp. 270-275
MARSHALL, P.C.: 'Convenient current injection
immunity testing'. Proceedings of IEEE symposium
on EMC, 1990, pp. 173-176
Chapter 10
ElectroDlagnetic transient testing
10.1 Introduction
The first two have been covered as part of the
continuous interference tests, as they have
developed alongside traditional EMC testing and
are considered together with continuous interference, often in the same standards. The remaining
three areas are dealt with in this chapter.
10.1.1 Transient types
Over the last 20 years traditional EMC testing has
concen tra ted on radiated and conducted emission
and susceptibility testing. This is carried out by
examining or generating signals as a function of
frequency, and this activity is sometimes referred
to as operating in the frequency domain. Some
discontinuous signal tests have also been carried
out as part of EMC work with specifications such
as MIL STD 461. These spike tests simulate
switching transients which may be induced onto
power lines when a neighbouring unit is operated.
Other additional power-line surge and drop-out
tests have also grown in importance over the years.
Now that EMC design is becoming a sophisticated and integrated part of electronic design, one
sees that the effects of both continuous interference and transient effects are having to be
designed out at the same time, and usually by the
same design team, as solutions for one type of
interference may compromise those for another.
Cost-effective protection across the whole field of
RF interference demands that a coherent set of
design techniques are employed to combat both
continuous and transient interference with the
minimum component count and cost.
In some cases, the solutions to transient
problems using nonlinear voltage clipping devices,
such as zener diodes or spark gaps, are not used
at all in controlling continuous interference.
However, to be effective their location in the
circuit and their position on the circuit board can
be crucial, but this may compromise the optimum
design for reducing continuous interference. The
designer must be able to produce a design which
is the best cost-effective compromise solution for
all the con tin uous and transient req uiremen ts
called up in the range of standards which the
product must meet.
For transient signals these standards can include
consideration of:
10.1.2 Continuous and transient signals
Before discussing these topics in detail it is relevant
to point out some key differences between the
conventional continuous interference EMC testing
and that required to demonstrate compliance
with 'transient' specifications. There are two
aspects which .are different:
The instrumentation is different
The conceptual models needed to best
understand the types of signals are different.
The instrumentation used for continuous and
transient measurement is different because it is
required to capture and present signal data in
different ways. Spectrum analysers or scanning
EMI receivers are needed to look at the
continuous interference as a function of frequency
[1]. The limits for conducted and radiated interference (and susceptibility) are all drawn on
frequency plots. Therefore all the instruments are
designed to produce data in that form. These
instruments generally do not preserve and present
phase data on the signals being measured, only
amplitude is recorded after being measured with
a given IF jvideo bandwidth and filter shape.
Measurement of fast transients cannot be made
sensibly using scanning receivers. Fast oscilloscopes or digital transient recorders must be used
to capture the waveform [2]. Certain aspects of
the waveform such as amplitude, risetime, PRF,
etc., are then con1pared with the limits set out in
the applicable specification. Most transient tests
are susceptibility tests and the instrumentation is
primarily used to confirm the waveform being
injected into the EDT while it is monitored for
any malfunction.
Test engineers and equipment designers will
find that when dealing with both continuous and
transient phenomena it is vitally important to be
able to hold two conceptual models in their minds
and to be able to switch easily between them.
Power-line spikes
Power-line surges and drop ou ts
ESD -- electrostatic discharge
NEMP - nuclear electromagnetic pulse
Ligh tning strike
179
180
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
These are the frequency domain concept and the
time domain concept.
The frequency domain is useful for representing
the spectra of continuous signals. The form of the
spectrum is fixed (within the observation time) and
does not change or evolve with time. A spectrum
can be considered to have two components,
amplitude and phase, see Figure 10.1. All the
details of the signal can be recorded if both the
amplitude and phase data are measured, but it is
usual in EMC testing, when using a spectrum
analyser or EMI receiver, to measure only the
am pli tude of the signal as a function of freq uency.
This results in some limita tions with regard to
spectrum manipulation (as will be seen) and it is
not usually possible to unambiguously reconstruct
AMPLITUDE PLOT
~
The magnitude trace is the only one
produced by a scanning spectrum
analyser.
All phase data is lost using such a
device
30
w
o
::::>.-.
I-~
8
Z
OC/)
20
«~
~e
:E :t:
:::)-e
10
a:~
t;
w
0CIJ
0
-10 ............._ ......._ .......-...._......_ .............- ...
o 10 20 30 40 50 60 70 80
FREQUENCY MHz
PHASE PLOT
+1t
W
...J
o
Z
«
w
~
s:
0
::E
::::>
a:
t;
w
0-
W
-1t
o
Figure 10.1
10
20 30 40 50 60
FREQUENCY MHz
70 80
Example of signal spectrum showing both
magnitude and phase components
the signal waveform with only the am pli tude of the
spectrum. Thus conversion from the frequency
domain (spectrum) to the time domain (waveform)
is unfortunately normally barred.
The time domain contains only a record of
signal amplitude as a function of time with
respect to a time zero, as would be seen on an
oscilloscope screen. It displays no frequency data
about the signal directly but a time-domain
record can yield this information by the
application of the Fourier transform [3-5J.
10.2 Fourier transforIlls
10.2.1 Introduction
The Fourier transform technique was developed
by].B.]. Fourier (1768-1830) to assist in solving
problems in heat conduction [4 J, but is so
powerful that it has become very widely used by
physicists and engineers and can be applied to a
whole range of problems. In the present sphere of
interest it is the means by which one can
transpose data between the frequency and time
domains. This will allow EMC designers and test
engineers to view information contained in a
signal from the point of view of both domains and
thus achieve maximum understanding of it. The
examination of prominent ampli tude peaks in a
spectrum and their comparison with dominant
waveform features can lead to an insight into the
type of circuits which are generating the interference signal. This is particularly useful when
carrying ou t design or diagnostic EM C testing.
10.2.2 The transform
Fourier series, Fourier transforms, Laplace
transforms and convolution theory are all linked
mathematical ideas which shed light on the relationship between the frequency and time
domains. The subject is wide and detailed, with
whole texts such as that by Bracewell [3J devoted
to its explanation. Clearly, in this chapter there is
no space to do other than give some of the
concepts involved and ·to state the formulas which
apply. Understanding Fourier transforms is so
important to being able to understand both
frequency and time-domain data that the reader
is urged to undertake additional study by
recourse to the References.
The central idea behind the Fourier series!
transform is that within linear systems a complex
periodic signal or response can be constructed by
the superposition of a number of simple harmonic
functions. This is illustrated in Figure 10.2 where
a complex signal is presented in the time domain
ELECTROMAGNETIC TRANSIENT TESTING
AMPLITUDE OF
WAVEFORM COMPONENTS
181
f--=-;T--·I
r1'-l'
FREQUENCY
I
o
"SPECTRUM"
OF INDIVIDUAL
FREQUENCY
~COMPONENTS
WAVEFORM
BEING ANALYSED
~DOMAIN ~
TIME---""
FREQUENCY DOMAIN
OBSERVATION
11ME
OBSERVATION
Figure 10.2
Relationship between time and frequency
domains
(1), all the simple harmonic components required
to synthesise the complex shape are laid out in
freq uency order (2) and the spectrum is then
simply the view along the frequency axis (3).
Consider the example of a complex apparently
discontinuous signal such as a square wave. It can
be constructed by the linear superposition of a
DC term and a large number of harmonically
related cosine/sine waves as shown in Figure 10.3
together with the general expression for the
Fourier series. A pictorial representation of the
Fourier series for a pulsed waveform is shown in
Figure 10.4 with each line representing a
component in the series. The first few lines of the
pulsed
waveform
spectrum
can
be
seen
represen ted in the frequency domain (3) in Figure
10.5. The individual cosine waves which make up
the complex time-domain waveform are shown in
(2). They are depicted as all having the same
phase with regard to the starting point on the
time axis. I t is therefore dictated that
Spectral lines
w
:::>
o
I-
:J
a..
~
<C
I
2
T
Figure 10.4
Reproduced by permission
or Hewlett-Packard
INDIVIDUAL COSINE
WAVES
"
LAn cos nwt
where f (t) represents the waveform in (1) and An
are the amplitude coefficients, n the harmonic
number, and w the angular frequency.
Frequency domain view
(Spectrum analyser)
Figure 10.5
1(0) ".
f(f) =
00
+ :I: an cos n 0) f + :I: bn sin nO)f
n=1
n=1
~
1
::J
~EQUE~CY
10.1
n=O
Sum of Fundamental,
Fundamental
2nd Harmonic
Average value
and average value
of wave
2nd Harmonic
/
3
"
00
f(t)
7'
FREQUENCYf
Rectangular pulse and Fourier series spectrum
Prequency and time domains (cosine waves
only)
10.2.3 Introducing phase
Unfortunately, this expression does not allow us to
compute the time domain waveform from a
knowledge of the amplitude and frequency of the
lines in the Fourier spectrum as shown in Figure
10.5(3), because it is assumed that all the simple
harmonic components are cosines with the same
phases. In general, the phases will not be the
same and so an extra term is introd uced:
00
Figure 10.3
The Fourier series: building up a pulse
Reproduced by permission or Hewlett Packard
J(t)
LAn cos (nwt+cPn)
n=O
10.2
182
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
where c/Jn is the phase of the nth component.
But
cos (OJt
+ c/J) == cos c/J . cos OJt -
sin c/J . sin OJt
in which cos c/J and sin c/J are constants that can be
represented by a and b:
cos (n OJ t + c/J n)
== an
Incorrect - arbitrary waveform.
(No phase data)
ARBITRARY
7
w
The Fourier transform pair is expressed usually in
one of three ways [3J and is given here as stated
in Reference 8:
F(w)
=
J~ooj(t) e-iWldt
(direct transform)
cos n w t - bn sin n w t
and this result leads directly to the expression for
the Fourier series given in Figure 10.3.
If only the amplitude of the cosine and sine
terms are known (as measured by a spectrum
analyser) this is equivalent to losing the phase
information which is required to synthesise the
time-domain function f(t) and it cannot be
determined unambiguously. By assigning different
val ues of phase to the spectral lines in view (3) of
Figure 10.5 a range of arbitrary waveforms can
be produced in addition to the correct waveform,
but all of which have the same amplitude
spectrum, as illustrated in Figure 10.6.
Cl
10.2.4 Fourier transform expressions
10.3
and
f(t)
== -1
2n
Joo
.
F(w) elwtdOJ (indirect transform)
-00
10.4
wheref(t) is the time varying function and F(OJ) is
the frequency spectrum. A good library of
waveforms and Fourier transforms is available [8J
which can aid the EMC engineer in analysing
spectra or predicting the spectrum of a given
waveform.
Present-day firmware embodiments of the
Fourier transform are very fast and can produce a
1024-point FFT in a fraction of a second. While
the manufacturers take care to prevent signal
aliasing [2J and carefully select window options
such as Hanning and Hamming [2J in addition to
a simple rectangular 'boxcar' function, the expert
user of such advanced instruments will need to
have studied the effects of signal convolution [3J
with the measurement instrument time window to
be able to detect instrument/measurement artifacts.
::)
I-
~
~
"CORRECT"
~SES
FREQUENCY
~
AMPLITUDE SPECTRUM ONLY
(no phase data)
'Correct' waveform - reconstructed
using phase information.(Sine &
Cosine terms in the Fourier Series)
Figure 10.6
Reconstruction of the true waveform jrom
spectrum
This explanation has been made to illustrate how
powerful the technique of Fourier analysis can be in
transposing between the frequency and time
domain, and also to show that it is not possible to
make rigorous use of the transformation with only
amplitude data in a spectrum as generated by a
spectrum analyser or EMI meter. I t is possible
though to use the full power of the Fourier
transform when suitably digitised waveform data
are processed using digital fast Fourier transform
routines which are now firmware-based and self
contained within modern instruments [6, 7J.
10.2.5 Impulse response
Consider a simple network (a resonant filter)
shown in Figure 10.7. I ts performance is usually
determined by a scanning CW technique using a
vector network analyser (for amplitude and
phase) giving rise to the filter frequency response
as either amplitude and phase plots against
frequency or sometimes in the form of a Smith
chart.
The complementary time-domain technique is
to determine the filter impulse response by
subjecting the input port to a very fast step
func tion waveform with a rise time tmin' This
minimum rise time is equivalent to the maximum
freq uency which has been scanned in the
frequency domain method. The filter will respond
(ring in this case) in a characteristic way which is
observed from the waveform at the output port.
This waveform is called the impulse or step
response of the filter and contains time details
resolvable down to the limit set by tmin' The
impulse response and the frequency response are
related by the Fourier transform pair.
Now consider calculating the output from the
filter for a given input signal and proceed in two
ELECTROMAGNETIC TRANSIENT TESTING
SWEPT FREQUENCY
NETWORK ANALYSER SOURCE
NETWORK FREQUENCY RESPONSE
(AMPLITUDE & PHASE)
,,
PHASE
.....
Single frequency
scanned to Fmax
W
0
J~-"
~
::::>
t-
:J
Fmax
Q.
~
I
DC
183
~
FREQUENCY
::E
a:
INPUT
NETWORK
UNDER TEST
a:
,
,~
~
0
tl
III
OUTPUT
A TIME DOMAIN
MEASUREMENT
STEP OR IMPULSE
GENERATOR
::E
f2
A FREQUENCY DOMAIN
MEASUREMENT
a:
a:
~
~
NETWORK
IMPULSE RESPONSE
t
---SLOPE
IItm1n "
Fastest slope in response
is slower than IIt min
tmin is related to Fmax
Figure 10.7
ll
Network measurement infrequency and time domains
INPUT SIGNAL SPECTRUM
(phase not shown)
FREQUENCY RESPONSE OF NETWORK
(phase not shown)
w
w
w
Q
o
0
:::>
I-
:::J
c..
::E
«
I-
:::>
:::J
:::J
I-
c..
c..
:E
«
«
::J
::E
FREQUENCY
t
SPECTRUM OF OUTPUT SIGNAL
(phase not shown)
FREQUENCY
F1 (00)
x
F2 (00)
F3(OO)
(MULTIPLY)
~~
a::u..
:::JCf)
OZ
u..«
a::
I-
......
w
NETWORK IMPULSE RESPONSE
INPUT WAVEFORM
,
......
:::J
~ IL+-..........~~I-'-~...,.,....,__-
I-
c..
::E
w
w
o
0
:::>
:::J
OUTPUT WAVEFORM
TIME
c..
«
f2 (t)
f1 (1)
~ fI--t-+---1r----1"--':--+~+.:>Iitrc"...T,-IM-E
::E
::E
«
«
o
:::J
f3 (t)
(CONVOLVE)
Figure 10.8
Multiplication in frequency domain and convolution in time domain
complementary and connected ways, one in the
frequency and one in the time domain. Consider
the input signal defined by the frequency
spectrum F 1 (w) in Figure 10.8. This can be
multiplied by the network frequency response
F 2 (w) (linear amplitude) to yield the output
spectrunl F3 (w) in the usual way. If the ou tpu t
waveform is required, it can be calculated from
the output spectrum (amplitude and phase) by
the application of the Fourier transform.
184
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
narrow range of some variable. All measurements
of physical quantities are limited by the resolving
power of the instrument and convolution theory is
the underlying mathematical description of the
smearing process.
f (t)
10.2.7 Advantages of time-domain
manipulation
9 (t)
feu)
"
,"'.-g(t-u)
/w.
, ,,'
f(
u) g ( t-u)
u
F (t)
0fJ
....,
f f ( u ) 9 (t - u ) du
'
F (t)
10.9
......... -011
f(x) *g(x)
Convolution and manipulation of data in the time
domain is very irnportant if engineers and
designers are to be able to understand the significance of complex waveforms and their interaction
with electrical networks. This ability is useful in
considering for example the impact of a unidirectional NEMP step pulse shown in Figure 10.1 Oa
on a target system, and in relating it to the
ringing waveform which is specified for NEMP
current injection into a target EDT in MIL STD
462 CS10. See Figure 10.10b.
It should be clear that the situation is exactly that
described in Figure 10.8 where the excitation pulse is
modified by the impulse response of the target
Representation of convolution process
Reproduced by permisssion or McGraw-Hill
Approximately
- 50 kVIM
a:
10.2.6 Convolution
w
The output waveform can also be calculated
by convolving the input waveform with
the network impulse response. Convolution is a
mathematical process with wide application and
is described by Bracewell [3J. The convolution of
two
and g(t) is given by
tii
E (t) = A (e-at - e-pt)
~
/
~
o
>
"'V
J~oof(u)g(t -
u)du
10.5
and is written as f (t) *g (t). The process can be seen
by inspecting Figure 10.9 where two sample
functions of t are drawn out. For a given value of t
the function g(t u) is multiplied by f(u)and
integrated over u. The value produced is the value
of the convol u tion in tegral at that value of t and is
represented as a single value of F(t) by a line with
a heigh t proportional to the area under the
product curve. rThe output function F(t) is
evaluated by the above process for all values of t of
interest. rThis process is sometimes called the
composition product or the superposition integral
and at first sight it may seem difficult to evaluate,
but is amenable to solution by simple computer
numerical techniques. I t has wide application
beyond the filter example in Figure 10.8.
Convolution is useful in describing the action of an
observing instrument when it makes a weighted
mean measurement of some quantity over a
10 nanoseconds
TIME---............
(a)
IZ
W
0::
a::
::>
a. U
- .s
TIME
a.
(b)
Figure 10.10
Representation of an exoatmospheric
NEMP pulse (a) Double exponential
(b) US MIL STD 461 CS10 waveform
for injection into pins/cables on an EUT.
Ip == 1.05 Imaxe-nft/D sin (2nft) where
Ip == common mode pin current in amps,
f == frequency, Hz, t == time, s,
D
decay factor
ELECTROMAGNETIC TRANSIENT TESTING
system, leading to the ringing type waveforms that
are conducted along cables into the EUT. Riad [9]
compares the advantages to be gained by solving
transient problems in the time domain with those
offered using the frequency domain, and using both
in a hybrid fashion with Fourier transforms as a
connection. This is illustrated by rigorously
deriving the 'impulse response of a simple RC
network using each of the three approaches. He
points out that obtaining solutions to problems in
the time domain is not widely taught but offers
advantages which are self evident to those engineers
prepared to learn the techniques involved. The
main advantage of formulating problems in the
time domain is that nonlinearities can be properly
treated, as can systems which change with time.
10.3 ESD - electrostatic discharge
10.3.1 Introduction
Potentially damaging electrostatic discharge to
electronic components and equipment caused by
contact with human beings, tools and office
furnishings has been of concern since at least the
early 1970s [10]. The ESD problem can be
considered in two areas:
(i)
(ii)
ESD to vulnerable components such as
MOSFETs in manufacture, storage, handling,
transport and assembly into products.
ESD to finished products such as desktop
computers in the operational environment.
This is caused by the electrical charging of
humans and furniture etc. in dry airconditioned offices fitted with carpets and
chairs made from synthetic materials.
I t is estimated [10] that the cost of ESD damage in
the USA alone was around ten billion dollars a year
in 1988, and that this may increase as devices
become more sensitive with increasing scale of
integration. Control of ESD in the first category,
the production phase, is amenable to control
through the im plementa tion of careful procedures
and the use ofspecial antistatic bags and containers.
Four generations of antistatic materials have
been produced:
First generation
pink polythene
Developed in the 1970s it has a surface resistivity of
9
between 10 and 10 12 ohm per square, but it had
low stiffness, poor dimensional stability, short-lived
electrical properties and was easily damaged by
solvents.
Second generation
antistatic polypropylenes
This material owes its antistatic properties to
185
hygroscopic additives which draw in moisture
from the air. I t has the same resistivity as pink
poly but persists for longer; for about five years.
Third generation polypropylenes
conductive
This material has carbon black incorporated into
the resin and has a surface resistivity of 10 5 ohm
per square. The antistatic properties are
permanent and the substance has a higher rigidity
and dimensional stability than earlier materials.
Fourth generation materials
fibre impregnated
These materials are impregnated with a random
network of fibres that provide structural reinforcement and static charge dissipation. They offer
permanent antistatic properties, a high resistance
to sloughing and to chemical agents.
The second category of ESD problems, which
affects completed electronic products in the
operational environment, cannot be easily
controlled by procedure. Resistance to ESD must
be designed into the product by careful choice of
components, their positions on circuit boards, the
use of electrostatic and electromagnetic shields,
protection of circuits backing onto connector pins
by the use of fast switching limiters, the choice of
suitable materials for product cases and the
careful design of case joints, edges and apertures.
To design in ESD protection the designer must
understand the nature, magnitude and frequency
of occurrence of ESD events and how they are
generated in the operational environment.
10.3.2 The ESD event
Human beings can acquire electrostatic charge
when walking or shuming along a carpet by a
process known as the triboelectric effect. Two
dissimilar materials such as wool in the carpet
and rubber on the soles of shoes can exchange
charge which then builds up on the person. The
charged individual then moves towards a piece of
electronic equipment such as a personal computer
and discharges the stored energy to it via a finger
tip or a metal object such as a ring, pen or tool of
some kind. The resulting spark to the case
produces a fast risetime current which is injected
into the equipment and can disrupt or damage
the device.
Depending on the two materials and the rate at
which they are rubbed together, ch~rge will build
up at different rates on the two objects. The
affinity for materials absorbing charge can be
ranked in a table known as the triboelectric series,
186
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
Table 10.1
Positive
Negative
Sample common materials arranged in
triboelectric series
Air
Human hands
Asbestos
Rabbit fur
Glass
Mica
Human hair
Nylon
Wool
Fur
Lead
Silk
Aluminium
Paper
Cotton
Steel
Wood
Amber
Sealing wax
Hard rubber
Nickel, copper
Brass, silver
Gold, platinum
Sulphur
Acetate rayon
Polyester
Celluloid
OrIon
Polyurethane
Polyethylene
Polypropylene
PVC (vinyl)
KELF
Silicon
Teflon
16
15
14
13
>
~
w
(')
11
~
....J
10
>
9
0
w
8
0:
7
(')
~
J:
0
6
5
WOOL
4
/
3
2
1a--.--&...-.a..---a._01---+---a._..a.-.......a---a._.......
5 10 20 30 40 50 60 70 80 90100 RHO/o
Figure 10.11
Typical voltages to which humans will
charge as function of relative humidity.
Maximum values of electrostatic voltage
to which operators may be charged while
in contact with the materials shown
Reproduced by permission of BSI
circuit as shown in Figure 10.12 and has been
adopted by the lEG for lEG 801-2 and by the
DOD for MIL STD-M-385IO. ~1ore complex
models have been proposed to account for faster
risetimes of the leading edge of the pulse and to
produce multiple discharges, which are both
sometimes
observed
under
normal
office
conditions. A crude description of the worst-case
waveform and its frequency con ten t resulting from
the simple RC model discharge is given in Figure
!zw
and an extract from the US DOD- HDBK-263
(1980) is given in Table 10.1.
Once the charge begins to build up on a person
due to the triboelectric effect a second effect
begins to take place which bleeds off charge to the
surroundings. This discharging effect depends on
the humidity of the air: thus ESD problems can
occur more frequently in air conditioned offices
where the humidity is low. The voltage to which
a person becomes charged depends on the amount
of charge acquired and the self capacitance of the
individual. In general, the larger the surface area
of the body the larger is the self capacitance [11 J.
Jones [12J gives data for the voltages to which
humans can be charged when in contact with
various materials as a function of relative
humidity, see Figure 10.11.
The basic human ESD model IS a simple RC
12
A
Discharge model
~40A
,....., 500 ohms
----+~
,.....,200 pF
:::>
20 kV
o
w
*
"«
0::
J:
o
en
o
time
~
~
w
A
~20dB
o
/perdecade
-I
«
0::
t-
O
W
D-
en
10 MHz
~
200 MHz
10Hz
FREQUENCY
Figure 10.12
Typical assumed worst-case ESD
waveform
ELECTROMAGNETIC TRANSIENT TESTING
Probe tip inductance
- - Ground return
inductance
.... A
z
w
~ 40A
::::>
()
w
o
ex:
c(
:r:
()
(j)
B
time
Figure 10.13
Ground return inductance impairs desired
waveform
10.12 [11]. I t can be seen that the risetime is of the
order of 1 ns with a tail about 100 ns long.
In a portable ESD simulator test equipment
the achievable risetime is governed by the
inductance of the tip and ground return leads
shown in Figure 10.13. Risetime is im portan t
because it is known to affect the susceptibility of
an EDT to ESD of a given voltage. Thus
producing an ESD simulator with a required
and repeatable risetime is an important goal of
simulator design.
When the energy stored in the capacitor of the
simple RG model in Figure 10.12 is discharged
into a short circuit a current of up to 40 A can
flow into the EDT. In nature both positive and
negative polarities can build up on human skin.
However there is no clear evidence [11] that
testing with either polarity produces different
effects in electronic EDTs. Most simulators and
standards, such as lEG 801-2 (1984), specify only
positive voltages.
10.3.3 TypesofESD
There are a number of types ofESD which give rise
to different voltage and current pulses to which
victim devices or equipments may be exposed. The
variability and fineness of detail which can occur in
ESD pulses has been explored by King and
Reynolds [13], amongst others. They measured
many hundreds of discharge events for both direct
finger contact and conduction through small
187
metallic objects such as rings. Events with leading
edges rising as fast as 300 ps were observed, as were
multiple discharges at modest voltages of 3-4 kV
when metallic objects were in the discharge path.
Transition regions were observed at voltages of 68 kV between variable very fast risetime and high
current events to the more repeatable conventional
slower (> 1 ns) pulses.
In some tests [13], fast pulse peak currents of
170 A have been observed at discharge voltages of
4kV. It has been shown by experiment that the
variety of ESD pulses is considerable and
argument still continues about the need to
simulate this variability, particularly with regard
to the fast-pulse phenomena. Throughout the
investigations however it is clear that the worst
case events (high current and fast risetime) are
observed when the discharge to the EDT takes
place through a metallic object.
The multitude of ESD events that occur in the
operational environment can be simulated by
three types of model [14].
10.3.3.1 Human body model
People are the primary source of ESD events and
the normal, slow discharge phenomenon ( lO15 ns risetime), can be simulated by the RG
network as sho~:t;l in Figure 10.12. The lEe 8012 (1984) standard calls for alSO pF capacitance
and the specified simulator circuit is given in
Figure 10.14.
CAPACITOR CHARGING
RESISTOR
"'" Rch
100Mn
16.5 k V Cs
CAPACITOR DISCHARGING
RESISTOR
\
Rd
150 n
150 PF
DISCHARGE
ELECTRODE
FUNCTIONAL
EARTH
Figure 10.14
ESD probe circuit from first edition of
lEG 801-2
Reproduced by permission of BSI
10.3.3.2 Charged device model
Device leads, frames and packages can be
charged triboelectrically, just the same as
humans and can be discharged from the surface
of the device to ground via the pins or other
conductive parts of the device under test. The
charge vol tage and discharge energy will depend
on the position and orientation of the charged
device with respect to ground. In general the
ESD pulse produced with the charged 'device
model has a much faster risetime than that for
188
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
the human body model and can be substantially
less than 1 ns [14J. Bhar [14J conducted a
literature survey which showed that devices such
as a 64 K DRAM have an ESD damage
threshold of 2 kV when tested using a simulator
based on the human body model, but which
dropped to only 850 V when testing with the
faster pulse produced by the charged device
model. I t was observed that generally hurnanbody ESD caused junction damage to the device
whereas charged device ESD causes dielectric
breakdown [15, 16J.
10.3.3.3 Field-induced model
This simulates the effect of charge separation and
subsequent discharge on a device when it is
exposed to an external static electric field. The
mechanism of charge separation and subsequent
ESD on an integrated circuit placed in a field
generated by a potential gradient between the
charged object (not the IC in question) and the
ground is described by Unger [1 7J. The field
induced ESD model may be visualised as shown
in Figure 10.15 with the device lying in the
~+~
+
+
CHARGED
OBJECT
l
_
&t~~jj+~
iii
----~~~I~~~~~~~~~;;--/ ++++++++++++++++++++++++
external electrostatic field of the charged object.
The discharge pulse is fast, rather like that for the
charged device model and parameters have been
validated by Enoch and Shaw [18, 19J.
10.3.4 ESD-induced latent defects
Experimental work has been carried out [20, 21 J
in exploring the effect of ESD which does not
modify or destroy the device at the time of
application, but does cause an operational failure
at a later time. This is called the latent defect
mechanism. The existence of such a mechanism is
of considerable concern as devices which may
have experienced ESD events will not have
detectable failures and may be incorporated into
equipments which then subsequently fail. This
leads to expensive field diagnostics and equipment
repair with the attendant poor reliability image
which the product may then acquire in the mind
of the users.
It has been reported that CMOS ICs fail in a
latent manner owing to gate oxide rupture [20].
Gate oxide shorts can change character with
normal use and sometimes partially recover, but
sometimes degrade and cause intermittent or
permanen t failure [21 J. There has been some
suggestion that latent ESD effects could be
beneficial to device operation [22J as discharge
pulses have a 'hardening' effect which reduced
subsequent sensitivity to ESD damage.
10.3.5 Types of ESD test
C
I
1
2
=r=cc
=r:::
I
ESD testing is conducted using two different
techniques which can be applied directly or
indirectly:
Cg
Air discharge method
Contact discharge method
direc t tes t
} indirect test
EQUIVALENT CIRCUIT
c1
}'igure 10.15
___
Induced ESD on electronic devices
Cj == Capacitance between charged object
(+) and IC) C2 == IC capacitance
between top and bottom surface
C3 == Capacitance between lower plate
and bottom surface
Co == C2 + C3 == IC capacitance to
g;ound) R t
Resistance oj the test circuit)
R d and Cd == Resistance and capacitance
oj the device
There was some controversy in the late 1980s
about which was the more suitable type of test,
some preferring the reality of an air discharge at
the expense of repeatability, while others felt that
a reliable contact test was more important for
testing mass-produced items such as computers,
even if it did not simulate all the phenomena
observed in operational situations. If the question
of the need to simulate the fast subnanosecond
prepulse is also considered, it is evident that ESD
testing was an area for lively technical debate,
which still continues to some extent even though
standards such as IEC 801-2 have been re-issued
in draft to reflect some of the technical concerns
which had been raised.
ELECTROMAGNETIC TRANSIENT TESTING
10.3.5.1 Air discharge test
This has been the standard test for a number of
years and relies on the discharge taking place in
the air between the tip of the simula tor probe and
the surface of the EUT as shown in Figure 10.16.
The design of the ESD simula tor circuit and
shape of probe tip, as defined for example in
IEC80 1-2 (1984) attempts to replicate the ESD
Figure 10.16 Hand-held air discharge testing
CIRCUIT DIAGRAM
Rd
Rch
100MQ
16.5 kV Cs
DISCHARGE
ELECTRODE
150 Q
150pF
....FUNCTIONAL
EARTH
----------11...-.
DETAIL OF PROBE TIP
___BODY OF GENERATOR
ep8
/
~.
1
50 ± 0.02
_
AIR DISCHARGES
DISCHARGE CURRENT WAVEFORM
I
~
~
a:
1-----.
0.9
::::>
()
189
event from the body finger model giving rise to
the slow pulse shown in Figure 10.1 7. This test is
widely used the world over, but the knowledge
gained during testing has led to the realisation
that it has some deficiencies [12]. These include
The test did not always simulate EDT failures
observed in operational use
The severity of the test varied with relative
humidity
Equipment could fail at low voltage levels, but
pass at higher ones.
The test procedures for discharging to objects near
the E UT were not well defined, yet this indirect
test is important for items with plastic cases and
Iittle RF shielding.
I t had been shown [23] that the pulses produced
by air discharges were heavily dependent on the
rate and direction of approach of the simulator tip
to the EUT. Further, complex corona discharge
phenomena have been observed [24] which lead to
a reduction of the actual probe tip voltage from
the expected value by as much as 10kV /s for
corona current of 1 f.1A. Thus during the approach
time of the probe to the E UT the voltage could fall
from say 20 to around 10kV resulting in an
undertest. There are advanced air discharge
simulators which compensate for this effect by
internal tip voltage feedback circuitry [24].
Despite some of these problems· the air discharge
method is reported [25J as being specified by the
following standards in addition to the original
IEC801-2:
EIA PN 1361: The Electronic Industries
Association (USA) produced a draft standard in
1981 which focused on voice telephone terminals
req uiring body finger and body metallic models
to be simulated
ECSA: Exchange Carriers Standards Association
(USA) adopted IEC801-2 with regard to central
office telecommunications equipment in 1984 and
requires both direct and indirect discharge tests
NEMA DC33: National Electrical Manufacturers'
Association (USA) issued a draft standard in 1982
which focused on residential equipment and
appliances. It was never formally released but
called for both direct and indirect air discharges.
UJ
~
«
0.5 ....- . . . . . - + - -
10.3.5.2 Contact discharge test
I
()
C/)
is
0.1
Figure 10.17
ESD probe first edition of IEC801-2
(1984)
Reprod uced by permission of BS I
To overcome some of the unpredictable aspects of
the air discharge test, workers [12] have proposed
the introduction of a contact discharge simulator
where the EHT is switched to the probe tip
(which is held in contact with the EUT surface)
via a suitable closing switch. A circuit diagram of
the con tact discharge tester as specified in the
190
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
CIRCUIT DIAGRAM OF NEW GENERATOR
Tip is in contact with EUT SUrl~
_
---I===J------,r----e==t---+~ -Iof---''I/. FACE
II
OFEUT
D~~~~~GE
DISCHARGE RETURN
CONNECTION
DISCHARGE TIP OF NEW GENERATOR
-f-7~~~:
SHARP POINT
FOR CONTACT DISCHARGES
NEW DISCHARGE WAVEFORM
CURRENT I
I peak: 100%
90%
-
I at 30 ns
I at 60 ns .... - .....,..--
10%
very fast
risetime ---
Figure 10.18
fr
60ns
time
Details oj new IEC801-2 ESD test
Reproduced by permission oCBSI
second version of IEC80 1-2 is shown in Figure
10.18.
The most appropriate reliable fast risetime
switch was found to be a vacuum relay. The
probe tip is now pointed rather than rounded to
enable contact to be made through paint to the
metal surface of the E UT. The revised specification also stipulates a more complex waveform
which has a fast event before the main discharge
which can be seen in Figure 10.18. I t has been
reported [25] that the fast-edge events occur
under operational conditions only 3-5 % of the
number of actual events. However, Wood [26J
suggests that although the .fast spike may be
infrequent and contains little energy it is 'largely
responsible for voltage failures and the corruption
of IT equipment'. The slow pulse which follows
the spike contains most of the energy and is
considered to cause current failures and lead to
component damage.
In addition to the second version of IEC80 1-2, a
number of other standards call for a contact
discharge test and some also permit air discharges
where appropriate, as the contact method is not
suitable for injection onto the joints and seams in
the plastic case of an EUT.
ECMA
TR40:
The
European
Computer
Manufacturers' Association published a report in
1987 which changed the approach from air
discharge to contact discharge ESD testing. It still
permits air discharge tests onto plastics cases near to
conducting parts. The contact discharge test is also
permitted using a metal foil which is connected to
the close-by metal part/case.
ANSI: The American National Standards
Institute committee ASC C63.4 ScI began work
in 1985 to define a standard for testing products
and adopted the con tact discharge method
alongside the air discharge test. The method used
is at the discretion of the tester [25]. Both direct
and indirect tests are stipulated and the body
metallic and mobile furnishing models are used.
Draft 5 (1989) of the standard has been produced
and is directed to all electronic equipment.
SAE AIR 1499: The Society of Automotive
Engineers (USA) has produced several ESD specifications over the years, with this one being the
latest. It calls for either air discharge or contact
discharge and both body metallic and mobile
furnishing models are used. The SAE have also
made a proposal to ISO (International Standards
Organisation) calling for air discharge testing
using a body finger model to be applied to
automobile subsystems and components.
A more complete list of standards relating to
ESD can be found in Chapter 2 and Appendix 1.9.
10.3.5.3 Indirect ESD tests
In these tests either an air or contact discharge is
made to a conducting plane in the vicinity of the
EUT. This plane can be vertical or horizontal
and in several positions around the EUT; see
Figure 10.19. When the indirect discharge occurs
to the metallic plane the fast-varying currents
that are set up on the plane produce electromagnetic radiation which .couples to the EUT and is
deemed to be important in generating faults in it
[27]. The EUT is almost certainly in the near
field of the radiation for most of the frequencies
which make up the radiated pulse. Thus the
coupling to the EUT is very complex but involves
magnetic and electric induction fields and
radiative coupling. The repeatability of indirect
tests has been investigated [27J and it has been
found that there are three test parameters which
affect the outcome. These are
ELECTROMAGNETIC TRANSIENT TESTING
TYPICAL POSITION FOR DISCHARGE
TO VERTICAL GROUND PLANE ( VGP )
\.
191
approval' test it is important that no sensitive
areas are overlooked, otherwise there may be
problems in the field. I t is estimated that between
3,000 to 5,000 pulses need to be applied to a unit
such as a desktop computer to ensure all aspects
of ESD susceptibility have been covered. The
quality control verification testing can be carried
ou t wi th perhaps as few as 200 to 500 pulses.
10.3.7 ESD test voltage levels
Figure 10.19
Indirect ESD test for table-top equipment
Reproduced by permission of BSI
•
•
•
The location of the discharge on the flat plate;
discharging on the edges of the plate rather
than to the centre, makes a factor of two
difference in the voltage at which computer
E UTs are prone to fail.
The position of the simulator ground return
wire; this return wire appears to be a
significant radiator and its routing therefore
changes the field around the E UT. I ts effect is
to alter the disruption or failure threshold by
the equivalent of a few kV.
The location of the radiating plate ground
wire; this has been shown to have a small
effect on the disruption levels of an EU1-' and
is less significant than the two former ones.
10.3.6 Number of discharges per test
Jones [12J suggests in line with the revised
IEC80 1-2 that at least ten discharges (five
positive, five negative) should be applied to each
test point selected. Others [25J indicate that
many manufacturers/test houses use about 50
discharges per unit area. This may be defined as
the side of the case for example, or as discharges
per square metre. Other testers may use as many
as 10,000 pulses to test an EUT to make a valid
statistical analysis of its ESD withstand capability
[28J taking into account aspects such as EUT
cycle time.
I t is necessary to use more pulses to perform an
engineering characterisation of a product than to
perform quality control sampling. When the
engineering team carry out the ESD 'type
These will be contained in the applicable specification relating to the type of product being tested
and the country into which it is being sold. The
IEC80 1-2
ESD
standard is
widely
used
throughou t the world and the levels specified in
the new draft are given in Table 10.2. The
selection of a severity level for a test depends on
the type of materials and environmental
conditions that are to be found surrounding the
EUT in normal operational use. The IEC
recommended ESD levels are to be assessed from
Table 10.3.
The four severity levels from the lEe 801-2
(1984) standard are carried forward and a new
Table 10.2
IEC801-2 (second draft)
Test severity levels
Level
Test voltage
cantact discharge
Test voltage
air discharge
kV
kV
2
4
8
15
Special
1
2
2
4
6
8
Special
3
4
x(1)
Table 10.3
Selection of test severity levels (IEC801-21984)
ESD test voltage and environmental conditions
Class
Relative
humidity
as low as
Antistatic
Synthetic
%
1
2
35
10
3
50
4
10
Maximum
voltage
kV
2
x
x
x
x
4
8
15
Test severity levels are selected in accordance with the
most realistic installation and environmental conditions.
For other materials, for example, wood, concrete,
ceramic, vinyl and metal, the probable level is not
greater than class 2.
192
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
x-level in Table 10.2 is permitted, which can be
agreed between the manufacturer and user [12].
For air discharges, the levels remain the same in
the revised standard. However, because the
con tact discharge test has been shown to be
more s'evere at the higher voltage levels, the
voltages differ at the two highest levels. Contact
and air discharges are com pIe men tary, not
alternative, and should be applied as follows.
likely to grow rather than diminish, as experience
to date suggests that there may be other more
complex aspects to ESD discharges and their
interaction with equipments, which may be
revealed as oscilloscopes and waveform digi tisers
become faster and permit closer inspection of the
phenomenon.
10.4 Nuclear electromagnetic pulse
Contact discharges should be applied to areas
of the EDT which are accessible to an
operator in normal use and customer
maintenance.
Air discharges should be applied to case seams,
slots, air vents and keypads, etc. where the
discharge
could
penetrate
to
internal
conducting components and which cannot be
adequately tested in the contact discharge
mode.
10.3.8 Assessing EDT performance
Many readers involved with the electromagnetic
compatibility of commercial electronics may
have no direct need to understand the effect of
the radio freq uency pulse prod uced by a nuclear
weapon on their equipment. I t is suggested
however that this section con tains a good
example of a transient RF pulse and how it
interacts with equipment. Many of the general
points made earlier in the chapter about
convolution and equipment impulse response are
illustrated.
There are four categories of EDT performance
that need to be monitored during an ESD test:
10.4.1 Introduction
(i)
(ii)
(iii)
(iv)
Enrico Fermi suggested that electromagnetic
effects would be observed in the first nuclear
explosion in 1945 [29]. In 1954 Garwin at Los
Alamos estimated the parameters of the pulse that
would be radiated by an asymmetric gamma
source in the exponential growth phase of the
NEMP signal. In 1956 other workers in the USA
studied the possibility of using the EMP pulse
from a nuclear weapon to detonate magnetic
mines. The first serious attempt to understand the
impact of NEMP on possible target equipments
got underway with the Minuteman missile
programme in 1960.
The electromagnetic pulse is only one of a
number of effects produced by a nuclear
weapon. In order of promptness following the
detonation, the others are gamma, optical and
x-ray pulses, EMP, neutrons, thermal effects,
blast/overpressure, dust, debris and fallout.
Details of weapon effects are of course still
classified, but readers involved in this field are
Normal operation within specified limits
Temporary degradation/loss of function
which is self recoverable, known as
transien terrors
Temporary degradation/loss of function
which
req uires
opera tor
correction
(correctable errors) or system reset (non
correctable errors)
Degradation/loss of function which is not
recoverable due to component or software
damage, or loss of data, known as hard
errors.
The detailed statement of pass/fail criteria based
on the voltages at which the above performance
levels are recorded will normally be contained in
the test plan approved for the product in question.
Dash [11] suggests some acceptance criteria for
computer-like products, given in Table 10.4.
ESD testing is now accepted as an integral part
of the wider EMC testing field. I ts importance is
Table 10.4
Suggested tolerablepercentage errors for different test charge voltages
Test voltage
Transienterrors
Soft errors
Hard errors
Correctable
Non-correctable
DID
kV
DID
DID
5
10
15
20
0
50
100
100
0
5
15
100
0
0
DID
0
0
5
0.
100
0
ELECTROMAGNETIC TRANSIENT TESTING
referred to courses such as those run by RM CS
[30]. In this text it is intended only to acquaint
the reader with a broad view of issues relating to
the NEMP effect, methods of simulating it, and
basic test methods which are used alongside
those specified for EMC in documents such as
MIL STD 461BjC.
10.4.2 Types ofNEMP
The nuclear electromagnetic pulses to which
electronic equipments may be subjected are
produced by several mechanisms, of which the
gamma-ray mechanism is perhaps the most
important [29]. The EMP generation mechanism
and the resulting pulse depend on the height of
the weapon burst above the earth.
Surface burst: Occurs at an altitude of less than
2 km and produces an EM field similar to that of
lightning [31]. The prompt effects, however,
dominate at this range.
Air burst: Occurs at heights of 2-20 km and is
sometimes called an endoatmospheric detonation.
Both the prompt weapon effects and an EMP are
observed.
lligh-altitude EMP (HEMP): Sometimes referred
to as an exoatmospheric detonation which occurs
at heights in excess of 40 km and produces the
most general EMP effects over a large area.
For space-based electronic systems the prompt
radiation effects can produce an internally
generated EMP known as SGEMP (system
generated EMP) by direct interaction with
structure and components.
193
What follows concentrates on the exoatmospheric EMP effect because of its potential impact
on all types of civil and military electronic
equipment over a wide geographical area.
Rudrauf [32J reports that if a 1-5 megaton device
were detonated at an altitude of 300 km above the
Ba7J of Biscay the resulting EMP would contain
10 1 joules and would produce a pulsed field
strength of up to 50 kV jm over almost all of
Western Europe. Although the pulse would last
only a few hundred nano seconds the instan taneous
power would be some 500,000 million megawatts.
10.4.3 Exoatmospheric pulse generation
This has been widely described [29, 30, 32-34 J and
is treated very briefly here. The gamma pulse from
the detonation will build up with a risetime of a
few nanoseconds and propagate in all directions.
That portion of the flux travelling towards the
earth will interact with the upper layers of the
atmosphere as shown in Figure 10.20. The gamma
rays produce a flux of Compton recoil electrons
\,yhich constitute an electric current density with a
risetime of the same order as the gamma pulse.
The time-varying current density then gives rise to
the radiated EMP.
Each Compton electron receives about 1 MeV of
energy from the gamma interaction and can
produce about 30,000 electron ion pairs along its
track in the air. These secondary electrons make
no appreciable contribution to the EMP driving
curren t but they make for electrical cond uctivi ty
which limits the amplitude of the EMP and
influences the waveform [29].
Gamma ray energy
from explosion
Compton electrons deflected
by Earth's magnetic field
UPPERATMOSPHERE~ ~ ~I
DEPOSX~
~~
~
RADIATION REGION
:I
Figure 10.20
EARTH
Generation of nuclear exoatmospheric electromagnetic pulse
Gamma rays interact with neutral
particles in upper atmosphere to
produce energetic electrons by
"Compton II collision
Reproduced by permisssion of leT Inc.
194
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
12
.........
ill
~50
~ --~
- 100 kV 1m
10
:r:
IC)
Z
ill
«
I-
I-
a:
~
Cf)
z
o
ill
u:
8
W
..J
~10ns
~1MHz~50MHz 1GHz
TIME
FREQUENCY
(aj
Figure 10.21
(b)
NEMP exoatmospheric pulse (a) pulse
waveform (b) pulse spectrum
Reproduced by permission of' ICT Inc.
The waveform which propagates to the surface
of the earth is roughly represented by a double
exponential pulse [34 J of the type illustrated in
Figure 10.21, with a characteristic risetime and
falltime, and a peak amplitude of about 50 kVj
m. The spectrum can be obtained by Fourier
transform of the pulse waveform and is also
illustrated in Figure 10.21 showing that the
rnajority of the energy in the pulse is confined
to frequencies below a few MHz [30J. I t is
possible that in future new phenomena may
emerge which lead to pulses with enhanced
higher freq uency com ponen ts. Additional pulse
shapes and peak amplitudes derived from the
other types of NEMP generation are given by
Rickets et al. [33].
10.4.4 NEMP induced currents
The exoatmospheric pulse shown in Figure 10.21
can induce enormous currents into long wire
an tennas such as overground power lines and
represents a major threat to electrical generation,
distribution and control equipment. An estimate
of the induced current in such a power line is
given by Ghose [34J and shown in Figure 10.22.
Currents induced into the structures of systems
such as aircraft, missiles, radio towers and other
simple forms which can be represented by
electrical dipoles or monopoles with a reasonable
Q, (of around 5-10) are usually found to have the
characteristics of a damped sinusoid.
Results of the calculation of the induced opencircuit voltage and short-circuit current in an
example monopole [33J (7.5 m high and resonant
at 10 MHz) are shown in Figures 10.23a and b
and illustrate the general damped sinusoid
response. Other calculations and measurements
[35-37J have been made to explore the induced
currents in cylinders, wires inside leaky cylinders
and surface currents on other metallic bodies of
revolution. All indicate that the usual induced
current waveforms are bidirectional damped
0::
0::
::::>
0
0
6
0
::::>
0
~
4
w
2
0
0
2
4
3
5
6
TIME ( in micro seconds)
Figure 10.22
Example of currents induced into long
overhead power lines by exoatmospheric
NEMP
Reproduced by permission of' ICT Inc.
320------------.------
~
w
c:>
280
240
~
...J
200
o
> 160
'0 =10 MHz
l-
S 120
o
o0::
Z
w
c..
o
80
40
0 a...-_........_ _- ' - - _ - - - l l - - _........_ _....
0
100
200
300
400
500
TIME (ns)
(a)
~
2.0
1.6
zIw
1.2
ex::
0:
::::>
0
l-
0
U
0::
-0.4
Iex::
-0.8
0
I
C/J
= 10 MHz
0.4
S
0
'0
0.8
-1.2
0
100
200
300
TIME (ns)
400
500
(b)
Figure 10.23
Voltage and current induced into
7.5 m-Iong monopole e.g. antenna tower or
street lamp, by NE.MP stimulus
(50 k Vj m) (a) Open-circuit voltage for
7.5-m monopole (b) Short-circuit current
for 7.5-m monopole
Reproduced by permission of' Wiley
ELECTROMAGNETIC TRANSIENT TESTING
195
5...-------r-----r----,..---,-----,
I2
4
a::
a::
3
Oq>
2
W
:::>
20
1
52~
CfJ_
LL
il:
J
.......r__~
W
-4
::E
-5
w
t=
Measured
o
200
400
1000
a::
:::>
o
2
CfJ
E
1--
~ ~ 100
a::
a::
<
OJ
«
50
@
30
o
20 ........------------I"-----..JIL..-~..L-:-'~
1
10
20
5
~
}-'igure 10.24
FREQUENCY MHz
(bj
Examples of NEMP induction in aircraft
( aj Induced current waveform
( bj Induced current spectrum
sinusoids produced in response to the unidirectional NEMP incident pulse.
Damped-sinusoid induced-current responses
have been measured and calculated for complete
systems such as fighter aircraft [38, 39J and
missiles [40]. Figure 10.24a shows the induced
current density parallel to the fuselage of an FIll
aircraft, measured on the underside just in front
of the wings [38J. The plot is actually the time
derivative of the current density and needs to be
integrated over time to yield the actual current
waveform.
I t is common practice to record and present
time-derivative data as these are what is actually
measured by the special wideband Band D dot
sensors fitted to the EUT. The time derivative
exaggerates the higher frequency components in
the actual signal. If the necessary integration is
carried out at the sensor, problems of signal breakthrough, dynamic range and signal-to-noise ratio
may be encountered. The integration of the time
differential signal can be better carried out
digitally in the microprocessor of a digitising oscillo'scope at the recording site.
If the current density differential record given in
Figure 10.24a were integrated to yield the true
current density waveform, the fast variations
would be suppressed, but its damped oscillatory
10 MHz
----IIL-L.-
100 MHz
.....
10Hz
FREQUENCY
600
(aj
I-
52
PULSE SPECTRUM
LU
OF HPD SIMULATOR
ex:
10-2 ' - - (AFWLUSA)
---L.
1MHz
TIME (ns)
2
~
/
~
..J
-3
o
« 10-1
>
-2
<
~
LU
-1
~~
NOMINAL F-111AIRCRAFT
/FREQUENCYRESPONSE
a...
O~_I_-I-___f-""-~~r---~~
(J)
OW E
>-
>
w
o
:::>
.....
:J
Figure 10.25
NEMP simulator pulse spectrum and
frequency response of F111 aircraft
form would be preserved. The Fourier transform
of the true current density waveform is shown in
Figure 10.24b. This induced current density
spectrum shows a resonant peak at about 6 MHz
which corresponds to the main ringing in the
current waveform and is related to the electrical
length of the aircraft fuselage.
The tests on the F III were carried out by Kunz
and Lee [39J in the USA using a horizontal dipole
simulator
at
the
US
Airforce
Weapons
Laboratory, which attempts to simulate the
NEMP pulse. Its idealised frequency spectrum is
given in Figure 10.25. After recording many
measurements of the damped sinusoid type at
various locations on the aircraft a picture of its
main resonant properties could be built up and
the envelope of many spectra such as that in
Figure 10.24b was constructed, and is shown in
Figure 10.25. This inverted-V curve is an
example of the general coupling property of
systems with resonant, medium Q, metallic
structures and has been confirmed elsewhere [41 J.
All systems that have a frequency response of
this resonant form will have an impulse response
in the form of a damped oscillatory wave. This is
exemplified in Figure 10.26 which shows the
induced current in the skin of a missile [40J,
which is a high-Q, high-aspect-ratio metallic tube
and behaves like a fat electrical dipole. I t is
because so many real induced current waveforms
are damped oscillations that the current injection
NEMP tests called up in standards such as MIL
STD 462 CSI0/ll specify damped sinusoid
waveforms.
10.4.5 NEMP testing
NEMP testing can be divided into component,
equipment and system testing; each, type of test
requires different stimulation equipment and
different instrumentation. The order just given
reflects the complexity of the test and the cost
which can increase almost exponentially from a
196
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
incident pulse can be measured by instruments
which are either attached directly to the
component in a noninvasive way, or connected
external to the jig. The jig design may be based on
transmission-line techniques, the RF properties of
which are well understood, so that the pulse
waveform delivered to the component is not
distorted, and that the absorbed, reflected power
and component dynamic impedance can be
determined by measurement external to the jig.
Many types of active and passive components
have been measured over the years and a sound
database exists in various government and
industrial establishments. Component tests re
sometimes cond ucted with a simple sq uaretopped 1 IlS pulse [34] or a damped sinusoid.
Rickets [33] gives examples of upset levels for
active components and damage levels for active
and passive components in terms of watts for a
1 IlS pulse, see Figure 10.27. Much useful data on
in tegra ted circuit disruption and damage due to
RF energy are contained in a report by
McDonnell
Douglas
[42].
Figure
10.28,
rep rod uced from their report, shows the peak
power needed for burnout of a typical bipolar
opera tional amplifier integrated circuit as a
function of pulse duration. Figure 10.29 gives the
measured pulse energies [34] req uired to fail
various typical electronic components. Notice
that the most sensitive devices require less than
1 IlJ to destroy them.
.30
«
IZ
Resonant frequency is located where there is
--Llimited energy in NEMP spectrum (~30 MHz ),
.20
so induced current is low.
W
Ringing frequency is characteristic
/ O f object length
a:
~
u
.10
z
~
o
0
w
u
5
.10
~
.20
o
100
200
300
400
TIME! NANO SECONDS
Figure 10.26
Example of current induced in short object
such as missile by NEMP
Reproduced by permission of' BAe Dynamics Ltd.
few hundred pounds/dollars for a component test
to many millions for tests on large complex
systems such as an aircraft or ship.
10.4.5.1 Component testing
This is carried out by a direct injection method onto
the component terminals when mounted in a
suitable jig. The jig must accommodate the
component in such a way that the true RF power!
energy absorbed by the component from the
Figure 10.27 Thresholds for
typical active and passive
electronic components
WATTS
WATTS
100,000"""TRANSFORMERS
INDUCTORS
-106
10,000 'WIRE WOUND
RESISTORS
POWERSCRs
POWER DIODES.
HIGH POWER TRANSISTORS
ZENER DIODES
1-105
1-104
~
100
i-
PAPER / POLYESTER
CAPACITORS
MEDIUM POWER '-103
TRANSISTORS
J FETs
H. V. RECTIFIERS
2
LOW POWER TRANSISTORS '-10
SIGNAL DIODES
LOW POWER
SWITCHING DIODES --10
FILM RESISTORS
CERAMIC-MYLAR
CAPACITORS
10--
1.0""TANTALUM
CAPACITORS
TTL LOGIC
LINEAR ICs
MaS LOGIC -1
MICROWAVE MIXER DIODES -0.1
DAMAGE THRESHOLD WATTS (1Jl S PULSE)
Reproduced by permission of'Wiley
1,000
CARBON
RESISTORS
0.1--- LINEAR les
TTL LOGIC
DTL LOGIC
0.01-i-
0.001
-
MOS LOGIC
DISRUPTION THRESHOLD
WATTS (1Jl S PULSE)
ELECTROMAGNETIC TRANSIENT TESTING
100
(fJ
~
10
~
0:
W
~
oa..
~
l1i
a..
NO BURN OUT
0.1
0.01
0.001
. a . -_ _...I.-.._ _...&...-_ _- - ' - -_ _--4
0.01
0.1
1
10
100
PULSE DURATION mSEC
Figure 10.28
Estimate ofpeak power required to burn
out bipolar op. amp. Ie as function of
pulse duration.
Reproduced by permission of McDonnell Douglas
PULSE ENERGY Jl J
101
102
104
_ _ _ _ _ _ POINT CONTACT DIODES
- - BI POLAR OP. AMP. ICs
r-OW POWERTRANSISTORS--------HIGH POWER TRANSISTORS SWITCHING DIODES ZENER DIODES RECTIFIER DIODES - RELAY CONTACTS
----I
tw CARBON RESISTORS
Figure 10.29
-
Examples ofpulse energy required to
damage electronic components
Reproduced by permission of leT Inc.
Much has been written on designing equipment
to withstand NEMP attack and the data on
component hardness are important in this context.
Many protective measures can be taken [33, 34] to
reduce the ingress of pulse energy to that which
components can survive. These include screening
cables, shielding equipment, fitting transient
clipping devices and filters. The first real test of
many of these interconnected design features
occurs at the equipment or box level.
10.4.5.2 Equipment testing
Some equipments may be installed in the'final system
such that the only NEMP induced energy to which
they are subjected comes along cables or other
conducting pipes or hoses. In this case current
injection using damped sinusoids is the appropriate
technique. Other equipments may be exposed to
both current injection via cables and directly to the
NEMP wavefield. In this case both a damped
sinusoid current injection test and a radiated test
using a simulated NEMP pulse are both needed.
197
Specifications for NEMP testing usually only
apply
to
military
equipments,
but
the
requirement may be extended to cover certain
items of commercial electronics such as telephone
and telecommunications systems, power conditioning and distribution and computer systems. In
the UK, DEF STAN 00-35 describes all environments which are relevant to military equipments,
including natural ones such as lightning and also
includes a section on NEMP.
Design advice is available in DEF STAN 084
wi th regard to techniq ues for hardening
equipment against NEMP. Testing requirements
for equipments are exemplified in two technical
standards which are DEF STAN 59-41 in the UK
and MIL STD 461Cj462j463 in the USA.
Probably MIL STD 461 Cj462 represents the best
example of a set of NEMP related equipment tests
which are embodied within a wider framework of
general EMC testing. It is for this reason that the
NEMP tests called up in this standard are
examined more closely.
The structure of MIL STD 461 C is complicated
and different sections relate to tests on different
classes of equipment which are procured for use
by the Army, Navy and Air Force. It is not
intended here to define the exact applicability of
the various NEMP tests but rather to indicate the
types of tests a'fld their limitations when applied
to equipments. The NEMP-related tests in MIL
STD 461C consist of two types. The conducted
susceptibility tests CS 10 to CS 13 involve the
injection of damped-sinusoid waveforms into pins,
wires and cables. The radiated susceptibility test
RS05 requires equipment and interconnect cables
to be subjected to a unidirectional double
exponential simulation of the free-field weapon
pulse.
CS 10:
Conducted
susceptibility,
dampedsinusoidal transients, pins and terminals (pin
injection), 10 kHz-I00 MHz (MIL STD 462
notice 5 Navy).
CS 11:
Conducted
susceptibility,
dampedsinusoidal transients, cables, 10 kHz-l 00 MHz
(MIL STD 462 notice 5 Navy).
CSI2: Conducted susceptibility, common-mode
cable current pulse, interconnecting and power
(MIL STD 462 notice 6 USAF).
CS 13: Conducted susceptibility, single WIre
coupled pulse (MIL STD 462 notice 6 USAF).
RS05: Radiated susceptibility, electromagnetic
pulse field, transient (MIL STD 462 notice 5 Navy).
These NEMP equipment tests are described briefly
to illustrate a few of the more important test
requirements and instrumentation which should
be used.
198
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
ISOLATION
TRANSFORMER
TEST SAMPLE
_ _ _ _ LISNS
-
TEST INSTRUMENT or
TERMINATION BOX
\
ALTERNATIVE COMMON------MODE FILTER
~
DAMPED SINUSOID
GENERATOR
GROUND PLANE BENCH
DAMPED SINUSOID
GENERATOR
Figure 10.30
COUPLING DEVICE
~GROUNO
Figure 10.32
PLANE BENCH
Test configuration,lor US MIL STD
461 CS-10 NEMP pin injection test
CS 10: The test setup is shown in Figure 10.30. The
pin/terminal under test is accessed via a breakout
box using a short « 25 cm) low-resistance wire
and the damped-sinusoid current is indirectly
injected into it via an inductive (ringing
frequencies < 10 MHz) and capacitive (ringing
freq uencies > 10 MHz) probe. Alternative directcoupling techniques can be used with the
agreement of the EDT procurement authority.
l'he test waveform is that shown in Figure 10.1 Ob
and the value of the peak current at various
frequencies is taken from Figure 10.31. The test
should be conducted at frequencies of 0.01, 0.1, 1,
10, 30 and 100 MHz and at other EDT critical
frequencies. Ten pulses of both positive and
negative polarity should be injected at a rate of
between 1 per n1inute and 1 per second.
CS 11: The test configuration is shown in Figure
10.32 and the test waveform, maximum current,
test frequencies etc. are all similar to CS 1O. The
screens around cables which are to be tested are
(j)
100
a..
0.63 MHz
~
«
J-
z
x
«
~
...-I
10
\
CS10
CS11
/
::::> 0::
~::::>
X'O
«w
~Cl
~
z
o
~
~
oo
0.16
0.1
0,01 '--_ _--L.._ _---L
0.01
0.1
1
""--_ _- J
10
100
FREQUENCY ( MHz)
Figure 10.31
dealt with in different ways depending on the
nature of the cable. The specification should be
consulted for details. As with CS 10 the injection
signal genera tor is calibrated prior to use to set
the maximum test levels.
CS 12 and CS 13: The test configurations and
injected waveforms are similar to those for CS 10
and CS 11. The peak current as a function of
freq uency is shown in Figure 10.31. The pulses in
CS 12 are applied at the rate of 1 per second for a
period of 5 minutes, after which the polarity is
reversed and the test repeated. In the case of
CS 13 the pulses are applied at one pulse per
second for not less than 1 minute and a minimum
of 50 pulses must be applied for each polarity.
RS05: The EDT is set up in a 100 ohm parallelplate line as shown in Figure 10.33. The line
should have sufficient separation between the
plates such that the EDT occupies less than half
of the available height. The EDT shall have a
footprint which is smaller than the useable area
which has been previously mapped out during a
calibration exercise. The field strength as a
function of time is shown in Figure 10.21 and
simulates the standard exoatmospheric pulse. The
EDT is exposed to a minimum of ten pulses in
each of three orientations at pulse repetition rates
of between one per second and one per minute.
10.4.5.3 System testing
~~
o
MIL STD 461 CS-11 NEMP induced
cable current injection test setup
MIL STD 461 .NEMP current injection
limits
Testing large systems for hardness against NEMP
(or for EM C) is a difficult and expensive
undertaking. I t is only carried out on key systems
which must be shown to be able to survive the
high-level electromagnetic pulse. Such systems
might include long-range bomber aircraft, nuclear
armed missiles, fighter-bomber aircraft, ships,
command and control centres, mobile tactical
command and control facilities, telecolnmunications facilities, and key power generation and transmission facilities. There are two key interrelated
problems with testing systems such as these:
ELECTROMAGNETIC TRANSIENT TESTING
~~,.-_-_-_-_-_-_-_-_A_====::=::~--r
199
PARALLEL PLATE LINE
jlOn view)
/LOAD
TRANSIENT PULSE
GENERATOR
/
FRONT
I
'
-CABLE (in conduit)
SHIELDED ENCLOSURE
:---------,
USABLE TEST VOLUME
POWER LlNE-
TEST SAMPLE
INSTRUMENTATION
POWER
SOURCE
Figure 10.33
(i)
(ii)
Test setup for MIL STD 461 RS05 NEMP radiated susceptibility test
They are large 20-300 m (or greater) in extent.
Some systems such as communications centres
are fixed and must be tested in situ.
Simulating the correct NEMP waveform at
the high field strength required over such a
large target system. This calls for the
generation and precise shaping of a very
high-voltage pulse (up to 5 MV) that is
applied to the large radiating elements of
the simulator.
The technical and cost constraints which flow from
these two problems mean that it is not possible to
build a single, large all-purpose facility which can
test a whole inventory of systems. It has
transpired that individ ual simula tors have been
built to test specific types of systems. NEMP
simulators fall into two technical types:
(a)
(b)
Bounded-wave devices, where the energy is
constrained somewhat in the simulator
structure and, around the system under test.
Free-field simulators, where the wave is
generated and allowed to propagate freely
into free space. With such a simulator it is
possible to test a system such as an aircraft
in any orientation or even in flight (at
subthreat levels).
In general, the field strengths produced in the
bounded-wave devices can be at full threat level
(50 kV 1m), whereas the larger volumes covered by
free-field simula tors necessitate a reduction in
maximum field strength except close In to the
radiating elements.
10.4.5.4 Bounded-wave NEMP simulators
These may be of the following types:
•
Parallel transmission lines made from anum ber
of closely spaced wires with a tapered section
leading to the parallel-line working volume
and than via an opposite taper to a matched
load resistor. See Figure 10. 34a for a diagram
of the simulator referred to in MIL STD 462
RS05 for testing large systems. As an example,
Figure 10.34b shows a schematic of the ALECS
parallel-wire simulator (95 ohm line) at Air
Force Weapons Laboratory, Kirtland AFB,
USA, used for testing the B-1 bomber [34].
The working volume of this facility is
27 X 15 x 13 m cube. The peak voltage across
the line is about 1.7 MV, the peak E-field is up
to 125 kV 1m and it can fire one pulse per
minute. Another example of a parallel-line
simulator (125 ohm line) is ARES, which is a
Defense Nuclear Agency facility at Kirtland
AFB. It has a large working volume of
40 x 33 x 40 m cube and can produce field
strengths of up to 100 kV 1m [34].
In the UK, PETS 1 and 2 simulators at
AWE Aldermaston are parallel-wire lines and
like ALECS and ARES produce vertically
polarised waves. It is much simpler to build a
vertically polarised simulator than one which
200
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
SHIELDED ROOM
MARX GENERATOR
---+---~n.
TRANSMISSION LINE ANTENNA
WORKING VOLUME
(aj
----r-
- - - - - - - LOAD/TAPER
~L..-
95
~_ _--I---.-
25 m
/
12.75 m
-&--oh_m~
t E (t)
0
BANK PSU
VOLUME
PERFORATED
H (t)
METAL BASEPLATE
+
TOPV=--II~
MULTIPLE WIRES
i
(bj
Figure 10.34 Large system NE'MP test simulators
( aj Large parallel-wire line (b j USA
ALECS parallel-Loire NEMP simulator
(b) Reproduced by permission of leT Inc.
•
is horizontally polarised, as the lower
conductor can be laid on the ground for the
vertical simulator. However, the actual
NEMP from a weapon release may contain
predominantly horizontal polarisation and
this is more difficult to simulate with facilities
in close proximity to the ground. The
simulator and test target must be raised above
the ground by a significant fraction of a
wavelength at a few MHz if a horizontally
polarised pulse is not to be distorted by
interaction with the conductive ground. The
large TRESTLE simulator at AFWL,
Kirkland has two 5 MV pulsers producing a
horizon tal E- field from two vertical sets of
wires on a 61 x 61 m wooden platform which
is 36 m above the ground. 1'he cost of such
facilities is enormous, many millions of dollars,
but if NEMP hardening is to be proven at
system level, such simulators are necessary.
Tapered transmission lines, ,again constructed
from wires but with no parallel working
section. An example is shown in Figure 10.35a
of a line referred to in MIL STD 462 for
testing large systems to method RS05. A
drawing of a large 20 m high double-taper
simulator manufactured by Elgal EM-IIOI
ANT-II0 [43] is shown in Figure 10.35b. This
device can be equipped with a pulsed power
source of up to 2.5 MV for full threat
simulation. A facility called HEMP which is a
dou ble- ta pered line with the wires forming an
elongated diamond in plan view is located at
Fort Hauchuca in the USA. Each taper is 68 m
long and the intersection is 15 m high and 24 m
wide. I t can prod uce a field strength of around
26 kV 1m from a 400 kV pulser. In ,France,
Aerospatiale and Thomson CSF have
developed a large relocatable offset singletaper wire simulator for testing ground installations such as communications facilities [32].
I t can illuminate an area of 40 x 60 m with a
field strength of up to 50 kV 1m. A number of
other
bounded-wave
simulators
exist
including TEFS and SIEGE in the USA.
Details of these and other facilities exist in
published references [33, 34, 44, 45].
Simulators in France such as CYTHARE,
SIVA,
SIEM
2,
PEGASE
and
CORNE MUSE are listed by Rudrauf[32].
10.4.5.5 Free-field NEMP simulators
Simulators of this type have been constructed
mainly in the USA from horizontal dipoles,
resistively loaded dipoles and vertical conical
monopoles. The TEMPS (transportable EMP
simulator) is an example of a 300 m horizontal
dipole device. It can produce about 50 kV/m at
a distance of 50 m normal to the centre of the
dipole. Large horizontal dipoles have been
constructed similar to that shown in Figure
10.36. These simulators sometimes have a 15 MV switched pulser located at the centre of the
dipole, high above the system under test and can
provide near full threat pulses. Two 1000 ft longwire simulators have been built in the USA.
Such simulators with up to 100 kV pulsers can
radiate a field of about 1 kV 1m at 100 ft from the
antenna.
A vertical dipole facility formed from a
resistively loaded wire conical monopole above a
ground plane has been bu:ilt in the USA. It is
27 m high and is driven by a 4 MV pulser located
at the apex of the inverted cone, see Figure 10.37
a and b. Finally, one of the largest simulators has
been constructed on a floating barge for the
NEMP testing of complete ships. The EMPRESS
simulator in the USA is a vertically polarised
dipole using a large vvire monocone antenna as
shown in Figure 10.38.
There are regular symposia and conferences
[46] dealing with all aspects of high-voltage pulse
generators, NEMP and lightning with specialist
sections on simulators.
ELECTROMAGNETIC TRANSIENT TESTING
201
System under test
situated under the wires
(aj
~.
//~TANKS AND
OTHER VEHICLES
(bj
Figure 10.35
Large NEMP simulators (aj Double-taper NEMP simulator (bj Elgal ANT-110 double-taper
NEMP simulator
(b) Reprod uced by permission or Elgal
10.5 Lightning itnpulses
10.5.1 Lightning environment
Figure 10.36
Example of horizontal dipole NEMP
simulator
Reprod uced by permission or Eigal
The physics and electrical engineering associated
with the study of lightning and its impact on
electrical equipment is a distinct technical field,
with many workers contributing to the current
state of knowledge. In the space available here it
is only possible to introduce the reader to the
subject in ,the context of EMC testing electronic
equipment to withstand the large impulsive
electrical transients which lightning creates.
This natural electrical phenomenon has been
studied scientifically since Benjamin Franklin,
who remarked in 1752 that 'the clouds of a
thunder-gust are most commonly in a negative
state of electricity, but sometimes are in a positive
state'. The details of how the charge separation
202
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
phenomenon has continued, it has been necessary
to collect actual data on the nature of lightning
strokes and their frequency of occurrence around
the world such that protection against typical
strikes can be engineered into equipments. These
data have been analysed statistically to yield a
nominal description of the lightning discharge
event which has been used as the basis for a
number of standards and specifications. One such
is DEF STAN 00-35 which gives the standard
description of the discharge as:
/
CONICAL WIRE ANTENNA
( Z = 60 to 75
Q )
PULSER ( 1 - 7 MV )
(aj
WIRE
27m
-------39 m------
Figure 10.37
(bj
( a) Conical monopole above ground plane
(b) Vertical dipole NEMP simulator
Risetime
average risetime
== 2 J1S
value range
== 1-10 J1s
Duration
average duration
== 40 J1s
value range
== 20-200 J1S
Peak curren t
average value
== 20 kA
value range
== up to 150 kA
EM radiation
frequency of
maximum radiation == 10 kHz
Occurrence
storms worldwide at
any instant
== 2000
daily occurrence
== 5000
Other data .may be obtained from References 48
and 49.
(b) Reproduced by permission of I CT Inc.
10.5.2 Defining the discharge
mechanisms operate and the complex microstructure of lightning discharge formation are still
being studied and argued over [4 7J .
While the debate concerning the physics of the
Aerospace vehicles may experience different direct
discharges from ground equipment and this is
reflected in the standards which each type of
equipment must meet. Figure 10.39 shows the
standard double exponential form for the transient
Figure 10.38 7 MV
EMPRESS vertical
polarised 'dipole' VPD for
whole-ship testing.
Manufactured by Maxwell
Labs, USA
Reprod uced by permission or Maxwell Labs.
ELECTROMAGNETIC TRANSIENT TESTING
203
20""-----11
~
.-Z
....
Z
~ 10
a:
a:
.:¥.
w
ill
::::>
:::>
o
()
1< 5 X 10-3 sec
DURATION
Parameters of typical lightning pulse when
it strikes Earth
current pulse observed in a ground strike with
average risetimes and fall times and peak currents
suggested in DEF STAN 00-35, and cited by Keiser
[50J. A 2 J.1S risetime and 50 J.1S falltime doubleexponential pulse with a worst-case peak current of
200 kA has been specified in an early MIL-B-5087B
[51 J for aerospace systems and a pulse with similar
rate of rise of current (100 kAj J.1s) is suggested for
testing aerospace equipment by SAE [52].
The discharge in a natural lightning event has
been shown to be a complex phenomenon giving
rise to a number of components as shown in
Figure 10.40. The whole event may last for a
second or so and is commonly perceived as the
lightning flash. The testing waveform stipulated
TIME
not to scale)
0.25 sec < T < 1 sec
2 X 10-6 sec
Figure 10.39
I(
Figure 10.41 Lightning test waveform (SAE-AE4L).
A: initial stroke, peak
amplitude == 200 kA ± 10%; action
integral == 2 x 10 6 A 2 s ± 20%.
B: intermediate current, maximum charge
transfer == 10 coulombs, average
amplitude == 2 kA ± 10%. C): continuing
current, charge transfer == 200 coulombs
± 20 %, amplitude == 200 - 800 A.
D: restrike, peak amplitude == 100 kA
± 10%, action integral == 0.25 x 10 6 A 2 s
± 20 %, duration == < 500 /lS
200 kA
./
100 kA
\
«
~
IZ
W
7kA
/
a:
a:
::>
o
O
:
0
a
:
I
a
~
I
I
3.5 kA
400 A
~:
:
\
(}----·u
I
Q= 120C
IQ=5CI Q= 10C :
I Q=35C:
I
2J..ls 100J..ls 5ms
I
58ms
I
355ms
TIME (ms)
I
380ms
Q)
"0
Figure 10.42 Model of lightning strike waveform
showing peak current, duration and charge
c.>
en
~
,g
:eo
I-
Z
UJ
0:
0:
:::::>
()
TIME
FIRST RETURN STROKE
SUBSEQUENT
RETURN
STROKES
CONTINUING CURRENT
Figure 10.40
STEP-WISE
DART LEADER
Pictorial representation of the components
in lightning flash
Reproduced by permission of BAe Military Aircraft Ltd.
in the SAE AE 4L standard, and shown in Figure
10.41 encompasses the parameters of most
lightning strikes, and is divided into the four
components A to D.
Statistical studies of a great number of lightning
strikes have been carried out by NASA [53J
including both positive and negative discharges.
This has led to a model being defined which
accounts for 98%
of lightning strikes. The
idealised curren t profile is similar to that in the
SAE standard and is shown in Figure 10.42 [54].
It gives the current at various times during the
pulse along with the charge transferred during
these times. Details of current lightning standards
applicable to a range of equipments and situations
may be found by consulting
204
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
SAE Orange Book
CLM-R163
MIL STD 1757A
MIL STD 1795
FAA AC 20-53A
FAA AC 20-136
Do 160/ED14B (section 22)
MODAVPl18
There are reported to be a number of new
lightning standards under development (1991)
[55J which include
AC 20-53B
Do 160/ED 14C (sections 22 and 23)
EUROCAE:
Lightning test standard (WG31-SG3)
Lightning threat definition
Lightning zoning standard
10.5.3 Effects on equipment
Lightning can influence equipment in two ways.
The obvious means is by a direct strike where the
lightning channel attaches to the system at some
prominent point and leaves by some other point
to complete the discharge path to ground. Effects
may also be produced in nearby equipment
indirectly by electromagnetic fields radiated by
the rapidly changing voltages and currents in the
ligh tning channel.
The spectrum of a lightning pulse contains less
energy at HF and VHF than an NEMP pulse, as
can be seen in Figure 10.43. Most of the energy in
the lightning pulse is confined to VLF. Direct
strike and indirect effects can be considered
separately for two broad categories of equipment:
aerospace systems and ground equipments.
N
~
NEMP
E
LIGHTNING ( 2 / 40 lls )
~
Ci5
aJ
/ --7',
~10 kHz
CLARKE
o
~1MHz' /
60
Fast rising lightning
pulse (200 ns)
',.
,
(
PODGORSKI
62 )
COMMUNICATIONS
~
~
~
\
~
~
\
\
\
~
\
r--VLF
---+·1.. . . - - H F -----I,,~I-·-VHF -
conductors, magnetic forces leading to high
transient pressures, and fuel ignition. The indirect
effects include high transient magnetic field, upset
ground voltages across the aircraft, unwanted
operation of electrical power trips, and electromagnetic shock excitation of the aircraft structure
resulting in oscillatory currents.
This last topic is of particular concern in
connection with the assumed risetime of the
lightning stroke as it attaches to a prominent point
on the aircraft. Fast risetimes can occur during the
attachment/discharge. For shorter risetimes than
the normally specified 2 J1S (where 90% of the
energy is below 10kHz [60J), which have been
reported as being down to 200 ns [61 J, the
lightning pulse begins to have significant energy at
frequencies which can resonate with the aircraft
structure (5 to 20 MHz) and cause it to ring. This
produces a damped sinewave oscillation similar to
that generated by NEMP which can then couple
into cables and thus into avionics, which increasingly contain large quantities of sensitive digital
integrated circuits, and can lead to disruption of
function or component burnout. The indirect
effects of ligh tning on aircraft are covered in RAE
technical memorandum FS(F)457 which is
referred to by Carter [58].
Revised lightning specifications relating to aircraft
systems and avionics call for testing using a multiple
stroke waveform. There is one initial return stroke
with a peak current of 200 kA followed by as many
as 23 re-strikes of 50 kA distributed over a period of
up to 2 seconds with spacings between any two
pulses of 10 to 200 ms [59]. As with ESD measurements, it would seem that the exploration of the
actual physical events using faster detection and
recording equipment reveals faster risetime
phenomena,
which
have
previously
been
unobserved. The slower risetime oversimplified
models of ESD and lightning which have been used
to test equipments may explain some of the discrepancies which occur between the EUT performance
in the test laboratory and that actually experienced
in the operational environment.
FREQUENCY
Figure 10.43 Comparison oj RF spectra oj NEMP and
lightning pulses
10.5.3.1 Aerospace systems
Include civil and military aircraft, high altitude
missiles, and space systems transiting the
atmosphere. This is a major specialised field in its
own right [56-59J and is not pursued further here,
other than to point out some of the issues which are
of concern. The direct effects of a ligh ting strike on
an aircraft can include: arc burnthrough of high
resistance parts, acoustic shock, heating of
10.5.3.2 Ground equipment
Particularly power distribution and telephone
systems, radio communications and general
industrial, commercial and domestic electronic
equipment. Lightning effects on these equipments
are of more general interest to the majority of
designers and test engineers involved with EMC.
Consider the simplified situation shown in Figure
10.44 where lightning discharges are taking place
over an industrialised area with power and telecommunications systems feeding two interconnected equipments. These could, for example, be a
ELECTROMAGNET,IC TRANSIENT TESTING
POWER GENERATOR
- - V g _..··.....
/~L.v. P~ER L1NE~
LARGECURRENTS
GROUND VOLTAGE
FLOW INTO
DIFFERENTIAL DUE TO THE GROUND
HEAVY CURRENT FLOW
Figure 10.44
WI~
~
~
>
lime
SURGES, TRANSIENTS AND
DROPOUTS DUE TO VARIOUS
FORMS OF LIGHTNING STRIKE
Types of lightning discharges leading to
direct and induced effects on equipment
couple of desktop computers connected by a
modem link via a telephone line. Cloud-to-cloud
discharges result in a radiated electromagnetic
pulse which can couple into power cables and
result in a power line transient. A direct strike
from a cloud to the equipment is rare [60J and if
the building in which it is situated is protected
according to the advice contained in BS6651 the
likelihood of a direct strike is even more remote.
Discharges from cloud to ground that do not
strike an equipment directly are obviously more
common than those that do. They can produce
radiated electromagnetic field strengths of 6 kV 1m
at a distance of 1 km from the lightning channel
[62]. The measured spectrum of frequencies
produced by a typical discharge can be seen in
Figure 10.45 [63J. Note that this confirms that
lightning contains less high-frequency energy than
a NEMP transient.
The peak ligh tning channel current is limited by
the ground resistance in the particular geographical area where the strike occurs. In low
resistance coastal marsh areas the current may be
greater than 30 kA whereas in high-resistance areas
where the ground is predominantly granite the
10
r--.,...----r---r----r--------
N
J:
......
«
I:Z
10-1
205
curren t will be lower. The ground currents will
manifest themselves by developing large potentials,
Vg in Figure 10.44, between electrical grounds at
various places, and this will drive surges down the
power and communication return lines leading to
data corruption or damage to interface circuits.
Lightning is considered to be a significant cause
of power sags and transients. The peak transient
voltages can reach several kV [50J before arcing
through the insulation of commercial or domestic
power wiring at levels of around 10kV [60].
Gerke [64J asserts that 'in too many cases, power
disturbances
(to electronic equipment) are
overlooked or ignored by the manufacturer in the
hope that someone else
the user or the power
company
will solve the problem (of transient
failures of their equipment)'. However, not all the
power line transients or other effects are caused by
ligh tning. A resume of these other effects is also
given by Gerke and includes power sags, surges,
outages, harmonic distortion, frequency deviation,
superimposed transients and wideband noise.
10.6 Transients and general power
disturbances
10.6.1 Importance of power transients
All the disturbances previously mentioned can
sometimes occur on power lines as a result of local
loading or switching problems rather than from
external sources such as lightning. While the
undesirable properties of equipments generating
switch-off spikes and being susceptible to
incoming transients are addressed in military
standards, commercial equipment has in the past
had to operate in the presence of similar disturbances but without the comprehensive immunity
achieved by rigorous design in compliance with a
set of standards.
Early studies by IBM (1974) showed that most
power supply related problems with regard to
computer equipment were due to the existence of
transients on power cables. Other measurements
by AT&T and the US Navy have deduced that
vol tage sags and dropou ts were the primary
causes of computer disruption. Taken together,
this suggests that transient suppression and the
provision of internal stored energy in the
equipment are two necessary design features of
modern digital electronic equipment.
W
a::
a::
10-2
10.6.2 Examples of power supply
immunity standards
::>
0
10-3
1
10
100
1k
1Ok
100k
1M
FREQUENCY (Hertz)
Figure 10.45 Typical lightning spectral density
1OM
The CS06 spike test in MIL STD 461/2 has been
adopted as a good test for both military and
commercial equipment.
206
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
Examples of other relevant standards include
ANSI/IEEE STD C62.41 (1980) formerly IEEE
STD 587: Guide for surge voltages in low-voltage
AC power circuits, essentially a lightning damage
specification [64]. I t defines surge/transient
voltages and currents up to 6 kV and 3 kA. There
are two classes of equipment: Class A, those
connected further than 10m from the entrance of
the power cable into a building, and Class B,
those connected within 20 m of the power
entrance. Figure 10.46 shows the applicable
transient waveshapes and limits.
ANSI/IEEE STD 446 (1987): Recommended
practice for emergency and stand by power in the
USA. It gives recommended power limits for
computer systems as shown in Figure 10.47.
Notice that the transient am pli tude increases with
decreasing pulse width. Occasionally, levels can
reach 400 % of the line voltage for a 20 JiS long
transient.
ANSI/IEEE STD 519 (1981): 'A guide for
harmonic control and reactive compensation of
static power converters'.
IEC 801: Part 4 of international standard (which
applies to European equipments) concerned with
power transients, including those induced by
VOLTAGE
Vp
0.9VP
V peak
0.9V
p
0.5V u
0.1 Vp
(aj
TIME
TIME
60% of V peak
(bj
CURRENT
Ip
0.91 p
0.5Vp
'------
~~----;------.TIME
(c)
w
3000/0
C)
«
I...J
~ 200%
I-
Z
W
()
ffi 100%
0..
0%
'--_-'---_~----I_...&_
0.001 0.01
----I
0.1
1
10
100
TIME IN CYCLES ( 60 Hz )
~
1,000
Figure 10.47 Limits on transients and dropouts for power
supplies connected to computer systen1S.
ANSIIIEEE-STD 446-1987
recommended power limits
lightning. Part 5 deals with surges in electrical
power systems. Typical waveshapes are given in
Figure 10.48. This is probably the standard which
must be met by most new commercial electronic
equipment.
IEC 60-2: 'High-voltage test techniques' IEC 60-2,
gives a standardised 1.2/50 JiS lightning impulse
vol tage transien t and 8/20 JiS current surge pulse
similar to that for ANSI/IEEE C62.41 Cat.B [65J.
BS 5406 (1988)-EN6055: Concerned with disturbances to supply systems caused by household
apparatus and similar equipment. Part 2
Harmonics, Part 3 Voltage fluctuations.
BS 66~2 (1985): Guide to methods of measurement
of short-duration transients on low-voltage power
and signal lines.
BS 2914 (1979): Specification for surge diverters
for AC power circuits.
10.6.3 Summary
Figure 10.46 Examples of transient waveshapes on LV
power lines (ANSIIIEEE C62.411980)
( a) Category A and B voltage and current
( b) Category B only) voltage
( c) Category B only) current
Location
category
Waveform
Amplitude
A: Inside building
> 10 m from
entrance
(a) 0.5 ,us-lOO kHz
6kV
B: Inside building
< 20 m from
entrance
(b) 1.2 x 50,us
(c) 8 x 20 ,us
(a) 0.5 ,us-l00 kHz
6kV
3kA
6kV
500A
In this brief introduction to the nature of transients
and disturbance to power distribution systems it
has only been possible to acquaint the reader with
the broad categories of effects and show some
examples of applicable standards and specifications. With the fast growing implementation of
digi tal microprocessors in to industrial, commercial
and domestic equipment this area of electromagnetic compatibility is becoming very much more
important than it has been in the past.
Consequently, EMC design and test engineers
must be aware of this somewhat overlooked aspect
of electromagnetic interference engineering, and
not allow an otherwise compatible equipment to
be compromised by these conducted transients
and other power line phenomena.
ELECTROMAGNETIC TRANSIENT TESTING
V
UJ
C)
WAVE SHAPE OF A SINGLE PULSE
INTO A 50 n LOAD
1-+---~.....­
5
0.9-+-----.-
~
-J
o
6
~ 0.5+---4----4------.:JIIl~
CJ)
-J
:::>
0..
7
0.1
..t
_---'"
sons ±
""....
30%~
8
FAST TRANSIENT BURST
V
9
Repetition period (depends
on the test voltage level).
V
SINGL~ PULSE
-----/
IN BURST
I I 11 11I.li:
I I !il l
10
1
'1
~ 15 ms ~
(aj
'I,'
11
Burst duration
I
I
Burst period 300 ms - - - - - ,
V
§
1.0+----1W........
a ~ 0.9
9;«
Tr = 50j..lS ± 20%
T1 = 1.2j..ls ± 30%
Tf = 1.67 x T1
1
12
l IEC 60 - 2
13
at-
z-J
~
g 0.5
o
0.3
0.1
14
O~+-++-~-----------
t-
5
a
I
1.0+--:----r:-....
t- 0.9
~~
lr ~
ou
J:
1
Tr = 20j..lS ± 20%
T1 = 8j..ls ± 30%
Tf = 1.25 x T1
l
15
IEC 60 - 2
0.5+---4-+.,..-----~
16
CJ)
max. 30%
17
Typical transient burst and surge
waveforms (lEG 801) (aj lEG 801-4
transient burst (b j lEG 801-5 surge
waveform
Reproduced by permission of BSI
10.7 References
GLEDHILL, SJ.: 'Spectrum analysis' in BAILEY,
A.E. (Ed.): 'Microwave measurements'. (Peter
Peregrinus, 2nd edn., 1989) Chap. 13
2 'Digital signal processing'. Technical tutorial 1990
catalogue, LeCroy Ltd, 28 Blacklands Way,
Abingdon Business Park, OX14 1DY
3 BRACEWELL, R.N.: 'The Fourier transform and
its applications'. (McGraw-Hill, 2nd edn.)
4 CHIRGWIN, B.H. and PLUMPTON, C.: 'A
18
19
20
21
22
207
course of mathematics for engineers and scientists
volume 5'. (Pergamon)
FEYNMAN, R.P.: 'Lectures in physics'. (AddisonWesley) Vol. 1, Chapters 25, 47 and 50
7200 series digital oscilloscope 1990 catalogue.
LeCroy Ltd, 28 Blacklands Way, Abingdon
Business Park, OX14 1DY
TD230 1/TD 130 1 digitiser systems. 1990 product
catalogue. p. 162, Tektronix UK Ltd, Fourth
Avenue, Globe Park, Marlow, Bucks SL 7 1YD
'Spectrum analysis - pulsed RF'. Application note
150-2. Nov. 1972, Hewlett-Packard, Winnersh,
Wokingham, Berks, RG 11 5AR
RIAD, S.M.: 'Instructional opportunities offered by
the time domain measurement technology' . in
MILLER, E.K. (Ed.): 'Time domain measurements in electromagnetics'.
(Van Nostrand
Reinhold), Chapter 3, pp. 72-94
SCHAFFER, R.: 'Choosing an ESD container:
Materials and mechanics'. Interference Technology
Engineer's Master, 1988, pp. 122-128
DASH, G.R.: 'Designing to avoid static - ESD
testing of digital devices'. Interference Technology
Engineer's Master, 1985, pp. 96-110
JONES, B.: 'Improvements to the ESD testing of
equipment;. Presented at IEEE symposium on
EMC) 1990
KING, W.M. and REYNOLDS, D.: 'Personal electrostatic discharge: Impulse waveforms resulting
from ESD of humans directly and through small
hand-held metallic objects intervening in the
discharge path'. Proceedings of IEEE symposium
onEMC) 1981; pp. 577-590
BHAR, T.N.: 'Electrostatic discharge models
simulating ESD events'. Interference Technology
Engineer's Master, 1988, pp. 112-118
ENOCH, R.D., SHAW, R.N. and TAYLOR, R.G.:
'ESD sensitivity of NMOS LSI circuits and their
failure characteristics'. Proceedings of EOS
symposium on ESD) 1983
TAYLOR,
R.G.,
WOODHOUSE, J.
and
FEASEY, P.R.: 'A failure analysis, methodology for
revealing ESD damage to integrated circuits'.
Proceedings of EOS symposium on ESD) 1984
UNGER, B.A.: 'Electrostatic discharge failures of
semiconductor devices'. Proceedings of 19th international symposium on Reliability physics) 1981
ENOCH, R.D. and SHAW, R.N.: 'An experimental
evaluation of the field-induced ESD model'.
Proceedings of EOS symposium on ESD) 1984
SHAW, R.N. and ENOCH, R.D.: 'An experimental
investigation of ESD induced damage to integrated
circuits on printed circuit boards'. Proceedings of
EOS symposium on ESD, 1985
GAMMILL, P.E. and SODEN, J.M.: 'Latent
failures due to ESD in CMOS integrated circuits'.
Proceedings of EOS symposium on EMC) 1986
HAWKINS, C.F. and SODEN, M.J.: 'Electrical
characteristics and testing considerations for gate
oxide shorts in CMOS ICs'. Proceedings of IEEE
international conference on Test) 1985
CROCKETT, R.G.M., SMITH, J.G.
and
HUGHES, J.F.: 'ESD sensitivity and latency effects
of some HCMOS integrated circuits'. Proceedings
ofEOS symposium on ESD) 1984
208
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
23 DAOUT, B. and RYSER, H.: 'The correlation of
rising slope and speed of approach in ESD tests'.
Presented at 7th symposium on EMC, Zurich, 1987
24 RICHMAN, P., WElL, G. and BOXLEITNER,
W.: 'ESD simulator tip voltage at the instant of
test'. Proceedings of IEEE symposium on EMC,
1990, pp. 252-257
25 STAGGS, D.M. and PRATT, D.J.: 'Electrostaticdischarge standardization'. Proceedings of IEEE
symposium on EMC., 1988, pp. 175-178
26 WOOD, D.V.: 'Investigation of a new ESD test
method using current injection'. Proceedings of
IEEE symposium on EMC, 1988, pp. 179-185
27 MAAS, j.S. and PRATT, D.J.: 'A study of the
repeatability of electrostatic discharge simulators'.
Proceedings of IEEE symposium on EMC, 1990,
pp. 265-269
28 BUSH, D.R.: 'Statistical consideration of ESD
evaluations'. Proceedings of 7th international
symposium on EMC, Zurich, 1987, pp. 468-473
29 LONGMIRE, C.L.: 'On the electromagnetic pulse
produced by nuclear explosions'. IEEE Trans.
EMC-20, (1), 1978
30 Nuclear hardening course. Applied physics and
electro-optics group, Royal Military College of
Science, Shrivenham, Swindon, Wilts, SN6 8LA
31 KEISER, B.: 'Principles of electromagnetic compatibility'. (Artech House, 3rd edn.) Chap. 3, p. 48
32 RUDRAUF, A.: 'Electromagnetic pulse simulators
- EMP on tap'. Int. Def. Rev., 1984 (1)
33 RICKETS, L.W., BRIDGES, j.E. and MILETTA,
j.: 'EMP radiation and protective techniques'. (Wiley)
34 GHOSE, R.N.: 'EMP environment and system
hardness design'. Don White Consultants Inc.,
Gainesville, Virginia 22065, USA, 1984, 1st ed.
35 PAN, W.Y.: 'An experimental investigation of the
distribution of current and charge induced on a
tubular conducting cylinder by an electromagnetic
pulse'. IEEE Trans. EMC-27, (2) 1995
36 RODGER, K.S.: 'An approach to EMP testing a
complete aircraft'. Proceedings of IEEE symposium
onEA1C, 1977, pp. 95-98
37 MEREWETHER, D.E.: 'Transient currents induced
on a metallic body of revolution by an electromagnetic pulse'. IEEE Trans. EMC-13, (2) 1971
38 KUNZ, K.S. and LEE, K.M.: 'A three-dimensional
finite-difference solution of the external response of
an aircraft to a complex transient EM
environment: Part-l - The method and its implementation'. IEEE Trans. EMC-20, (2), 1978
39 As Reference 38, part 2
40 THURLOW, M.H.: 'Evaluation of EMP coupling
of linear systems by swept CW methods'.
Proceedings of lEE colloquium on Protection of
communications equipment against EMP and other
hazards, March 1985, digest 1985/28
41 MORGAN, D.: 'Analysis of EMC susceptibility
data on 23 systems'. Internal report (Class), BAe
Dynamics Ltd, Filton, Bristol, UK
42 'Integrated circuit electromagnetic susceptibility
handbook'. Report MDC E 1929, McDonnell
Douglas Astronautics Company, St Louis, Missouri
63166, USA
43 Elgal EMP and HV Systems, P.O. Box 494,
Karmiel 20101, Israel
44 GILES, j.C.: 'Simulating the nuclear electromagnetic pulse'. Mil. Electron./Countermeas.., August 1977
45 RUDY, T., BERTUCHEZ,j. and WARMISTER,
B.: 'NEMP simulation and tests in Switzerland'.
Third symposium on EA1C, 1979
46 Pulsed power conferences. IEEE Electron Devices
Society, 1987 Washington, 1989 Monterey, USA
47 WILLIAMS, E.R.: 'The electrification of thunderstorms'. Sci. Amer. Nov. 1988, pp. 48-65
48 'World
distribution
and
characteristics
of
atmospheric radio noise'. CCIR Report 322, 1964
49 HORNER, F.: 'Analysis of data from lightning flash
counters'. Proc. IEE,july 1967, 114, p. 916
50 KEISER, B.E.: 'Lightning protection'. Interference
Technology Engineer's Master, 1985, pp. 66-68
51 MIL-B-5087B: 1978 'Bonding electrical and
lightning protection for aerospace systems'
52 SAE ARP: 1978 'Lightning test waveforms and
techniques for aerospace vehicles and hardware'
53 NASA SP 8084: 1974 'Surface atmosphere extremes'
54 PERROTON, G.: 'How to protect hardened
facili ties from very high level transients induced on
power line by lightning or EMP'. Proceedings of
IEEE symposium onEA1C, 1985, pp. 1-4
55 JONES, C.C.R.: 'Latest lightning standards'.
Presented at BAe electromagnetics seminar, BAe
Military Aircraft Ltd, Warton, UK, Nov. 1990
56 BISHOP, j.: 'EMP and lightning testing of avionic
equipments with an introduction to transient effects
to aircraft'. Proceedings of colloquium on Protection
of communications equipment against EMP and other
hazards, March 1985, lEE digest 1985/28
57 DARGI, M.M.: 'Lightning protection testing of full
scale aircraft to determine induced transient levels'.
Proceedings of international conference on Lightning
and static electriciry, September 1989, University of
Bath, UK
58 CARTER, N.J. and HOBBS, R.A.: 'Lightning qualification testing for UK avionic equipment'. Proceedings
of international conference on Lightning and static
electriciry, September 1989, University of Bath, UK
59 WILES, K.G.: 'Lightning protection verification of full
authority
digital
electronic
control
systems'.
Proceedings of international conference on Lightning and
static electricity, September 1989, University of Bath,
UK
60 CLARKE, G.J.: 'The hybrid barrier: protecting
against
EMP
and
lightning'.
Interference
Technology Engineer's Master, 1989, pp. 162-170
61 FIEUX, R.P. et al.: 'Research on artificially
triggered lightning in France, IEEE Trans. P AS-97
(3), 1978, pp. 725-733
62 PODGORSKI, A.S.: 'Composite electromagnetic
threat'. Proceedings of IEEE symposium on EA1C,
1990, pp. 224-227
63 HAR1', W.C. and MALONE, E.W.: 'Lightning
and lightning protection'. Don White Consultants,
Gainesville, Virginia 22065, USA, 1979
64 GERKE, D.: 'Power disturbances and computerised
equipment'. Interference Technology Engineer's
Master, 1990, pp. 302-309
65 FREY, O. and HAEFELY, E.: 'Electromagnetic
compatibility testing of electronic components,
subassemblies, measuring instruments and systems'.
EMC Technol., 1982, pp. 78-83
Chapter 11
Uncertainty analysis: quality control and
test facility certification
11.1 Introduction
fall into in the case of EMC testing where, as will
be seen, there are a great number of factors which
affect the final measurement uncertainty, but for
which there may be no sound theoretical or experimental knowledge of the distributions of individual
error terms.
What follows considers the general trea tmen t of
errors in electrical measurements and then puts
this into context as part of the whole quality
control process for EMC testing. Finally, how the
UK calibration and test laboratory accreditation
service (NAMAS) regulates measurement and
testing activities to ensure sound practice is
examined.
The repeatability of EMC testing depends on
many factors that affect the measurement result.
Some factors are not well understood or not
documented in terms of the nature and
magnitude of their contributions to the total
uncertainty. The treatment of measurement
uncertainty involves the use of statistics to
estimate the probable uncertainty and associated
confidence level with regard to a particular
measurement or set of measurements. Statistics
and probability theory is a considerable subject in
its own right and far too large to deal with
adequately in a book such as this, which is
primarily concerned with the varied aspects of
EMC testing. Useful summaries of the main
theories and analytical techniques are given in a
number of texts [1-5 J and are recommended to
those particularly interested in this aspect of
mathematics, or those who are determined to
achieve a sound grasp of the basics before
considering how to apply them to the understanding of EMC measurement uncertainty.
The application of statistics to experimental
measuremen ts has been dealt with specifically by
Box et al. [6J and Topping [7], and a good understanding of the subject can be achieved via these
texts. Early work carried out in the British
Calibration Service by Dietrich [8J resulted in the
development of a statistical approach to combining
measuremen t uncertainties based on the assumption
of probability distributions for all the contributing
components. In 1977 a useful code of practice was
produced by Harris and Hinton [9J for the
treatment of uncertainty in electrical measurements.
Test engineers should always endeavour to
estimate the errors or uncertainties associated
with the measurements which they make.
However, a superficial and incomplete knowledge
of the statistical treatment of measurement
uncertainty may lead to an unwarranted belief
that an error estimate is correct. In such circumstances it is possible to become complacent and
assume that because some uncertainty analysis is
being done that the measurement results are now
more reliable in some way. This can occasionally
lead to a less searching approach to testing on the
part of engineers. This trap is particularly easy to
11.2 Sotne definitions
Terms that are commonly used in the analysis of
measurement uncertainty [7, 10, 11 J have specific
meanings which should be understood prior to a
general consideration of the statistical treatment
of uncertainty.
True value: the actual value of the quantity being
measured. This is unknowable via measurement.
I t is approximated in practice by the value of the
quantity measured that is established by traceability to national standards [1 OJ.
Measured value: the result of conducting a fixed test
procedure to determine a quantity of interest. In
the statistical treatment of errors its value is
usually denoted by x.
Error: the difference between the measured value
and the true value.
Mean value: the result of computing the arithmetic
mean of a number of measurements. Usually
denoted by x.
Uncertainty: this term quantifies the indeterminacy
in the measurement process by stating the range
of values within which the true value of the
quantity being measured is estimated to lie [10].
This is normally expressed in terms of ± an
absolute number or a % of the mean value.
Confidence: because the limits of uncertainty of a
measurement cannot be known absolutely it is
necessary to qualify them with a statement of
confidence. This is expressed as a percentage; for
example, a confidence value of 95% means that
there is only a 1 in 20 chance or probability that
the true value lies outside the stated uncertainty.
209
210
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
Random error
probability distribution: the result of
plotting the frequency of occurrence of a measured
value as a function of the value. If a large number of
measurements of a quantity are made using the
same procedure and under the same conditions, but
with small random variations, it is found that the
envelope of the probability distribution approxirnates to the 'bell-shaped curve known as the
Gaussian or normal curve. This normal curve was
first derived by de Moivre in 1733 when dealing
with the problems associated with the tossing of
coins. It was also later obtained independently by
Laplace and Gauss. I t is sometimes known as the
Gaussian Law of Errors because it was applied to
the distribution of acciden tal errors in astronomical
and other scientific data. The Gaussian curve IS
derived from the expression
y==A
(x m/
11.1
where A) hand m are constants. The shape of the
curve is given in Figure 11.1. Topping [7J
suggests that 'it is difficult to overstate the
importance of the Gaussian error curve In
statistics as its importance is like that of the
straight line in .ge~metry'. Definitions of a wider
set of terms concerned with uncertainty and
statistics can be found in the UK NAMAS
information sheet NIS 20 [11 J.
Systematic error: one which consistently biases the
measurement (and therefore the mean of n
measurements) in one direction away from the
true value [12J. Examples include a panel meter
with the resting place of the needle not aligned
with the zero mark or an instrument calibration
factor which may be incorrect.
Most uncertainties in real measurements result
from a combination of systematic and random
errors which are introduced via a number of
factors. I t is common to treat these two types of
errors separately as systematic errors that may be
known (within a given uncertainty, by reference
to a national standard) and can be removed from
the measurement by a correction factor, whereas
the uncertainty resulting from random errors can
not. It will be shown that random errors can be
combined with systematic errors to yield a single
value for the uncertainty of a measurement for a
given confidence level.
11.3 MeasureDlent factors
Consider a typical EMC measurement of the RF
current flowing in a multiconductor cable as
depicted in Figure 11.2. There are three main
areas where uncertainty can be introduced into
this measurement.
(i)
(ii)
(iii)
The factors affecting the physical/electrical
environment of all components of the test.
These are sometimes referred to as the
control quantities.
The factors involved with the sensor and its
linkage to the quantity being measured.
These are known as the coupling factors.
The calibration of the measuring instrument
and the way it is used.
This classification of uncertainty factors follows
that given in NAMAS NIS 20 [11] and is
illustrated in Figure 11.3. As an example, some of
CABLE POSITION
P
CURRENT PROBE
TRANSFER IMPEDANCE ( T I )
Figure 11.2
y
Example of uncertainty factors in currentprobe EMC nzeasurement
CONTROL
FACTORS
A
A
B
C
0---"""4
MEASUREMENT
INSTRUMENT
FACTORS
RESULT
I
I
I
I
n
Figure 11.1
Normal error curve y
DATA
x
m
Ae _h
2
R
I
SENSOR
Figure 11.3
(x-m)2
1
CALIBRATION
DATA
Classification of contributions to uncertainty
in measurement
UNCERTAINTY ANALYSIS: QUA.LITY CONTROL AND TEST FACILITY CERTIFICATION
11.4 Random variables
the factors
that
affect
the
measurement
uncertainty for the current-probe measurement
in Figure 11.2 in each of these
are
listed:
The nature of random variables in measurement
can be demonstrated by reference to Figure 11.4.
A number of measurements are made of a
quantity and these are recorded as arrows. The
arithmetic-mean value of the set of measurements is also shown. This, however, will not
necessarily coincide with the mean or central
value for the whole population of possible
measured values. Such a value will be the mean
value of the Gaussian or norlTIal distribution
curve relating to the quantity under investigation. Hinton [7J defines the difference betvveen
the mean of the me:lsuremen t set and the
population mean as an expression of the random
component of uncertainty. I t is not possible to
correct for the uncertainty in trod uced by
random errors; all that can be done is to state a
value
of uncertainty
and
an
associated
confidence level.
In practice, it is found that a relatively small
number of contributions to random uncertainty
which are of similar range can be combined to
produce a distribution which is close to the
normal or Gaussian curve, even if their
individual probability distributions are not
normal (i.e. entirely random) [1 OJ. This is
important in calculating the uncertainty in EMC
measurements where there are a large number of
factors con tri bu ting to the final uncertain ty with
many of them not having purely random distributions.
Pure random variables or measurement errors
are those which are independent of other errors
Control factors
Stability of source and load parameters on the
ends of cable
Position of current probe along the wire (1)
Exact lay-up of wires in the bundle (w)
Angle of current probe to cable axis (a)
Height of cable and probe above ground plane
(h)
Degree to which centre of cable bundle is offset
from centre of current pro be (0)
Position of the connecting cable from probe to
meter (p)
Grounding of meter (g)
Stability of the power supply to meter
Normal physical environmental factors such as
temperature, humidity, etc.
Coupling factors
Current probe transfer impedance as a function
of frequency (1'1)
Connector and cable losses as a function of
frequency (-C1, C2 and A)
Current probe, cable and meter impedances
resulting in VSWR for given cable length
(L)
Measuring instrument
Calibration
correction
factor
and
its
uncertain ty
Signal-to-noise ratio
Operator accuracy in setting up the meter and
in reading and recording the result (R)
r
I
(J)
W
:J
-J
~
LL
o
MEAN VALUE OF ALL I
MEASUREMENTS
WITHIN THE ~
POPULATION
:
CALIBRATION FACTOR
SYSTEMATIC UNCERTAINTY
(can be removed)
I MEAN VALUE
()
w
a::
a::
:J
()
()
J
I
I.FACTTS .1
NORMAL
PROBABILITY .
DISTRIBUTION
o
LL
o
---J
-I
UNCERTAINTY
IN SYSTEMATIC
W
Z
INDIVIDUAL
MEASUREMENT
VALUES IN A
MEASURED SET OF n
~
I
I
I
I
>()
zW
:J
I
I
I
THE CAliBRATION
LABORATORY VALUE
ASSUMED WORST CASE
RECTANGULAR
UNCERTAINTY
DISTRIBUTION
I
VALUE OF
QUANTITY
a
w
fE ..-
.-1
~
_ _ _ _ error for __-__
a
Illustration of measurement uncertainties
~,
measurement no. 3
RANDOM UNCERTAINTY IN THE
MEANS OF THE MEASURED SET
f'igure 11.4
211
THE TRUE VALUE
(unknowable by measurement)
212
A HANDBOOK FOR EMC TESTING·AND MEASUREMENT
(i.e. not related or linked to the same causal
factors) and produce additive effects due to
independent random causes. The mean value of n
measurements is
FREQUENCY OF OCCURRENCE
OF MEASURED VALUES OF x
......-o----t--a--~ 1 STANDARD DEVIATION
11.2
where x == mean value, n == number of measurements, and Xi == value of the ith measurement.
For a random distribution of the variable x it is
possible to derive meaningful quantities known as
the variance and standard deviation which for a
sample population are given by Reference 10 as
11.3
where a 2 == variance of the sample
and
a == standard deviation. Each time a set of n
samples is taken the value of a will change
slightly. The best estimate of the standard
deviation for a whole population of results based
on a single sampIe of n measurements is
a est
so that
In
[n - 1
6
....---+---+-30---+----30"+----+--..... 3 STANDARD
+---+---+----~---+__-_+_-~ DEVIATIONS
x
...---68.3%---10+
.------95.5%------tlIoI
. . . . - - - - - - - 9 9 . 7 % - - - - - - -..
% CONFIDENCE THAT THE TRUE
VALUE OF x LIES IN THIS RANGE OF x
Figure 11.5
Standard deviations and percentage
co1?fidence for normal distribution of values
Table 11.1 Relationship between K and % population
for normal distribution
%population within limits
(x
a a[_n ]~
est
2 0 " - -.........--20"-+--.........
-
n- 1
11.4
11.5
2.58a
and the difference between a est and a is only
significant when the number of measurements n is
small. This standard deviation relating to the
uncertainty in a quantity may be calculated from a
set of measurements, or estimated. The probability
density may follow a normal or Gaussian distribution, a log-normal, Poisson, binomial or other distribution [12]. Information regarding the nature of
these and other types of probability distribution can
be found in Meyer [13J and in a useful NATO
restricted document [14].
Standard deviation is useful because it is an
indicator
of the
range
of measurement
uncertainty for a given distribution. In Figure
11.5 it can be seen that for the Gaussian or
normal distribution there is a 68.3% probability
that any particular measured value will be within
the range ±a of the population mean. Further,
95.5% will be within 2a and 99.7 % within 3a.
Defining the multiplying factor for a asK, then
some further useful relationships between K and
0/0 of population wi thin K a limits can be seen
from Table 11.1 The uncertainty U which
corresponds to a specified %
probability or
confidence factor can now be defined as
U == Ka
0.675a
l.Oa
1.96a
2.0a
11.6
3.Oa
50
68.3
.95
95.5
99
99.7
There is a relationship between the standard
deviation and the parameter h (sometimes called
the precision constant) in eq n. 11.1. I t can be
shown [7J that
1 2
-a
2
11.7
and that A in eqn. 11.1 is taken as
A
h
yin
11.8
and so it is possible to rewrite eqn. 11.1 as
__
1_
y -
0"J2i[
e- (x-x )2;:2
20"
11.9
The value of the standard deviation a for a given
popula tion mean determines the tigh tness of the
density distribution. For example, in Figure
11.6 it can be seen that as a decre~ses the
tightness or precision of the error distribution
increases.
lJNCERTAINTY ANALYSIS: QUALITY CONTROL AND 1'EST FACILITY CERTIFICAl'ION
y
t.-----------
For small samples the normal distribution may
underestimate
the
probabilities
for
large
deviations [13]. Assuming that the density distribution function for the population is Gaussian,
then to calculate the random uncertainty of a
finite sample of measurements to a given
confidence level, it is necessary to use Student's tdis tribu tion [13, 15 J. The random uncertainty of
the mean of a sample of measured values is
·1
2 (21t)-'2
(21t
)~
t
==
o
Figure 11.6
x .....
Normal distribution curves for different
values of (J
y
11.4.1 Student's t-distriblltion
When the measurement of a quantity is only made
a few times the mean value for the set is unlikely to
be the same as that for the whole population of
measurements which could be made. Thus there
is an additional uncertainty associated with the
mean for the set, as shown in Figure 11.2. This
uncertainty decreases by the square root of the
number of measurements made but can be
significant for small values of n, say less than ten.
Table 11.2
213
(Jest
Vn
11.10
where (Jest is the estimate of the standard deviation
derived from eqn. 11.4 and t are the values
specified in Table 11.2 for given confidence levels
and as a function of n, the number of measurements made. I t is clear that as n tends to infinity
the mean for the set tends to the popula tion mean
and U m tends to zero.
Finally, in connection with random distributions,
the standard deviation (Je of the combination of a
number of random distributions each expressed
by a standard deviation (J, is the root sum square
of the contributions:
11.11
11.5 System.atic uncertainty
In determining
uncertainty it is
necessary to consider the measuring apparatus,
Studenf s t-distribution table
Specified confidence level
.......
v
en
v
~
.......
.S
en
.......
~
v
ev
$....i
;:)
en
rj
v
e
4--f
0
$....i
v
..D-
e
;:)
Z
~
0.500
0.683
0.950
0.955
0.990
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
1.000
0.817
0.765
0.741
0.727
0.718
0.711
0.706
0.703
0.700
0.697
0.695
0.694
0.692
0.691
0.690
0.689
0.688
0.688
0.675
1.84
1.32
1.20
1.14
1.11
1.09
1.08
1.07
1.06
1.05
1.05
1.04
1.04
1.04
1.03
1.03
1.03
1.03
1.03
1.00
12.7
4.30
3.18
2.78
2.57
2.45
2.36
2.31
2.26
2.23
2.20
2.18
2.16
2.14
2.13
2.12
2.11
2.10
2.09
1.96
14.0
4.53
3.31
2.87
2.65
2.52
2.43
2.37
2.32
2.28
2.25
2.23
2.21
2.20
2.18
2.17
2.16
2.15
2.14
2.00
9.92
5.84
4.60
4.03
3.71
3.50
3.36
3.25
3.17
3.11
3.05
3.01
2.98
2.95
2.92
2.90
2.88
2.86
2.58
ex:
0.997
9.22
6.62
5.51
4.90
4.53
4.28
4.09
3.96
3.85
3.76
3.69
3.64
3.59
3.54
3.51
3.48
3.45~
3.00
r - - - - Values of't'
214
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
the operational procedure and the item under test.
Systematic bias in a number of individual
measurements can be detected by planned
variation of the measurement conditions and
process, and by averaging the results. The bias
can then be corrected and thus removed froIn
contributing
to
the
total
measurement
uncertain ty.
The calibration of a measurement instrument
with respect to a national standard will reveal
any systematic factor which the instrument or
meter may contain, see Figure 11.4. This can then
be corrected or allowed for by applying the
calibration factor specified in the certificate of
calibration. The calibration laboratory value and
the rnean of the population as shown in Figure
11.4 can then become aligned.
The correction factor given in the calibration
certificate has an error associated with it which is
the systematic uncertainty and is assumed to have
a worst-case rectangular distribution. This
uncertainty, and any other systematic uncertainties which can be identified and quantified, are
first grouped together in accordance with their
known or assumed probability distributions. If
only the limits of the systematic uncertainties are
known it is safest to assume they have rectangular
distributions [10]. They are then combined and
the standard deviation is added to that of the
random uncertainty to yield the full measurement
uncertain ty.
It has been shown [8J and quoted [10, IIJ that
the standard deviation (Js of a systematic
uncertainty having a rectangular distribution
with limits of ± a is
a
11.12
If there are a number of uncorrelated systematic
uncertainties with assumed rectangular distributions with values ± al a2 a3 ... an the combined
standard deviation of the contributions is
aT
+ a~ + a~ ... a~
3
11.13
11.6 COInbining random. and
systen1.atic uncertainties
There are two cases that must be treated
separately vvhen combining systematic and
random
uncertainties:
when
a
dominant
systematic term exists, and when no dominant
systematic term exists. When a dominant
systematic term ad exists in eqn. 11.13 then
Us == K (Js may exceed the arithmetic sum of the
semirange values of the individual contributions.
This can be checked by
n
Us>
L
am
m=l
If this is the case, the dominant systematic
uncertainty contribution should be brought
outside the RSS (root sum square) addition. rrhus
the correct total uncertainty is
I
U=
ad
+
[U/ + U;]
2
2
11.14
where U~, == K (J~ and (J~ is obtained from eqn.
11.13 without including the dominant term ad. U r
is the random uncertainty. When no dominant
systematic term exists the random and systematic
uncertain ties can be combined by the RSS
method as expressed in eq n. 11.11.
For all EMC test engineers and designers of
electronic equipment that may be subject to
EMC testing it is advisable that they should
consult the references listed in this chapter and
gain a working understanding of the statistical
basis for the treatment of measurement errors as
outlined to understand and have confidence in
the results of EMC tests.
11.7 Uncertainties in EMC
n1.easuren1.ents
11.7.1 Contributions to measurement
uncertainty
There are two main problems to be overcome in
generating worthwhile uncertainty statements to
accompany EMC measurements. The first is the
sheer number of variables involved in these
complex measurements and which must be investiga ted and segregated into control, coupling or
instrument factor categories. There may be up to
50
identifiable
contributing
sources
of
uncertainty in, for example, a radiated emission
measurement [12]. This contrasts with a much
more simple measurement of quantities such as
temperature or weight etc. where there may be
less than a dozen significant sources of
uncertainty. As a rule of thumb, used to simplify
matters, one might ignore uncertainty contributions that are smaller by a factor of ten than the
largest contributor.
The second problem relates to obtaining a
meaningful understanding of the nature of the
probability distributions attaching to each of
these uncertainties. This can be done either by
experiment, where each contributing factor is
isolated and studied in a series of careful and
UNCERTAINTY ANALYSIS: QUALITY CONTROL AND TEST FACILITY CERTIFICATION
probably time-consuming controlled experiments,
or by examination of the theory relating to the
factor in question.
The experimental EMC uncertainty database is
generally considered to be poor [12], and as the
generation of definitive data is expensive for
commercial test houses they tend to do only that
necessary to sa tisfy the requirements of the
national accreditation authority, NAMAS in the
UK. A progressive programme to provide
industry
with
a
well
researched
EMC
measurement uncertainty database could be
undertaken by the national metrology authority,
or possibly by combining efforts with those of
other nations to provide a really comprehensive
foundation
for
the
treatment
of EMC
measurement uncertainty.
separately when combining the uncertainties
relevant to that test regime, although in many
cases a common database can be used for
components such as VSWR mismatch, polarisation and antenna positioning uncertainties.
Slightly different uncertainty analyses will result
for variations in a basically common test method
when there are detailed variations required by
particular test standards. For example, consider
two open-range radiated emission tests, one
specified by FCC and the other by VDEjCISPR.
The field averaging uncertainty (Chapter 10)
in trod uced by virtue of the size of the tuned
dipole antenna will be different for the two tests
at frequencies below 80 MHz owing to the CISPR
requirement that the dipole length remains tuned
to 80 MHz for frequencies below this, whereas the
FCC requires the dipole to be tuned down to
30 MHz.
Returning to the uncertainty analysis of a
typical radiated emission test in a screened room,
consider a standard measurement of radiated
emissions from an EDT at 1 m as shown in Figure
11. 7. The factors that contribute uncertainty to
the measurement in the groups identified earlier,
in line with NAMAS NIS 20, i.e. control factors,
coupling factors and instrument factors are listed
in Tables 11.3-5. There is no absolute determination as to which group some uncertainty factors
should be placed in and some control factors may
also be considered as coupling factors. The
definition used in this example is that coupling
factors are those which influence the measurement
11.7.2 Identification of uncertainty
factors
Now examine a typical EMC radiated emission
measurement made in a semianechoic screened
chamber and attempt to identify the more
obvious sources of uncertainty as an example of
the complexity of uncertainty analysis in EMC
testing.
Other test regimes such as open-site testing or
bulk-current injection will have factors contributing to measurement uncertainty that are
particular to them, and no general uncertainty
analysis can be developed to cover widely
differing tests methods. Each must be considered
POWER LINE NOISE
(external)
Penetration of ambients through shielded room
"-...
~
P
'~
- ower
cable
position
Angle subtended by
EUT & cables
...... /
+- / - -----,
x+
~I
I
I
y
Anglesublend~by EUT
I
-=-
t=
I _
----r----
Sign~1
I
cable
position
1
d
_-------
EUT GROUNDING
CONDITIONS
EUT position
PEUT
·
RAM PERFORMANCE
reflections from
walls, floor &
ceilings
~-
r
I.;!
V
ANTENNA
ANGLE
~T:NNA
0
TO ITS REFLECTIONS
NEARFIELD
BOUNDARY?
SWRAT
LOAD
\ r-----[2]~...
EMI METER
-------f'<'-L --;---..
CABLE
~----~
/I\. ..
______
- ANTENNA
_ ----MUTUAL IMPEDANCE
AMBIENT SIGNAL
PENETRATION
SWR
CONNECTOR
- ------------..:
-----=---:SWR ANTENNA
_______
___ SCREENED ROOM
CALIBRATION
FACTOR
(AF)
~--t-.-...-POLARISATION
ANGLE P
-------- M
TYPE & CONFIGURATION
OF GROUND PLANE BENCH
SIGNAL CABLE
EXTERNAL NOISE
Figure 11.7
215
Sources of measurement uncertainty in typical radiated emission test
CABLE
ATTENUATION "A"
216
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
of the electric field
immediate region of
Ineasurement instrument.
from within the
antenna to the
Table 11.5 Instrument uncertainties
EMI meter calibration
calibration shifts are assumed to be
corrected
EMI meter stability with
humidity /altitude
In1pulse generator (internal gain
stability
EMI meter input VSWR
various input
attenuator uvl,L.LL.LC::,~
EMI meter overload (saturation and harmonic/
intermod distortion)
EMI meter spurious signals
EMI meter linearity NB and BB
EMI meter bandwidths and shape factors
EMI meter detector weigh ting functions against
pulse repetition frequency
NB and BB
range
..... TTl-,i-·L1.,""'"i-'"
Table 11.3 Control factors
EUT orientation
EUT
humidity
EU1" grounding
EDT signal cable layout
EUrr signal cable penetrations
EDT power cable layout
EUrr power cable LISN terminations
Ground -plane
ra tio
Ground-plane height
Ground- plane cond uctivi tylintegri ty
Ground-plane bonding to screened room wall
Ingress of external noise through screened room
walls, through penetration panels and along
EUT power and signal cables
Antenna height
Antenna distance from EUT
Antenna mutual impedance to screened room
Antenna
correction
Antenna cable position
External noise on antenna cable
Path loss due to angle subtended by EUT and
cables
Multipath reflections from screened room walls,
floor and ceiling
Screened room size
Screened room absorber efficiency
Position of EDT and antenna in room
Table 11.4 Couplingfactors
An tenna correction factor
'-~ calibration shifts are
assumed to
Antenna size
Antenna polarisation (elevation
Antenna azimuth angle
Antenna polar response (beamwidth and spot
Antenna balun efficiency (differential/commonmode rejection)
Antenna \lSWR
IJ
'-'-d,A.A.,-"," '- ••
Measurement
antenna connector loss and
VSWR
Measurement cable VSWR and length
Measurement cable loss
Measurement cable layout
Measurement
instrument connector loss and
VSWR
Instrument operator related uncertainties
Scan speed/bandwidth choices
Meter reading errors/computer system data
recording errors
In-built software errors
EMI meter parameter recording errors
(e.g. atten. settings, bandwidth records
2/10 dB amplitude scale confusion etc.)
Misnumbered test runs
Incorrect recording of
amplifiers
in line to EMI meter
Proced ural or· da ta recording errors
at
shift handover times in test facili ty
11.7.3 Estimation
uncertain ty
For each of the identified
the EMC
test engineer needs to estimate the level of random
and
uncertain ties and express these in
terms of a standard deviation for a particular type
of
function. In some cases the
factors may
rise to a contribution to both
random and
types of uncertainty.
The total uncertainty for the random and
errors can be calculated by
.I.''Fthe standard deviations for each as shown
if they are substantially independent of each
even if the density functions are not
Gaussian. This is a useful property of the central
limit theorem [13]. Depending on whether there
is a dominant systematic contribution, the
random and systematic uncertainties can be
accumulated according to eqns. 11.11 or 11.14.
I t is unreasonable to carry out a detailed
uncertainty analysis for all EMC tests taking into
account all of the possible influencing factors such
as those listed, for the radiated emission test in a
screened room. The experienced EMC test
engineer should be able to rank the uncertainties
1J'-'-'J.A.A."""c"'",,-",,
"-'''-'J.LI.U'",,-LI..I..
UNCERT'AINTY ANALYSIS: QUALITY CONrrROL AND TEST FACILITY CERTIFICATION
introduced by the various factors so that only the
major ones need to be included in the formal
statistical analysis. This will greatly reduce the
work needed to arrive at a satisfactory estimate of
measurement
uncertainty.
The
NAMAS
executive [11 J require EMC test houses to
formally present, during a quality audit surveillance visit, at least one such analysis carried out
on a test during the last year.
Examples of the magnitude of the uncertainty
associated with the most important factors
relating to the radiated emission test in the screen
room follow. Strictly, one should not use the
logarithmic term decibel to represent an
uncertainty range, as figures should be expressed
as a linear factor. However it has become
common practice in test laboratories to use the dB
and it is widely quoted in References 12 and 17.
•
EUT placement: Very dependent on the type
of EUT and its radiation pattern. Default
value (J == 6 dB.
Screened room reflections: Dependent on size
of room, location of antenna and EUT and
anechoic damping. For a room with no
anechoic lining and below first resonance
(J
2 dB [16, 17J. Above first resonance and
up to 5x this frequency (J == 7 dB [16, 17]. An
exam.ple of the difference between EUT to
an tenna coupling for an open site and a
screened room, given the same test configuration, is shown in Figure 11.8 [18, 19]. It can
be seen that the worst-case differences are up
to ±40 dB. I t would be interesting to analyse
the density distribution of the occurrence of
differences to see if it was normal, log-normal
or another well known type. For a screened
room with RAM lining giving 6 dB reflection
loss at 30 MHz it is possible to reduce the
reflection uncertainty to (J == 3 dB above
30 MHz and (J == 2 dB above 100 MHz [1 7J .
•
(j)
(j)
~
~~
50-----------.....,.-....-----..,...---.,
30
Zz
20
10
w w co
•
•
•
40
ww
~~
•
0t.=:=======:=:II~t-'I,..,PI
~~'O -10
~~
-20
00
-30
~~
-50
~~
6~
-40
•
L..-_ _- - - I _.........
....._ ~ - _ - ~ - - -
Go
Z
Figure 11.8
Coupling between antennas in shielded room
as function offrequency-' with 1 m spacing
*Coupling normalised by r~ference to opensite antenna coupling values
217
Polarisation uncertainty: White [12J shows
that the uncertainty in measuring a maximum
E-field due to an element of cross polarisation
is composed of an offset mean of -6 dB and
an uncertainty with (J == 6 dB. This comes
about because the probability of making a
measurement, other than for perfectly aligned
polarisation, must always result in a lower
than true reading. Assuming that a dipole-like
antenna has nulls at -20 dB below the peak
response and that all polarisations of waves
from the EU1' are equally likely, it can be
shown that the figures quoted above are
realistic even though the distribution is not
Gaussian.
VSWR mismatches: If a typical biconic
antenna has a VSWR of 3: 1 it can be shown
[17J that the uncertainty can be represented
by (J
2.9 dB. For a receiver with an input
VSWR of 2: 1 there is another additional
uncertainty of 1.9 dB. Taken together the
combined uncertainty will be represented by
(J == 3.5 dB.
Antenna calibration uncertainty: There is very
little reliable information regarding the
uncertain ty associa ted wi th the use of
commercial passive antennas. I t is clear that
varia tions in the manufacturers' calibration
cannot be~ .ignored as these calibration curves
must usually be used. I t is very difficult to
calibrate one's own antennas by comparison
to industry reference standards or to calibrate
thern by generating known fields. The NPL
published uncertainty [20J in calibration for
antennas below 1 GHz is ±1 dB excluding
large loops (assuming a rectangular distribution for systematic uncertainty) , ( J
0.5 dB
approx. This is almost insignificant, but when
other factors such as ageing in use, loose
elements, worn connectors are included,
White [12J suggests it is prudent to allow for
(J
3 dB.
Antenna cable/balun effects: Uncertainties due
to antenna cable, antenna element and
antenna cable and poor balun effects have
been estimated by DeMarinis [21 ] to
introduce uncertainties with a maximum
value of up to 12 dB. Assuming this to be
representing a 3(J case one may estimate the
standard deviation to be around (J == 3-4 dB.
Field averaging: Estimates of worst-case
uncertain ty for field averaging introd uced into
an open-range measurement with a tuned
dipole at 30 MHz have been produced by
Brench [22]. He gives values of -8.5 dB lower
than would be expected from a point
measurement. If some systematic correction is
made, for say half this range, it may be
218
•
•
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
reasonable to set a value for (J
2 dB at
< 80 MHz falling to < 1 dB above 80 MHz.
The 1 dB value is relevant to screened room
testing where only short dipoles are used.
EM! meter uncertainty: This is generally
quoted as having a worst-case
value of ±2 dB. This would' lead to an
estimation for the standard deviation of
< 1 dB.
Near-field uncertainty: White [17] quotes
values for the uncertainty in a 3 m open-range
FCC test with a dipole at 30 MHz as being
(J
< 1 dB. It is unlikely that the figure V\Till
be so low for MIL S1-'D measurements made
at 1 m in a screened room.
11.7
Estima te of total urlcertainty
White [12]
a comprehensive account of
estimating EMC measurelnent uncertainties on
the basis that most probability density functions
for con tribu ting factors are largely unknown or
not documented, and over a limited range of ±(J
may be represented by a log-normal distribution.
l'his is a distribution where the random variable
x has a logarithm which is normally distributed
[13]. Thus White gives standard deviations
expressed in dEs and sun1med according to eqn.
11.11. While this is certainly convenient, one
must be careful to establish its validity in each
particular circumstance.
Combining the estimates of standard deviations
given earlier for the major factors which contribute
to measurement uncertainty of our example test in
a screened room, using eqn. 11.11 (assuming no
totally dominant contribution) we arrive at a
value of (Jtotal == 10.6 dB. This is higher than the
figure given by Dash [23J, produced by analysing
actual test data from open-range sites derived from
measuring the same EUl' at a number of
government facilities in different countries. l'his
should not be surprising, as the extra contribution
to uncertainty from standing waves in the shieldedroom case will increase the total measurement
uncertainty. The standard deviation quoted by
Dash for the open site is 8.5 dB.
The example calculation of uncertainty in the
measurement of radiated emissions fron1 an EU'f
at 1 m in a screened room has been carried out as
an illustrative exercise to demonstrate the nature
of
factors and to suggest reasonable
magnitudes
their standard deviations. 1-'he
reader should take the values suggested as being
indicative only, and should carefully evaluate the
statistical distributions and estimate standard
deviations for contributing factors with reference
to particular test configurations and operating
11 . 8 Test laboratory llleasuretnent
uncertainty
11.8.1 NAMAS
The authority responsible for test/calibration
laboratory accreditation in the UK is the
National Measurement Accreditation
NAMAS, formed in 1985. The organisation
developed from the National Testing Laboratory
Accredita tion Scherne and the Bri tish Calibration
Service. NAMAS document MIO [24J, 'General
criteria of competence for cali bra tion and
laboratories' replaces the BCS EO 102 'Approval
calibration laboratories' and the NATLAS Nl
document. '[he principles on which document
M lOis based are consistent with those given in
ISO Guide 25: 'General requirements for the
technical competence of testing laboratories', and
EN4500I: 'General criteria for the operation of
testing laboratories', which standard calls up the
relevant requirements of BS 7581: 'Measurement
and calibration systems'.
Laboratories accredited
NAMAS meet the
requirements of ISO 25 and EN4500I and are
considered as meeting the req uirernen ts concerned
with the adequacy of calibration and testing
contained in IS09000, EN29000 and BS5750
series of specifications, relating to
assurance in manufacture and similar
Details of contact names and telephone numbers
for staff in the NAMAS executive are available
[25].
NAMAS does not accredit laboratories to
approve products [11]. This is the role of the
appropriate national certification bodies such as
the DTI Radio Communications ])ept in the UK,
the FTZ in Germany and the FCC in the USA.
The reports produced by accredited competent
laboratories
concerning
the
EMC
test
measurement of a product is usually the basis on
which the certification body will grant approval
for sale and operation.
11.8.2 NAMAS and measurement
uncertainty
The broad policy and details of statistical methods
to be used by accredited laboratories when
assessing measurement errors are con tained in
publications NIS 20 [11 J and B3003 [26].
NAMAS requires that test laboratories shall have
sufficient understanding of measurement, such
that their measurements, or statement of
compliance or noncompliance 'can be defended
beyond all reasonable doubt'.
NAMAS policy aims to minimise doubt which
could result from a difference of opinion with
UNCERTAINTY ANALYSIS: QUALITY CONTROL AND TEST FACILITY CERTIFICATION
respect to the compliance or otherwise of a
particular product. Laboratories are therefore
required to be able to make corrections for error
where appropriate, and having done so, to
evaluate the overall uncertainty when carrying
out testing. The role of NIS 20 [11] is to enable
laboratories to understand the NAMAS requiremen ts with regard to uncertainty in measurement
and to be able to evaluate the total uncertainty
using a statistical approach.
Test reports must carry a statement of total
measurement uncertainty and therefore laboratories are required to have a documented policy
in line with NIS 20 on measurement uncertainty,
which guides staff in the preparation of such
statements. Laboratories must produce and meet
a NAMAS-approved laboratory schedule of limits
of error and uncertainty (known as Schedule A),
for all quantities for which measurement accreditation is claimed.
The applicant laboratory decides the level of
uncertainty for which it wishes to be accredited,
bu t the limits cannot exceed those specified in
appendix 4 of NIS 20 and each limit set out in
Schedule A must be justified by an uncertainty
budget and calculation. At least one uncertainty
evaluation for an accredited test must be
available for inspection each year during the
NAMAS surveillance visit. Within the UK,
NAMAS prefers that the uncertainty in a given
test be evaluated at the 95% confidence level.
This is a convenient point to look briefly at the
statistical approach which is widely adopted to
the statement of compliance of a sample of massproduced items with the interference limits
stipulated in EMC standards. The statement of
compliance is made after the test, or possibly
multiple tests, of a batch of units, with the results
being analysed according to a set of statistical
rules.
11.8.3 Limits and production testing
In the wider field of sample testing for product
approval, the CISPR publication 16 (section 9)
[27J requires that 'compliance of mass-produced
appliances with radio interference limits should be
based on the application of statistical techniques
to assure the consumer with an 80% degree of
confidence that 80% of the appliances being investiga ted are below the specified limit'. This is the so
called 80% /80 % rule and details of the statistical
techniques are given in Reference 26.
Dvorak [28] gives data on practical measurements made on samples (up to ten) of angle
grinder and hand-drill electric power tools and
discusses the statistical techniq ues used to reach a
statement of compliance. He suggests that very
219
Iittle of value has been published on a rational
engineering approach to the problem of setting
limits to ensure interference control. However,
this is crucial if technically derived limits are to
be implemented within realistic economic
constraints for mass produced products. Absolute
limits (no interference from any product shall
exceed a stated value) are not unreasonable for
small numbers of specialist devices, but a
statistical analysis is far more appropriate to the
EMC clearance of mass produced items. Many of
the equations given in Section 11.4-11.6 are
applicable to the calculations which need to be
performed.
Compliance with a limit L can be judged from
xn + Ka n < L
where x == arithmetic mean of n samples, K is a
factor related to confidence level for a given
sample size, and an == standard deviation of the
sample of size n. To generate a high degree of
manufacturer confidence that the testing carried
out on equipment does lead to a credible
statement of compliance, it is necessary to test
samples of up to ten randomly selected examples
of the product and perhaps to repeat the testing
of the sample a few times [28J. This will
inevitably be rather time consuming and therefore
expensive, but should lead to the absolute
minimum of product compliance rejections
without
sound
cause.
An
early
CISPR
Recommendation [29] gives the procedure to be
used for testing appliances in large-scale
production.
11.9 NAMAS requirem.ents for
laboratory accreditation
11.9.1 Requirements for accreditation
Companies which conduct EMC testing and wish
to gain NAMAS accreditation must be prepared
to submit to the requirements set out in NAMAS
documen ts M 10 [24] and M 11 [30] . The
princi pal req uiremen ts follow.
The laboratory must be legally identifiable.
Paying due fees to NAMAS.
Giving such undertakings as NAMAS may
reqUIre
Being subject to reassessment every 3-4 years,
and surveillance visits every year, with the
possibility of unscheduled surveillance visits.
The laboratory cannot make use of unreasonable or irresponsible subcontracting.
The laboratory must abide by the law of the
land.
The laboratory must be impartial, and the
220
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
staff shall be free from any commercial,
financial or other pressures which might
influence their technical judgment.
The laboratory must afford the client whose
product is being tested reasonable cooperation so that the performance of the
laboratory can be monitored.
The
laboratory
must
afford
NAMAS
reasonable accommodation and co-operation
to enable their representative to monitor
compliance with the regulations.
Key staff in the laboratory must have job
descriptions and be aware of their roles and
the extent and limitations of their responsibilities. Specification of the qualifications,
training and experience necessary for the key
managerial and technical staff shall be
contained in the job descriptions. The
laboratory shall normally use only staff who
are permanently employed or on contract to
the laboratory.
There shall be a documented policy to ensure
that new and existing staff maintain relevant
academic expertise, technical skills and professional expertise.
ManageriaJ staff shall have the authority and
resources needed to discharge their duties.
The laboratory must have a documented
policy and procedures to ensure the protection
of proprietary
rights
and
confidential
information concerning products being tested.
The laboratory should
have restricted
physical access for unauthorised individuals.
There must be named laboratory and quality
managers with responsibility for all work
undertaken. The quality manager must have
direct access to the highest level of
management which is concerned with the
company policies which affect the laboratory.
The
laboratory
shall
have
nominated
authorised signatories recognised by NAMAS.
A q uali ty system shall be formalised in a
quality manual which meets the requirements
ofNAMAS document M16 [31]. The manual
must be maintained up to date.
The laboratory must establish and maintain
proced ures to control the distribu tion,
updating and retrieval of all documentation
that relates to the calibration or tests it
performs. Amendments to the documentation
shall be subject to strict management control.
The laboratory quality manager must plan
and ensure that periodic internal audits of
proced ure and operation are carried out.
They shall be conducted as freq uently as
necessary to achieve the required level of
quality control. The period between audits
shall not exceed 1 year.
The laboratory shall normally use only
equipment that is owned by, or on long lease
or loan to the laboratory. It shall be suitable
for all the tests for which it is to be used and
must be capable of achieving the accuracy
req uired. I t should be of established design if
possible and be operated only by named
authorised staff. Each items of equipment
should be uniquely identifiable.
i\n up-to-date calibration history of equipment
req uiring calibration shall be maintained and
available for inspection.
The laboratory shall, wherever possible, ensure
that any data recording and analysis computer
software is fully documented and validated
before use.
The standard of accommodation and facilities
shall be such as to facilitate proper
performance of the tests. Effective monitoring
and control of environmental factors shall
take place. Due attention shall be paid to
factors such as mains voltage, electromagnetic
interference, humidity, temperature, dust and
vi bration levels.
The laboratory shall have an effective
documented system for identifying test items.
There must be a systematic and documented
record of all information of practical
relevance to the tests performed. All records
must be maintained for a period not less than
6 years.
11.9.2 Advantages of laboratory
accreditation
The examples of the requirements that a NAMAS
accredited EMC test laboratory must meet are
stringent and involve the laboratory in some
time, trouble and cost. The accreditation may be
taken as an indication that the req uiremen ts set
out are being met by the laboratory on a daily
basis.
For
a
manufacturer
reqUIrIng
EMC
conformance testing the use of an accredited
laboratory offers a number of advantages in terms
of confidence in the q uali ty of test reports
obtained. A major one is the acceptance of third
part certification by customers, avoiding the need
for each customer to carry out a separate
assessment. A list of accredited laboratories (at
the time of writing) is given in NAMAS Concise
Directory M3 [32].
Not all EMC tests need to be carried out in
NAMAS
approved
facilities;
adequate
development or preconformance testing can be
done in other laboratories, or by the manufacturers themselves. Under the terms of the EC
harmonisation directive 89/336/EMC self certifica-
UNCER1'AINTY ANALYSIS: QUALITY CONTROL AND TEST FACILITY CERTIFICATION
tion of product EMC performance by manufacturers using their own facilities is permitted. It
may be in the interests of self certifying Inanufacturers to obtain NAMAS accreditation for EMC
testing if they wish to convince customers they are
working to the highest q uali ty standards, or offer
a testing service to other companies.
NAMAS-accredited laboratories may become
the core of competent bodies referred to in the
harmonisation legislation who can assess the
EMC performance of a new equipment by
studying the technical file which is built up
during the development programme. If the
assessmen t is posi tive it is possible to certify
compliance with the relevant standards called
up in the legislation wi thou t recourse to a full/ /
EMC test. Thus the generation and submission
of the technical file to a N AMAS/ liboratory
could be the preferred route to EMC
compliance if the equipment is large, difficult
and expensive to test.
The electrical measurements division of the
National Physical Laboratory and the NAMAS
executive are approachable and will help in the
understanding and interpretation of technical and
quality requirements which relate to EMC testing
in the UK. EMC test facility managers and
engineers,
together
wi th
managers
and
development engineers in firms producing
products which require EMC clearance, should
study carefully the NPL/NAMAS documentation
referred to in this chapter to appreciate the
framework within which EMC compliance testing
is carried out in the UK.
11.10 References
2
3
4
5
6
7
8
9
SPIEGEL, M.R.: 'Probability and statistics'
(McGraw Hill, 1988, SI edn.)
FELLER, W.: 'An introduction to probability
theory and its applications' (Wiley, 3rd edn.)
BEAUMONT, G.P.: 'Probability and random
variables' (Wiley)
HARPER, W.M.: 'Statistics' (Macdonald & Evans,
London, 1965)
TUCKWELL, H.C.: 'Elementary applications of
probability theory' (Chapman & Hall, London)
BOX, G.E.P., HUNTER, W.G. and HUN'TER,
j.S.: 'Statistics for experimenters: An introduction to design, data analysis and model building'
(Wiley)
TOPPING, j.: 'Errors of observation and their
treatment' (Chapman & Hall, London)
DIETRICH, C.F.: 'Uncertainty, calibration &
probability' (Adam Hilger, 1973)
HARRIS, LA. and HINTON, L.J.T.: 'The
expression of uncertainty in electrical measurements'. BCS guidance publication 3003, issue 1,
1977
221
10 HINTON, L.J.T.: 'Uncertainty and confidence in
rneasurements'
in
BAILEY,
A.E.
(Ed.):
'Microwave measurements' (Peter Peregrinus,
London, 2nd edn., 1989) Chap. 25
II NAMAS information sheet NIS 20. NAMAS
Executive,
National
Physical
Laboratory,
Teddington, Middlesex, TWll OLW
12 WHITE, D.R.J.: 'A handbook series on electromagnetic interference and compatibility, volume 2 EMI test methods and procedures'. Don White
Consultants, Germantown, Maryland, USA, Chap. 5
13 MEYER, S.L.: 'Data analysis for scientists and
engineers' (Wiley)
14 'Statistics, probability and reliability' . NATO ES/
CISG/71, draft issue C 1986, Chap. 4
15 GOSSETT, W.S.: 'Student's 't' distribution'.
(Statistician to Guinness Brewery, UK)
16 Shielded enclosure performance measurernen t
program. APG contract DDAD05-77-9551, USA
17 WHITE, D.R.J. and MARDIGUIAN, l\r1.: 'Errors
in EMC compliance testing and their control'. Don
lvVhite Consultants Inc, Gainesville, Virginia 22065,
USA
18 HEIRMAN, D.N.: 'Education and training of the
industrial regulatory compliance test team'.
Proceedings of IEEE symposium on EMC) 1981,
pp. 365-368
19 FREE,
W.R.
and
S'TUCKEY,
C.W.:
'Electromagnetic interference methodology, communications equipment'. Technical report ECOM
0189-F, NTIS AD 696496, Oct. 1969
20 'RF and microwave measurements'. NPL 00/1.5K/
NI/9/90,
National
Physical
Laboratory,
Teddington, Middlesex, TWll OLW, UK
21 DE MARINIS,j.: 'The antenna cable as a source of
error in EMI Measurements'. Proceedings of IEEE
symposium on EMC) 1988, pp. 9-14
22 BRENCH, C.E.: 'Antenna differences and their
influence on radiated emission measurements'.
Proceedings of IEEE symposium on EMC) 1990,
pp. 440-443
23 DASH, G.: 'Computing equiplnent standards -- An
update on cable and peripheral placement'.
Proceedings of IEEE symposium on EN/C, 1987,
pp. 332-337
24 NAMAS accreditation standard: General criteria of
competence for calibration and testing laboratories,
MI0. NAMAS Executive, National Physical
Laboratory, Teddington, Middlesex, TWll OLW
25 'NPL points of contact'. NPL0004/8K/Nj /6/90,
National
Physical
Laboratory,
Teddington,
Middlesex, TW11 OLW, UK, pp. 36,37
26 'The expression of uncertainties in electrical
measurements B3003'. NAMAS Executive, NPL
Teddington, Middlesex, 1'W11 OLW (Related to
Ref. 9)
27 'Specification for the radio interference measuring
apparatus and measurement methods, section 9:
Statistical considerations in the determination of
limits of radio interference'. CISPR 16
28 DVORAK, T.J.: 'The problems of limits interpretation in type approval testing and production
control'. Proceedings of IEEE symposium on EMC,
1981, pp. 264-268
222
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
29 'Compliance with limits in large scale production'.
CISPR Recommendation 19, publication 7
30 'Regulations to be met by calibration and testing
laboratories'. Publication M 11, NAMAS Executive,
NPL, Teddington, Middlesex, TWll OLW, UK
31 'The quality manual: Guidance for preparation'.
Publication M16, NAMAS Executive, NPL,
Teddington, Middlesex, TWll OLW, UK
32 'NAMAS concise directory'. Publication M3,
August 1990, edn. 5, NAMAS Executive, National
Physical Laboratory, Teddington, Middlesex,
TWll OLW, UK
Chapter 12
Designing to avoid EMC problems
EMC has not been quantified. Production
variability can then lead to EMC problems
manifesting themselves in some proportion of the
units manufactured.
Design is an iterative feedback process which
involves continued interaction between required
performance
and
technical
and
financial
constraints. I t involves the synthesis of system
archi tecture and the development of stra tegies and
techniques by which the product performance
goals can be met in the optimum cost-effective
manner within the imposed project constraints.
In general, it is the designer who is technically
responsible for every significant aspect and result
of his design. But EMC problems can often arise
from obscure causes which may not be significant
in terms of the design strategy adopted to meet
the primary design goals. The designer can call
for assistance in the form of an EMC specialist,
possibly an external consultant who will provide
the background knowledge and expertise to
advise the designer and his team about aspects of
their proposed design which may lead to EMC
problems. Together they can then work out a set
of modifications which improve the EMC
performance of the design without compromising
the original design goals.
Whilst this approach does work, it necessarily
sets the EMC expert apart frorn the main design
effort and can cast him in the role of the
opposition, an extra qualification on the design
which is being developed. In these circumstances
EM C engineering tends to con tin ue as a
discipline outside that of mainstream electronic
design and the situation is repeated again and
again, as EMC knowledge stays with the EMC
expert and is not transferred and integrated into
the product design team. To do so requires
company management to realise that EMC
problems and solutions do not fit neatly into
watertight design compartments, nor can it be
dealt with at a single level of technical staff and
management. EMC is a vital part of product
design and the best way to ensure success is to set
aside time and funds to train existing designers and
to recognise the value of using multidiscipline
ElVIC skills as just one part of the formal design
process. See Figure 12.1.
Consultants can still occasionally be brought in
to supplement the EMC knowledge required for
12.1 Intrasystetn and intersystetn
EMC
Electromagnetic compatibility is likely to play an
increasingly important role in both electronic
engineering and commercial law during the 1990s
[1]. rrhe overuse of the EM spectrum, the rapid
inclusion of microprocessors into a very wide
range of industrial, commercial and domestic
equipment, and the increased awareness of
possible effects of EM energy on biological
systems will bring this abou t. Electromagnetic
compatibility has emerged from the world of
military and space systems manufacture, to
contribute to the performance of everyday
electronic equipment and the profitability of
companies engaged in its supply.
There are two kinds of electromagnetic compatibility which a system or equipment designer must
consider: intrasystem compatibility, which is
concerned with EMI internal to an equipment,
and intersystem compatibility, which is concerned
with EMI external to the equipment. This
involves compatibility with other equipments or
systems
in
its
immediate
electromagnetic
environment and the safeguarding of the wider
EM spectrum.
12.1.1 Intrasystem EMC
Internal
electromagnetic
compatibility
is
important for the equipment to function properly
in its own right. Without careful EMC design,
circuits can interfere with each other and this
leads to unreliable and degraded operation,
unnecessary expensive field support engineering
and possibly a loss of customer confidence in the
product. Electronic designers have a great
number of problems to consider and sometimes
only recognise EMC when it becomes a problem,
usually close to the end of the design stage when
it is far too late to effect low-cost solutions. In the
past, electronic designers have sometimes designed
with only the obvious product design goals in
mind, and have not recognised the need for a
formal approach to EMC to be considered as an
integral part of the design process. Thus
equipments have sometimes been produced where
the margin between successful operation and
degraded performance due to a lack of internal
223
224
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
ELECTRICAL
DESIGN
I
I
r------i
y
REQUIRED
EQUIPMENT
PERFORMANCE
H
SOFTWARE
DESIGN
ENVIRONMENTAL
ENGINEERING
Figure 12.1
EMC is just one important product design
feature
certain tasks, but the long term goal of the
company should be to access education and
training programmes [2-5J to build an EMC
design knowledge base wi thin the normal design
teams.
The need for management to provide training
support for staff to ensure good EMC design,
especially for companies producing commercial
electronics, is sometimes not understood. This
may stem from the multifaceted nature of EMC
and the difficulties which arise in quantifying the
benefit to be gained by a formal EMC
programlne being carried out by the design team,
when compared with the investment which is
needed for their training and support.
The situa tion has been a little clearer for
companies in the military and aerospace sectors
which have been contracted to meet EMC
standards, and formally demonstrate product
compliance. Legally enforceable EMC standards
are being introduced in the UK in the first half of
the 1990s to regulate the EMI from commercial
electronic products. When this happens, and the
penalties for noncompliance are known, the cost
benefit in pursuing good EMC design will be
much more obvious.
12.1.2 Design for formal EMC
compliance
Wi th the adven t of these mandatory regulations
concerned with the electromagnetic compatibility
of almost all commercial electronic equipment,
EMC has come to be associated by some
principally with those procedures and practices
which will ensure compliance v\lith standards.
l'his is perhaps a narrow view and fails to
recognise the reliability and other performance/
quality benefits which good intrasystem EMC
design can bring to the product to increase its
competi tive edge in the market.
A successful EMC design requires more than
slavish adherence to a set of design rules and
practices, useful though these are. Designers must
have the knowledge to design in EMC from the
earliest stage in the development process with flair
and invention.
The existence of a specified external EM
environment in the relevant standard is the
starting point for the intersystem EMC designer,
who knows what performance must be met. In
the case of designing purely for internal compatibility, one must attempt to specify both the
emission and susceptibility levels for the
equipment and set an affordable margin of
compatibility.
Designers of military equipment are familiar
with the formal control of the EMC design and
certification process as required by the relevant
MIL or DEF standards. Much of the approach is
transferable to commercial equipment design
teams without imposing unnecessary technical
constraints or costing too much.
The general approach is outlined next.
12.1.2.1 Contractual assistance
EMC expertise is required to establish and agree a
satisfactory contract for the equipment to be
produced. In the simplest case this may only
involve interpreting the technical and cost impact
of the legal requirements flowing from EEC/89/
336 and appropriate technical standards for
equipment to be sold within the EEC. For
/equipment to be sold worldwide, careful
assessment of the multitude of country and
trading block EMC standards and regulations
must be made to establish equivalences and
understand which regulations take precedence.
Only when this has been completed can the
worst-case composite specification be defined and
its impact reflected in the contract and price.
12.1.2.2 EMC control plan
The evolution of a satisfactory EMC design that
can meet the contractual req uiremen ts should be
ensured by the control afforded by adequa te documentation, design reviews and for large projects,
the referral of key design decisions to an EM C
control board. The top-level control plan will
specify how the design is to be controlled, by
whom and with what means.
12.1.2.3 System specification
The contractual requirement for EMC will be
interpreted into design req uiremen ts in the form
of system and subsystem EMC budgets as shown
in Figure 12.2. These documents can be simple in
the case of a commercial product that only has to
meet, for example IEC 801, or may be complex
in the case of a military equipment or large
commercial system. The subsystem specifications
DESIGNING TO AVOID EMC PROBLEMS
225
Figure 12.2 Top-level EMC
design process
EMC DESIGN
BUDGET CONSTRAINTS
SIMPLE EMI
COUPLING MODELS
EMC TECHNICAL APPROACH
EMC TECHNICAL
DATABASE
(Case histories!
Expert system/
Consultants)
- a design methodology for
cost-effective balanced
hardening
EMC DESIGN
HANDBOOKS
- detail technical
options
CO-ORDINATED EMC DESIGN
AND TESTING PROGRAMME
CONTROLLED BY EMC CONTROL
AND TEST PLANS
will reflect the need of the product to meet the
imposed external EMC specifications and the
need to achieve internal compatibility.
Clear understanding of the technical aspects of
EMC is important at this stage as the apportionment of the contractual and internal EMC
requirements down to subsystem level affects the
cost of optimum design for compliance with
imposed standards and correct equipment
functioning. The systems engineers or designers
must have a good understanding of EMC
hardening methodologies [6-8J and be capable of
running trade-off studies between various possible
hardening solutions to select the best overall
system philosophy.
12.1.2.4 Design handbooks
Often design engineers engaged on EMC will make
use of a wide range of general design hand books to
aid their work. Some are produced by the Military
[9-12J and various books and notes [8, 13-15 J
have been written which include information on
EMC design. Although some of the basic
techniques are reviewed in this book, it is not
intended to deal in depth with EMC design
techniq ues, as the subject is well covered elsewhere.
Companies which have a longstanding need for
cornpetence in EMC design often produce their
own handbooks for the guidance of electronic and
other engIneers. However, these are
company confidential documents as they
the results of hard-learned lessons in the
EMC design.
Design handbooks will typically include
the following topics:
usually
contain
field of
data on
Bonding: types, corrosion, vibration
Grounding: LF/HF/VHF solutions
Filtering: passive, lumped/distributed, absorbative
EMC aspects of mechanical design: box
fabrication, seams, materials
Shielding: materials, penetrations and apertures
Cable design: coupling, screening, routing,
segrega tion
Connectors: type, use, shielding, connection to
cable screens
Circuit board design: ground planes,
decoupling, loop areas, inductance and stray
capacitance
Component placement and orientation
IC logic selection: speed, noise emission and
susceptibility
Power supplies: regulation, noise emission,
susceptibili ty
Optoisolators and fibre optics
Transformers: mains, audio, video, "RF
Common-mode /differen tial- mod e interfaces
Interface circuit protection
Electrical safety req uiremen ts.
226
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
12.1.2.5 EMC computer modelling
eg. own subsystem,
other system, external
lEM environment
Figure 12.3
I
real coupling USUallY}
{ involves parallel paths
l
eg. own subsystem,
own system, other
system, the general
EM environment
Extensive EMC system-level computer models
have been constructed in the past for military and
space programmes such as SEMCAP [16] (systen1
and
electromagnetic
compatibility
analysis
program) bu t the use of such a program is
perhaps inappropriate to all but the largest
projects. Smaller versions have been produced
which are better for smaller projects, but these
complex software packages have not been
universally adopted as the best way of estimating
potential EMC problems.
Other EMC system software has been developed
largely in the US, and is described by Keiser [13].
These models include IPP-1 (interference prediction
process) and IEMCAP (intrasystem electromagnetic
compatibility analysis program) which determine
whether a coupling path exists between any two
nominated subsystems/units as shown in Figure 12.4.
Appropriate transfer function or coupling models are
then used to determine the level of potential incompatabilities between the various subsystems.
The incompatibility identification process can be
visualised in the form of a set of ma trices as shown
in Figure 12.5. The matrix is composed of columns
of subsystems defined as ABC D etc. which are
I
Block diagram of the generalised EMI
situation
The configuration of these design elements into a
complete EMC equipment design is a task
req uiring considerable theoretical and practical
knowledge and experience. In a real system the
transfer of EM energy can occur at subsystem
level (wi thin the system), or between the system
and its EM environment and between the system
and other systems. Depending largely on the
distances between the coupled elements, the
circuit impedances and the frequency of the EM
energy being coupled, the coupling paths can be
considered to fall in to three broad types, as shown
in Figure 12.3. All possible paths or combinations
of paths must be addressed in a competent EMC
design.
Figure 12.4 Illustrative
example oj intrasystem
coupling paths
EXAMPLE SYSTEM (transmitter)
POWER AMPLIFIER
SUBSYSTEM ICI
POWER SUPPLY
OSCILLATOR
SUBSYSTEM IN ~-.:...._----.. SUBSYSTEM IB I
PROBABLE COUPLING PATHS
LIST OF CONDUCTED EMISSIONS
LIST OF RADIATED EMISSIONS
SUBSYSTEM 'A'c
CULPRIT
(Psu)
CE
RE
SUBSYSTEM 'B l c
CULPRIT
(oscillator)
LIST OF CONDo SUSCEPTIBILITY
LIST OF RAD. SUSCEPTIBILITY
SUBSYSTEM IA'v
VICTIM
(Psu)
cS
RS
SUBSYSTEM'SSv
VICTIM
(oscillator)
CE
CS
RS
RE
SUBSYSTEM 'C'c
CULPRIT
(PA & antenna)
SUBSYSTEM ICIV
VICTIM
(PA & antenna)
CULPRITS - - - COUPLING PATHS - - - - VICTIM
NOTE: SUBSYSTEMS ARE TAKEN TO BE COMPATIBLE WITH THEMSELVES
DESIGNING TO AVOID EMC PROBLEMS
227
Radiated susceptibility
has two components
I
I""
I
ConductedsuscepfibiJity
has on/yone component
"-
Av
w
Q.
en
Ac
Be
I-
~
a.
..J
:::>
Ce
<
en
en
Dc
ti
I
en
m
en
I
0
:e
w
)-.
:::>
I
I
Ne
Rs(E field)
Rs(H field)
SUE SYSTEMS AS VICTIMS (CS)
Bv
Cv
Dv
-I-~-"':""~ - -
""""
""""""
""
t
')
Each cell contains details of frequency,
level and modulation characteristics of
potential incompatibilities between
each combination of subsystems.
p'igure 12.5
\
'~l\
Susceptibilities divided into
CS • conducted susceptibility
Rs(E) - E field radiated susceptibility
Rs (H) - H field radiated susceptibility
Nv
""
{
~
~
i"---
The diagonal line represents
self-compatibility at subsystem
level.
Intrasystem compatibility matrix
considered to be potential culprits capable of
emitting unwanted electromagnetic energy by
conduction or radiation to other subsystems. The
rows in the matrix contain actual or estimated
susceptibility data for each subsystem/unit as a
victim of EM interference. The frequency and
amplitude details of any potential incompatibilities
between any subsystems/units are recorded in the
appropriate matrix elements.
For clarity, three rna trices can be used: one for
conducted interference incompatibilities and one
each for E- and H- field radiated incompatibili ties
as shown in Figure 12.5. The subsystems or units
are assumed to be self compatible and thus the
1:1 diagonal line in the matrix is void.
Many EMC system level programmes can be used
to 'cull' the many possible frequency matches which
will be found between culprits and victims, on the
basis of expected incompatibility level. Thus
potential subsystem incompatibilities can be
ranked into 60 dB problems, 30 dB problems or
relatively trivial problems of less than 10 dB. This
analysis can be very useful in directing the attention
of the design team to the key EMC issues at a very
early stage in the design. Detailed analysis of serious
incompatibilities can then be carried out with
computer models such as NEC [17J and EMAS
[18J or other finite element/difference/method of
moments or other electromagnetic codes.
Whatever computer software packages are used
to carry out system-level EMC assessments, a
great deal of reference data and a number of case
histories are usually used as background material
to support the current assessment. I t is therefore
important that the designers and managers of
projects with an EMC content, formally and
carefully, record data generated on their project
and make them available to future projects by
contributing to a company wide EMC database.
In recent years, some design teams have
attempted to codify EMC system and detailed
design knowledge in the form of EMC expert
systems which can be run on personal computers
[19, 20]. This technique may prove to be more
practical than the earlier large models and more
suitable as a tool for equipment designers rather
than EMC specialist engineers.
12.1.2.6 Test plan
The requirement for this document would be
written by the EMC project management team in
the case of a large project and would require the
designers and EMC test specialists to define what
testing is required at the various stages of the
equipment development. The plan itself would be
produced by the designers and EMC test
engineers. The test plan would include state,ments
on the following tests.
Risk reduction tests: These short tests would be
228
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
undertaken to resolve a design question in favour
of one technique or another. They are carried out
at a very early stage of the design and are in some
ways the most important tests which will be
carried ou t on the project. They will set the
course for all future EMC engineering solutions
and may be concerned with deciding on a
grounding and bonding philosophy or selecting
the types of integrated circuits to be used.
Development tests: These semiformal tests would
be required at certain well-defined stages of the
developing design to check that the EMI predictions
which will have been made are being achieved.
Such tests may be conducted before design drawings
are formally adopted and other elements of the
overall design are allowed to proceed on the basis of
what has already been achieved.
Occasionally additional informal development
tests may need to be conducted by the designer to
quickly verify the EMC benefits of a particular circuit, shield or technique. Such tests need not be done
by submitting the problem to a test house, external or
internal to the company. They are best done on the
bench by the designer responsible for that element of
the design who may be assisted by test personnel and
may need to use some of the specialist equipment
such as current probes and spectrum analysers.
Conformance tests: The test plan for these tests
is usually written by the EMC test laboratory
personnel in conjunction with the design team. It
requires intimate knowledge of the standards and
specifica tions which have to be met and the
limitations of test techniques which are specified.
In certain circumstances, on small projects for
example, a consultant may be called in to liaise
with the external approved test laboratory, to
help generate the test plan and to oversee the
testing which is carried out. The consultant may
also be in a position to advise the designer as to
the validity of the results obtained and to point
out improvements which should be made to the
design if the equipment has failed the test.
On large projects the certification testing may
involve formal demonstration of the equipment or
system functioning in its operational environment,
either at its place of installation or on a specially
prepared EMC test range. Often these final
proving trials are witnessed by a representative of
the customer's organisation and may be important
in obtaining a stage or final contract payment.
12.2 Systetn-Ievel EMC requiretnents
12.2.1 Top-level requirements
Depending on the nature of the product or system
and any specific clauses relating to EMC in the
contract to purchase, together with any EMC
legal obligations relating, to product sale, export
and use, the system-level EMC requirement can
range from simple to very complex. If complex, it
is necessary to consider a hierarchy of req uirements and define areas of precedence for certain
specifications and standards for the product as a
whole. For example, electrical safety requirements
are usually paramount.
Once the customer/contractual/legal/export/
licence for operation and electrical safety req uirements have been defined, it is then necessary to
estimate the probable levels of RF emissions and
susceptibilities of the proposed design. These data
can then be compared with the requirements, and
emissions reduction req uiremen t or hardening
requirement (for immunity) can be defined.
These EMI immunity hardening or emission
reduction requirements must then be apportioned
to the various subsystems such as power supplies,
mother board design, clock and processor circuits,
cable harnesses, interface boards/circuits and
mechanical design of the case or container, based
on the need to achieve these req uirements for the
minimum cost and impact on the optimum
equipment design.
12.2.2 Determining EMC hardening
requiremen t
The system hardening requirement for an
equipment which must meet a full range of interrelated electromagnetic specifications may have to
accommodate the following features.
EMC:
Transients:
NEMP:
Lightning:
Radiated susceptibility
Radiated emissions
Cond ucted susceptibili ty
Cond ucted emissions
Imported transient immunity
Exported transient generation
Radiated susceptibility
Cond ucted suscepti bility
Direct effect immuni ty
Indirect effect immunity
In addition, some equipments or systems may be
subject to extra requirements, such as that for
secure communications (Tempest). If all these
requirements have to be met simultaneously to
some degree, as for example with the modern
military aircraft, the task of reconciling the
differing technical solu tions to meet these req uirements can be considerable.
The generation of typical system hardening
requirements is demonstrated in what follows with
reference to radiated susceptibility and emissions.
When evaluating conducted emissions and susceptibilities the situation is more straightforward and
simple transmission-line models can be used.
DESIGNING TO AVOID EMC PROBLEMS
Large projects may use complex computer
models to define a system hardening requirement
given the specifications of the external electromagnetic environment and an estimate of the
internally generated interference. For most
projects, EMC systems engineers or designers can
use a number of simple models to yield a worstcase estimate of the hardening requirement. The
sophistication of the models available will depend
on the expertise of the design team and the
financial resources wi thin the project.
An example follows of the use of simple
modelling tools to establish an early estimate of
the scale of the EMC design task on a project.
Such information guides the technical and
management framework within which the electromagnetic design engineering of equipment is
carried ou t.
Consider Figure 12.6 which shows a system
EMC radiated immunity requirement for project
X. This will have been obtained from the EMC
standards and specifications called up in the
contract, with an additional element derived from
the engineering estimate of the potential interference levels likely to be self generated within the
equipment.
This
intrasystem
compatibility
requirement luay consider, for example, the local
fields due to high power RF radiation from an
antenna which may be associated with the
equipment being developed.
To calculate the hardening requirement it is
necessary to estimate the worst-case coupling from
the specified field to the equipment being designed.
Two features of the equipment tend to dominate
the EM field coupling: the length and type of cable
runs, and the characteristics of equipment boxes
and conductive structures in which they are
mounted together with any apertures, as shown in
Figure 12.7. A number of models can be used to
evaluate the worst-case coupling via the box and its
1000 . - - - - - - - - - - - - . . . . - - - - - - - - - - . - - - - - ,
E
>
100
30
:c
~
C)
z
w
a:
3
Cl
0.1
~
en
...J
COMPOSITE EXTERNAL
RF ENVIRONMENT
SPECIFICATION
W
u::
EXCURSIONS TO ACCOMMODATE
INTERNAL COMPATIBILITY (due to
radiating antennas in the system
for example)
I
COMPOSITE FIELD STRENGTH SPECIFICATION
1MHz
10MHz
100 MHz
1GHz
10GHz
FREQUENCY
Figure 12.6
Example of specification for composite RF
environment in which system must operate
229
CABLE
~---"" 7.5m 1 0 n g - - - - - !
------~:fj)
CURRENT INDUCED
IN CABLE
k
COMPLEX RF CURRENTS
HA/m
FLOWING IN BOX
....- - ~ - - ~ E VIm
STRUCTURE
Z (wave-
impedance)
--~--
FIELD INCIDENT
ON BOX AND CABLE
Figure 12.7
Example of box-and-cable pickup
apertures and a simple dipole model may be used
for field-to-wire coupling.
12.2.3 Simple coupling models
This section demonstrates how simple considerations of key physical aspects of a system, such as
its size and the length of conductors inside it, or
cables attached to it, can be used to predict its
coupling properties to external fields. Designers
working on projects which have access to sophisticated compu tel' models will of course make full
use of them, bu t they may also carry out calculations using simple models to crosscheck their
results.
Many examples of simple models exist [13, 14,
21, 22J which enable predictions of certain aspects
of EMI problems to be made. These include
Common-mode coupling of fields into the boxcable-box loop area for balanced and
unbalanced systems
Differential-mode coupling into box-cablebox loop area
Differential-mode coupling into coaxial cables
Capacitive coupling between circuits
Inductive coupling between circuits
Coupling rejection of twisted pair cables
Shielding effectiveness of coaxial cables
Shielding effectiveness of metallic screens
Filter performance models
Active component rectification models
Attenuation of EM waves through buildings.
The selection and combination of these simple
models to 'scope' EMI problems in a system
req uires experience. Methodologies derived by
White [22J and implemented in the form of
computer software can be of assistance. As
examples of simple models, the circuits on which
the capacitive and inductive coupling models are
based are shown in Figure 12.8. The field -to-cable
common-mode coupling circuit is shown in Figure
230
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
EM wave couples
into loop area
(Received
noise)
(Source of
noise/EMI)
Cross talk capacitance
s
(Source of
noise/EMI)
"---~~--~--Mutual
impedance
COMMON-MODE COUPLING INTO BOX-CABLE-BOX-GROUND LOOP AREA
Ico
-10---r----r----r--_-....--
_
-20
"0
Figure 12.8
for f
-;
1
)
1 + J wCcv < vlm
=
0..
-50
8
-60
w
o
o
:E
Z
o
:E
:E
o()
wCw<zlm
« 1/2nCcv < zlm
where
2nfxfrequency in Hz
Cev
wire-to-wire coupling capacitance per
metre
< v = parallel combination of victim source and
load impedances and wiring capacitance
Cv to ground = l/(1/<vI + 1/ <v2
+ jwCvlm)
lm = cable length in metres
Cv = victim wire capacitance to ground return
per metre
( b) Circuit representation of inductive coupling
between parallel wires over ground plane
W
-40
:::>
( a) Circuit representation of capacitive coupling
between parallel wires over ground plane
= (
-30
~
::J
(b)
Typical equivalent circuits used to model
cable crosstalk above ground plane
Vv/Vc
~
=
=
Reprod ueed by permission of I CT Inc.
12.9 together with examples of the calculated
coupIing response for various loop areas as a
function of freq uency.
Engineers at McDonnell Douglas [21] have
cond ucted many experiments on field -to-wire
coupling of representative avionics cables, including
single wires. They showed that the coupled power
from the field to the conductor depended on
wavefield frequency
wire orientation to the wave
wire geometrical factors: length, dialueter,
shape, rou ting
terminating load impedance
In a real system there is little control over the
routing and orientation of cables with respect to
any particular subsystem and the internal field-tocable coupling can be considered as random.
Measurements made by McDonnell Douglas using
different lengths of cable and load impedances
Figure 12.9
Two-box EMI problem
Reprod uced by permission of ICT Inc.
showed little effect on the pickup probability distribution function, which has a log-normal form with
a standard deviation of between 3 and 6 dB.
Shielded wires of course will normally tend to
pick up less than unshielded wires, but the distribution means may not be as widely spaced as the
assumed shielding figure (of perhaps 30 dB) would
suggest. Practical measurements of real cables
with imperfect shield terminations, poor braids
etc, show that the worst-case pickup from a
shielded cable can be comparable with pickup
levels for an unshielded cable. See Figure 12.10.
cF-
SHIELDED WIRE
PICK-UP PROBABILITY
DISTRIBUTION FUNCTION
difference in means corresponds
to 'average shield performance'
) I
(
w
o
zW
14-----'----
UNSHIELDED WIRE
PICK-UP PROBABILITY
.-/ DISTRIBUTION FUNCTION
0:
0:
::::>
o
o
o
LL
o
~
co
«
CD
o
0:
_ _----1......_ - - 1
O'~_~
I0000-~.......~ - -..........~
Overlap in distributions indicates that occasionally pick-up
in a shielded wire is as great as in an unshielded one.
Figure 12.10
Probability density functions for shielded
and unshielded wires
Reprod ueed by permission of McDonnell Douglas
DESIGNING TO AVOID EMC PROBLEMS
O~----------,r--------.....,.
i-wave
w
cr::
....
cr::.....,
:,)
dipole aperture = 0.131..'
Maximum power induced
at close to first cable or
structure resonance
·10
"
~..s .20
~3:
OCO
~§
-30
~
·40
0:::"0
LLO
a......J
LL
It,.-o
~
:::>~
OLL
.. ·0.16 m long wires
• - 3.05 m long wires
0.1
""'"
dipole model
1
10
3:0
~~
0:::
Measured maximum effective apertures
( A e ) of various wire lengths. The halfwave dipole is a reasonable upper bound
for these experimental data
,,
i
I
I
2
Intercept point at close to
first cable or structure
resonance
Pa
..!..
f2
Pa ')..}
~20 dB / decade I
2
LL-
FREQUENCY GHz
Figure 12.11
UJUJ
"
Electrically short
mismatched
Paf
Pa 1
O:::z
--I
"
UJUJ
a.....-
~ cable, or system structure.
--------·1
-3:
5~
-50~
cable/structure
is electrically
short
I
cable/structure
is approximately
resonant
cable/structure
is electrically
long
1....- - - -
0.1 MHz
1MHz
10MHz
100MHz
FREQUENCY
1GHz
10GHz
close to first cable or structure resonance
typically 5 - 50 MHz for average system
Reproduced by permission of McDonnell Douglas
The McDonnell study showed that the pickup
could be characterised by calculating the effective
aperture of the wire by dividing the power picked
up and delivered to the load by the wavefield
power density:
Figure 12.12
12.1
where P == power picked up by the wire (watts),
P d == EM-field power density (W/m 2 ), and
A e == effective aperture of the wire (m 2 ).
Measurements of the maximum effective aperture
of real wires produces a plot as shown in Figure
12.11 for which a least squares fit is close to that
for the theoretical aperture for a matched
halfwave dipole, which is given by
12.2
where A == wavelength. This matched-dipole
formula is not, however, useful at low frequencies
where the length of a halfwave dipole would be
greater than the actual length of any cable or
system structure. Thus the resonant matcheddipole model should be abandoned at frequencies
much below the fundamental cable or system
structure resonance.
A t such frequencies the condition for a tuned
halfwave dipole is not physically achievable in the
real system and the model dipole becomes
detuned and electrically short, with a rising
reactive source impedance still driving the fixed
load impedance. Under these conditions the
power delivered to the load tends to fall with
freq uency owing to the mismatch [13, 21].
From the McDonnell Douglas study two things
may be deduced:
(i)
Coupling for matched dipole (tuned length) is
unrealistic below first resonance length of
"
We;'
~.!
231
Complex coupling in real systems is best
treated in a statistical fashion without
(ii)
Composite wavefield to structure/cable
model: inverted V
making an attempt to calculate individual
coupling path coefficients for the enormous
number of possible coupling combinations.
The exception to this approach arises when
there is a clear dominant coupling path
from a strong interference culprit to a
sensitive victim subsystem. In such a case
the coupling to the particular cable should
be calculated individually.
The simple matched dipole formula can be
used to crudely estimate the worst-case fieldto-cable coupling. For frequencies below the
cable first resonance a limit must be applied
to the matched dipole model and a roll off
with frequency can be used resulting in the
combined curve appearing as an inverted-V
as shown in Figure 12.12.
12.2.4 Susceptibility hardening case study
12.2.4.1 Cable hardening requirement
Consider the equipment shown in Figure 12.7 with
a box of electronics of 1 m side connected to an
unshielded cable approximately 7.5 m long, which
will have its first resonance in the region of
20 MHz. Let the specified RF field strength in
which this equipment must operate be as shown
in Figure 12.6 and reproduced as curve A in
Figure 12.13. As an example of a general
coupling model, use the simple matched-dipole
worst-case pickup model at frequencies where the
cable is electrically long (above 20 MHz). One
can estimate the induced power shown in Figure
12.13 as curve B (shown dashed above 1 GHz).
The coupled power at low frequencies rolls off
232
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
z
Figure 12.13 Development of
cable hardening equipment
o
:r:~
""0
0
-
Z~
ClUJ 0
...Ja:w
~ .... a.
U-(J)CJ)
1000 VIm
10 VIm
1 VIm
30
CURVE IB I
20
/
10
~"0
0
,.,..BURN
....... --OUT ( linear & digital
g, -10
... --'1'"
/
~
() -20
c::
ffi
-30
~
-40
0..
-50
-60
-70
----
... --------
---... -~----""
. .-
I, ~CMOS
~
• • TTL
•
~
integrated circuits )
~
~
CMOS DEVICES_ ~
(leVelchange)~
TTL DEViCES. . .
• _. --
------/--(Ievelchange)
........ ~
~L1N IC
~
~.
-
.~
CURVE'E'~
_./
_ - - - .....
LINEAR ICs
z
~o m~
CURVE 101
:::>
10dB
~
fZ
w
0
~
UJ
...J
SYSTEM CABLES
~
w co
c:: "0
5
aw 80
c::
'20dB
«CO
()
SIMPLE WORST CASE HARDENING REQUIREMENT
70
z
Z 60
w
0
c::
«
50
:c 40
w
...J
CD 30
«
0
~
w
....
CJ)
>-
CJ)
20
10
0
1 MHz
with frequency from the value at 20 MHz (close to
the first cable or structural resonance). Applying
this roll off to the specified field strength (curve A)
in this frequency range generates curve C. Because
the system power and data cables in which the
pickup is occurring are not specially designed to
transfer RF signals, there is an additional cable
loss above 1 GHz which should be introduced as
shown in curve D. This modifies the pickup (curve
B) above 1 GHz and results in curve E. The final
simple estimate of maximum power picked up in
the cable and delivered to circuit (loads) inside the
box is given by curves C and E.
10 MHz
100 MHz
FREQUENCY
10Hz
100Hz
For specific system configurations, other simple
coupling models, such as the box-cable-box model
(referred to earlier [22J) may be appropriate and
can be used in a similar vvay to predict the power
extracted from a field and delivered to a
potentially susceptible circuit in the box.
The delivered power may now be compared
with susceptibility levels for the active electronic
devices used in the equipment to yield the
hardening req uiremen t.
Various susceptibility levels can be de.fined for
different types of active device such as linear
bipolar ICs, linear MOSFET's, TTL logic,
DESIGNING TO AVOID EMC PROBLEMS
CMOS logic etc. [21 J. These are shown as the
family of dotted/dashed lines in Figure 12.13. A
composite worst-case curve could be produced for
all IC types used in the equipment, for both
functional upset and circuit damage. This could
then be used to generate the hardening
requirement by comparison with the pickup
power.
In this example the most severe susceptibility
curve for linear I Cs has been chosen and
subtracted from the power pickup curve (C and
E)
to give the system cable hardening
requirement which is the lower curve in Figure
12.13.
12 ~ 2.4.2 Equipmen t case hardening
req uiremen t
The process that is undertaken to derive the
approximate worst-case hardening requirement
for the equipment case (Figure 12.7) is similar to
that for generating the cable hardening
requirement. The fundamental simple model will
of course be based on the screening performance
of the case material [13, 22J. However,
penetration through a well constructed metal
case will be dominated by leakage through
joints, slits and other intended apertures.
Microwave EM energy will radiate through
suitably
sized
apertures
directly
to
the
susceptible device and associated wiring/PCB
tracks. The transmission of radiation through
shield imperfections can be modelled as
waveguide apertures or slot antennas.
The preceding example illustrates the use of
simple approximations to quickly assess the level
of EM C design required for a particular
equipment which helps to direct early design
effort to where it is most needed.
12.2.5 Emission suppression requirement
The foregoing has demonstrated how simple
considerations can lead to a rough assessment of a
system hardening requirement for system susceptibili ty. Similar considerations of voltage swings
and current flows generated by active components
around circuit board conductors can lead to an
estimate of the likely radiated signal strength from
the equipment at a particular distance (which
may be that stated in the emission standards, say
1, 3, 10 or 30 m). A rough spectrum of the signals
generated by digital and other circuits can
quickly be estimated from their waveforms by
using Fourier transforms or transform look-u p
tables.
It must be emphasised that these techniques are
only a rough guide to setting the system
233
hardening and suppression requirements. Some
designers will have access to more sophisticated
computer models which will lead to a more
detailed understanding. For those who do not
have these software tools, the approach outlined
here may be useful in demonstrating that some
progress may still be made.
12.2.6 System hardening flow diagram
A process for deriving a set of EMC system
hardening requirements is summarised in Figure
12.14 where a simple flow chart is presented. A
key decision to be made during the process is
when to cease calculation and to begin
preliminary assessment testing in order to further
reduce the engineering risk in the EMC design.
A general rule of thumb is based on the
hardening requirement being greater or less than
30 dB. If the initial calculations indicate that the
EMC hardening or suppression required is less
than 30 dB, further calculation effort to refine the
estimate may not be as useful as a quick and
simple test. The simple calculations are generally
only accurate to about 10-20 dB and the tests
should be made to generate information about the
actual pickup or emission levels within the system.
(Bear in mind that these measurements will also
be subject to some uncertainty.) However, the
extra practical information will undoubtedly help
to guide the design process.
If the initial system-level calculations show a
hardening requirement greater than 30 dB the
engineering design on which they are based
should be re-examined and various mitigation
approaches involving specific design features
should be tried until the hardening requirement is
closer to 30 dB. If the calculations show that the
hardening requirement is close to zero, then to
save development time it may be worth risking
the cost of a system or preconformance test
against the specified requirement.
12.2.7 Subsystem apportionment and
balanced hardening
Once the system hardening requirement has been
established for radiated emissions, susceptibility,
conducted interference and transients, it is then
necessary to apportion the overall requirement
down to subsystem or uni t level. The details will
be specific to the system in question and the task
is not necessarily an easy one. Success relies
heavily on the experience of previous design cases,
and expert system software which incorporates
this knowledge can be of help here.
EMC is achieved through a number of technical
measures applied at various levels from component
234
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
Figure 12.14 Typical
hardening task flow chart
for system susceptibility
.....-----4
YES
YES
SYSTEM
DESIGN
INPUTS
PICK UP
LEVEL
known?
HANDBOOK
coupling information
or expert system
HANDBOOK
Component
susceptibility
information or
expert EMC
system
Perform more
detailed
VULNERABILITY
ANALYSIS
COUPLING
MODELS
greater than 30 dB
( usual case)
Refine
SYSTEM
HARDENING
REQUIREMENT
Determine.
HARDENING
REQUIREMENT
less than 0 dB
( rarely achievable)
( sometimes achieved)
detailed
DESIGN
TECHNIQUES
& MODELS
Reproduced by permission
or BAe Dynamics Ltd.
selection and positioning on a circuit board up to
efficient global shielding, for example afforded by
a metallised plastic case which might surround a
personal computer. For cost-effective EMC
measures which meet the system hardening
requirement without
reducing
the system
functional performance, balanced hardening is
necessary. This req uires careful selective apportionment of the EMC requirements for each
electronics box, unit or subsystem, including the
cabling design/installation and the mechanical
design of the hard ware boxes and vehicle or
system structure.
The apportionment must be made on the
grounds of what is technically achievable for an
affordable cost based on using complementary
EMC design techniques at the various levels of
construction. Table 12.1 indicates some of these
techniques and the levels at which they can be
applied.
Often an effective hardening programme
requires a careful combination of screening,
filtering, grounding, bonding, isolating, frequency
planning and component selection. Generally the
techniques must be used together if they are to be
effective at all levels where they are employed.
For example, there is no point in placing a noisy
circuit in a well-designed screened box if the
input and output cables are not filtered to the
same standard. Equally, one would not allow a
high-power RF transmitter to operate at a
frequency which was known to be in-band to
other equipment in the system which is sensitive
to that frequency. Bandpass filters would be used
at the Tx and Rx subsystem ports in conjunction
with frequency planning to minimise unwanted
interference.
EMC techniques such as these must be
employed in a coordinated way across the whole
system being designed. The process should be
under the direction of the chief designer who
controls and monitors the EMC tasks from
component selection to the final system test to
achieve the best EMC performance for the
minimum cost, weight, space and impact on
system reliability and maintainability.
DESIGNING TO AVOID EMC PROBLEMS
235
Table 12.1 EMC hardening techniques
EMC technique
Applied at
EMC technique
Applied at
Component selection
Circuit level
I C type selection
Component placement
Component screening
Component filterIng
Component-case grounding
Spectrum limiting: fast-edge slugging
Use high signal levels for good noise
immunity
Frequency management: selecting
oscillator, Tx, Rx, IF, frequencies
etc.
Use low-power circuits where
possible - for low emissions
Bandlimit RF inputs and outputs to
minimise spurious, intermod. and
overload signals
Screened power and signal cables
Subsystem level
Use lossy filter line
Subsystem grounding and bonding
plan
Cable routing: minimise cable runs
and loops
Cable grounding scheme: single
point, both ends, multiground
Use isolated power supply
Positioning of subsystem components
on structure
Use differen tial interfaces
Use signal ground reference
Transformer couple
Use optoisolators on key interface
lines
Employ fibre optic signalling
Large RF ground plane
Use RF layout techniques for
digi tal boards
Minimise track loop area
Minimise HF signal current
Employ loop-area compensation
Close mounting of ICs to PCB
Use of surface mount components
Decoupling chip capacitors
Board grounding
Board edge/section filtering: with
chip capacitors or lossy ferrites/
pastes
Use global shield
System level
Ensure all structure components are
bonded
Minimise structure penetrations
Use waveguide beyond cutoff
access ducts
Employ correct RF gaskets
Use system grounding plan
Use single RF ground if appropriate
Board level
Screened box with minimum
Box level
apertures
Box with RF compartments
Use of RF gaskets
Screened cables
Cables not routed in corners of box
or behind slots and apertures
Board ground planes well-grounded
to box
Box grounded to structure
Fil tered connectors
Connectors with 360 0 backshells for
shield termination
No unfiltered cable penetrations
12.2.8 Staff support for EMC
The design, manufacture, and field service personnel
all have a role to play in ensuring successful EMC of
a product. I t is not just the responsibility of the
electrical designer and his immediate team. The
Break u p electrically resonant
structures
Use RAM or lossy coatings
Cover windows, air vents etc. with
suitable RF screening
Minimise exposure to external high
power RF fields during operation
Site equipment away from sensitive
receIvers
mechanical engineers, wiremen, installers and
service teams must all contribute. This will
necessitate these staff having an understanding of
what EMC is and how it is achieved and maintained.
Many company managements are unprepared for
this aspect of meeting the EMC requirements which
236
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
are increasingly being placed on their products
through measures such as the EC Directive 89/336 on
EMC. It is probable that proper EMC training for
each type of staff involved in designing and supporting eq uipment will be necessary in the future.
Prospective EMC engineers should ensure that they
receive professional training before engaging in this
fascina ting bu t sometimes difficult engineering field.
12.3 Specific EMC design techniques
This book is concerned primarily with EMC
testing; the higher level aspects of product or
system design to meet EMC requirements have
been discussed in some detail so that the reader
can appreciate the nature of the overall EMC
design task. This clearly involves more than
specifying a mains filter connector, fitting a few
chip capacitors on a PC board, or spraying the
inside of the plastic equipment case with metal. It
is not the intention to detail all the techniques
mentioned for achieving good EMC or to give the
basic formulas that would be needed to enable a
design. Many other books and papers have been
written [8, 11-15J on the whole range of design
techniques and it is suggested that these and other
references are consulted for information on the
following topics:
Shielding theory [8, 13, 14, 23, 24J
Surface transfer impedance [25 J
Cable screening design [8, 13J
Cable crosstalk coupling, capacitive and
ind uctive [8J
Transmission line theory [26J
Filters, types and application [8, 13, 14J
RF grounding and bonding [8, 13, 14J
Corrosion control of bonds [23, 24J
Gasketting [13, 14,23, 24J
Frequency planning [8J
PCB design [8, 27-33J
Many of the references cover more EMC design
topics than are listed. The books and papers
themselves also have extensive references and
bibliographies. With these it should be possible
for the reader to begin to explore the full range of
EMC design techniques and their applications.
12.4 References
HILLARD, D.E. et al.: 'Social and economic implications of EMC: A broadened perspective'.
Proceedings of IEEE symposium on EMC, 1990,
pp. 520-525
2 OTT, H.W.: 'EMC education - the missing link'.
Proceedings of IEEE symposium on EMC, 1981,
pp. 359-361
3 PEREZ, R.J.: 'First year graduate level course In
Electromagnetic compatibility'. Proceedings of
IEEE symposium on EMC, 1990, pp. 232-239
4 RILEY, N.G. et al.: 'A university post-graduate
course in EMC'. Proceedings of IEEE symposium
onEMC, 1990, pp. 240-242
5 HERIMAN, D.H.: 'Education and training of the
industrial regulatory compliance test team'.
Proceedings of IEEE symposium on EMC, 1981,
pp. 365-368
6 'A structured design methodology for control of
EMI
characteristics'.
Presented
at
IEEE
symposium on EMC, 1990 (late submission)
7 SULTAN, M.F. et al.: 'System level approach for
automotive
electromagnetic
compatibility'.
Proceedings of IEEE symposium on EMC, 1987,
pp. 510-520
8 WHITE, D.R.J. and MARDIGUIAN, M.: 'E1\I1I
control methodology and procedures'. ICT ISBN
0-944916-08-2
9 NAVAIR AD1115 (obsolete but very useful).
Department of Defense, Washington DC, USA
10 NWS 1000, part 1. Ministry of Defence, UK. Chap.
5, section 10
11 'Electromagnetic compatibility design handbook'.
US airforce systems command, 1975, DR 1-4
12 'Electromagnetic (radiated) environment considerations for design and procurement of electrical and
electronics equiprnent'. MIL-HDBK-235, DoD,
Washington DC, USA, june 1972
13 KEISER, B.: 'Principles of electromagnetic compatibility'. (Artech House, 3rd edn.)
14 DUFF, W.G.: 'Fundamentals of electromagnetic
compatibility'. Interference Control Technologies,
Inc, Gainesville, Virginia, USA
15 'The achievement of electromagnetic campati bili ty' .
Report 90-0106, ERA Technology, Leatherhead,
Surrey, LT22 7SA, UK
16 JOHNSON, W.R., COOPERSTEIN, B.D. and
THOMAS, A.K.: 'Development of a space
vehicle electromagnetic interference Icom pati bili ty
specification'. NASA contract 9-7305, final
engineering report document 08900-6001-TOOO,
TRW systems, Redondo Beach, CA, USA, june
1968
17 BURKE, G.J. and POGGIO, A.J.: 'NEC-2
numerical electromagnetics code Method of
moments: A user-oriented computer code for the
analysis of the electromagnetic response of antennas
and other metal structures'. NAVELEX 3041,
Washington, DC 20360, USA
18 'EMAS
electromagnetic
code'.
MacNealSchwendler Co Ltd, 85 High 81., Walton on
Thames, Surrey KT12 IDL, UK
19 PRICE, M.J.S. and MACDIARMID, I.P.:
'Developing an expert system for EMC design'.
Proceedings of IEEE symposium on EMC, 1988,
pp. 331-336
20 LOVERTI,j. and PODGORSKI, A.S.: Evaluation
of HardSys: A simple EMI expert system'.
Proceedings of IEEE symposium on EMC, 1990,
pp. 228-232
21 'Integrated circuit electromagnetic susceptibility
handbook'. Report MDC E]929, phase 3,
DESIGNING TO AVOID EMC PROBLEMS
22
23
24
25
26
27
McDonnel Douglas Astronautics Company, St
Louis, Missouri 63166, USA
WHITE, D.: 'Montreux workshop on applications
of programmable calculators and minicomputers
for solutions of EMI problems'. Don White
Consultants
Inc.,
14800
Springfield
Rd.,
Germantown, MD 20767, USA
'Design guide to the selection and application of
EMI shielding materials'. Tecknit EMI Shielding
Products, Cranford, NJ 07016, USA, 1982
'EMI shielding engineering handbook'. Chomerics
Europe, Globe Park Industrial Estate, Marlow,
Bucks SL7 lYA, UK, Jan. 1987
RICKETTS,
L.W.,
BRIDGES,
J.F.
and
MILLETTA, J.: 'EMP radiation and protective
techniques'. (Wiley)
SMITI-I, A.A.: 'Coupling of external electromagnetic field to transmission lines'. (Wiley)
VIOLETTE, M.F. and VIOLETTE, J.L.N.: 'EMI
con trol in the design and layou t of printed circuit
28
29
30
31
32
33
237
boards'. EMC Technol.) l\1arch-April 1986, pp. 1932
MARDIGUIAN, M. and WHITE, D.: 'Printed
circuit board trace radiation and its control'. EMC
Technol. Oct. 1982, pp. 75-77
MARDIGUIAN, M.: 'Prediction of EMI radiation
from PCBs', R F Design, July/August 1983, pp. 2636
KOZLOWSKI, R.: 'Follow PC board design
guidelines for lowest CMOS EMI radiation'. EDN)
May 1984, pp. 149-154
COOPERSTEIN, B.: 'Radiation from printed
wiring boards'. Xerox Corporation, 701 S Aviation
Blvd. El Segundo, CA 90245, USA
WAKEMAN, L.: 'Transmission line effects
influence high speed CMOS'. EDN, June, 1984,
pp.171-177
POLTZ, J. and WEXLER, A.: 'Transmission line
analysis of PC boards, VLSI Syst. Des., March
1986, pp. 38-43
Chapter 13
Achieving product EMC: checklists for
product development and testing
13.1 Introduction
In the last few years, with more market growth
in prospect. The existence of this large market
su pports the choice of the personal com pu ter
(PC) as a good example with which to consider
the task of coping with EMC product
development for the first time. The general issues
addressed will also apply to manufacturers of
other electronic products including industrial,
scien tific and medical eq uipmen t and household
electrical/electronic appliances. The specifications
and details of test methods however will be
differen t for each class of products as has been
pointed out in the preceding chapters.
13.1.1 Chapter structure
This chapter is written as a set of checklists in the
form of flow diagrams which engineers and
managers can use to assist in generating their own
EMC product development and test programiues.
It highlights the importance of the issues
previously discussed and relates them in terms of
an overall EMC programme.
13.1.2 Example adopted
To focus the discussion, assume the point of view of
a manager in an electronics company manufacturing personal or small business computers who
has recently heard about EMC and the possibility
of the European Harmonisation Directive having
some impact on the company's business. Assume
that the manager has no particular background
in electromagnetic engineering, and that there is
no one to turn to in the company who has direct
experience of EMC.
The issues that would need to be considered are
dealt with in the form of a top-down appraisal,
starting with general questions such as 'What is
EMC and how does it affect my operation?'
(including assessment of relevant standards).
Consideration is also given to the issues involved
in setting up an in-house test facility to self certify
new products. Specifically, the discussion centres
on the following broad issues:
13.2 Inform.ation about EMC
Managers and engineers need information on a
number of aspects of EMC to plan and properly
execute a product development and certification
programme. A check list of possible useful sources
of information follows.
13.2.1 Customer sources
The primary motivation for a manager In an
electronics company to understand EMC is the
need to meet the expectations of his customers. In
turn, their needs may be driven by regulatory
authorities which implement national or international legislation on EMC. Manufacturers can
only sell and customers will usually only buy
products which meet the requirements of the
regula tory au thori ty, and in that sense the
regulations are the main driver. Customers may
also have requirements for aspects of EMC which
are not covered by mandatory government
regulation. For example, enforceable regulations
covering PCs and other IT products in some
countries may only relate to their EM emission
performance, but the customer/operator may also
be concerned about reliable operation in a hostile
RF environment and thus be interested in
equipment performance with respect to radiated
or conducted susceptibility
Among the first questions the product
development manager must ask are:
Where to obtain information about EMC
Determining EMC requirements for new
products
Developing an approach to EMC design
Setting up an in-house test facility
13.1.3 Personal computers and
information technology
Personal/business computer products represent a
large part of the electronics ind ustry and
choosing this relevant example permits the
discussion of EMC issues to be focused for
increased clarity. The sales of such equipments
into the home and office have increased rapidly
238
Who are my main customers?
Which countries are they in?
ACHIEVING PRODUCT EMC: CHECKLISTS FOR PRODUCT DEVELOPMENT AND TESTING
Do my customers demand EMC performance?
Are their requirements legislation driven?
Are their requirements operationally driven?
Do they demand special EMC performance
which it would be uneconomic to provide in
tha t sector of the market?
The information gained will lead to a number of
specifications being cited depending on the
product type and customer countries. For
example, to sell worldwide, the PC manufacturer
may have to meet the requirements of
FCC part 15j (RF emissions) + voluntary
immunity standards for USA customers
VCCI (RF emissions) + any special voluntary
immunity standards for customers in Japan
EN 55022 (RF emissions) for customers in Europe
EN 55101-2 Immunity to ESD
EN 55101-3/4 Immunity to radiated and conducted
EMI for customers in Europe
There may also be specific single customer EMC
requirements which must be taken into account if
the manufacturer sells high-cost customised
systems.
In consultation with the legal and sales and
marketing departments, the example product
manager in the PC company must attempt to
draw up a precedence hierarchy for EMC specifications which are to be met by the new product,
depending on volume sold, technical difficulty of
compliance, plans for future market, competitors'
EMC policy, etc.
13.2.2 Regulatory authorities
The specifications cited will be contained within
EMC standards produced by various bodies such
as the CENELEC, IEC, CISPR,VDE, BSI,
SAE, IEEE, etc and called up by the clauses in
the appropriate regulations. In the UK, the DTI
Radiocommunications Division is the responsible
legislative authority and produces papers for
guidance on EMC [1--4]. 1'he Department have
an active awareness campaign (1993 onwards)
designed to provide industry with a great deal of
technical information on EMC. At the time of
preparing this text information can be obtained
from
DTI
Implementation and interpretation
of regula tions
Manufacturing Technology Division
Department of Trade and Industry, Room 1/112
151 Buckingham Palace Road
London SW1 W99SS
o17 1 2 15 1403.
239
Notified bodies
Appointed by the DTI and operate the type
examination procedure on their behalf for certain
classes of equipment e.g. radio transmitters
Radiocommunications Agency, Room 106
Waterloo Bridge House
Waterloo Road
London SE 1 3UA
0171 215 2084
concerning RF matters
DRA
ARE Fraser Ranger
Fort Cumberland Road
Eastney
Portsmouth P04 9LJ
Air Traffic Service Standards
Aviation House
Gatwick Airport
Gatwick
West Sussex RH6 OYR
Other sources:
Contact point for type approval of radio transmitters:
Radiocommunications Agency, Room 514A
Waterloo Bridge House
Waterloo Road
London SE1 8UA
For copies of the EC directive
Alan Armstrong Ltd
2 Arkwright Road
Reading RG2 OSQ
01734 751771
Progress on harmonised standards
BSI
2 Park Street
London W 1A 2BS
0171 629 9000
BSI Standards Sales Dept.
BSI
Linford Wood
Milton Keynes MK14 6LE
01908 221 166
Technical help to exporters
BSI Standards
01908 226 888
For information relating to the EC commiSSion
contact the London office: Tel. 0171 222 8122
For information relating to the European
Parliament contact the London office: 0171 2220411
240
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
Information relating to EMC quality assurance
and laboratory accreditation in the UK can be
obtained from
NAMAS
National Physical Laboratory
Teddington
Middlesex
TW110LW
0181 943 7140
0181 943 7094
Information is also available concerning RF
measurements and calibration of EMC antennas
from
Division of Electrical Science
National Physical Laboratory
0181 943 7175
For details of services and staff at NPL consult
Reference 5
EMC contacts for military equipments are usually
arranged through MOD PE for the specific
equipment in question. Helpful advice can usually
be obtained from
Dr N Carter, Mission Management 5
RAE Farnborough
Hants, GU14 6TD
particularly on matters relating to aircraft. A list of
US EMC contacts for military systems is given in
the ITEM handbooks (see 13.2.7).
13.2. 3 Industry sources
Information on EMC matters can be obtained
from trade associations. In the example of a PC
manufacturer
this
would
include
ECMA
(European Computer Manufacturers Association).
ECMA
Rue DuRhone 114
CH-1204 Geneva
Switzerland
22-353634
Association of the Electronics,
Telecommunications and Business Equipment
Industries (EEA)
8 Leicester Street
London WC2H 7BN
0171 437 0678
Information on EMC standards, design techniques
and testing is also available from
ERA Technology Ltd
Cleeve Road
Leatherhead
Surrey KT22 7SA
01372 374151
ERA have produced 'Guidelines
international recommendations
relating to EMC' presented at a
exhibition 'EMC 91
direct
Feb. 1991
to national and
and standards
conference and
to compliance',
Manufacturers with an interest in Civil Aircraft
Avionics can contact the EMC Club,
Secretary D.A. Bull,
RAE Farnborough
Mission Management 5
Hants, GU14 6TD
Most NAMAS-approved EMC test houses will
give advice on standards, design techniques and
testing. A list of such facilities can be found in the
NAMAS M3 document [6] and in Appendix 13.1
Competent Bodies will also offer advice on EMC
design and testing to meet the EC Directive, a list
is provided in Appendix 13.2
A list of over 40 organisations offering EMC test
or consultancy services can be found in a special
EMC edition of New Electronics [7].
13.2.4 Equipment, component and
su bsystem suppliers
There are a large number of EMC equipment
suppliers for everything from screened rooms to
spectrum analysers; they can be helpful with
general information which need not be strictly
related to their products. They are often among
the first to appreciate the impact within the
electronics industry of new EMC legislation or
test methods. If one particular person does not
know the answer to a question, they will often
know of a contact who does. Any product
manager or manager setting up an EMC test
facility will find the representatives of equipment
suppliers a good source of information on EMC
matters. An efficient way to make contact with
firms is to attend one of the national/international
EMC conferences and exhibitions which are held
in most years. Electronic component and
subsystem suppliers may also be helpful in
providing specific product information if their
goods
have
been
designed
with
EMC
performance in mind.
13.2.5 Professional bodies and
conferences
'The lEE and IEEE regularly sponsor national and
international conferences on EMC. They are well
worth
attending
and
valuable
conference
proceedings are published, usually quite quickly
after the event. 'The IEEE also produce a
specialist journal of their transactions on EMC.
ACHIEVING PRODUCT EMC: CHECKLISTS FOR PRODUCT DEVELOPMENT AND TESl'ING
The Electromagnetic Compatibility Society of the
IEEE is designated S-27 and ,has its headquarters
at
345 East 47th Street
New York, NY 10017, USA
The lEE
Electronics Division
Technical Information Unit
Savoy Place
London WC2R OBL
o171 240 187 1
The Society of Automotive Engineers has an EMC
committee designated AE-4 with headquarters at
400 Commonwealth Drive
Warrendale, PA 15096, USA
The Electronic Industries Association have an
EMC committee (G-46) at
2001 I Street, NW
Washington, DC 20006, USA
The dB Society is a special organisation for persons
with considerable experience in the field of EMC.
It is a worldwide organisation and the contact
point in the UK is at
Mission Managemen t 5
Room 302, Q153 Building
RAE Farnborough
Hants, GU14 6TD
13.2.6 EMC consultants and training
Information available from EMC consultants can
be extensive, but is rarely free. There are a
growing number of consultancy organisations
within the UK and they can usually be found
through company and trade directories. Some
individual consultants, including those within
companies, may be contacted through
The Association of Consulting Scientists
11 Rosemont Road
London NW3 6NG
0171 794 2433
A number of companies offering EMC consultancy
are listed in Reference 7, with about an additional
30 offering consultancy along with other EMC
services. Using a consultant is a quick way to gain
initial EMC information about legislation,
standards, design techniques and testing. It may be
expensive and a manufacturer who takes EMC
seriously for the long term competitiveness of his
business will probably wish to develop some inhouse capability. Consultants can still be brought
in as needed, to assist the in-house team in tackling
241
a particularly difficult EMC problem, or venturing
into a new market with its own EMC requirements.
A list of organisations offering consultancy and
training in EMC is given in Appendix 3.3
13.2.7 Electronics and EMC technical
press
There are a number of specialist EMC publications and a few periodicals which have a special
interest in EMC. Among these are
ITEM,
Interference Technology Engineers'
Master, directory and design guide for the con trol
of EMI. Published by Robar Industries, Inc.
R & B Enterprises Division
20 Clipper Road
West Cosnshohocken
PA 19428-2721
USA
EMC Technology, Published by Don White,
Interference Control Technologies
5615 West Cermack Road
Cicero, IL 60650-2290, USA
New Electronics
Franks Hall
Horton Kirby
Dartford
Kent DA4 9LL
DTI EMC awareness campaign
EMC helpline (1993) 0161 954 0954
Managed by Findlay Publications
EMC Awareness Campaign Administrator
Findlay Publications
Franks Hall
Horton Kirby
Kent DA4 9LL
A list of useful publications (available 1993)
related to EMC is given in Appendix 3.4.
13.3 Detertnining an EMC
requiretnent
Consider again the example of a PC manufacturer
who has just realised that EMC exists and that it
will probably apply to his future products but has
no experience and no contacts in the field of
EMC. The broad questions that should be
considered were listed briefly in paragraph 13.2.1;
these are now examined in the framework of a
logical flowchart which will act as a checklist to
enable the 'PC product manager' to get started in
defining the system level EMC requirement for a
new product.
242
A HANDBOOK FOR EMC TESTING·AND MEASUREMENT
Any specific
EMC requirements based
on operational environment
_____
Customer's stated
EMC requirements
.......- - - - 1
EMC standards/legislation
relating to product type or
country.
(Mainly for emissions)
t
t
Immunity to RF ESD, lightning
& faults on mains power lines/
transients - leads to low cost
of ownership of the equipment
NationaVInternational
standards called up within
legislation
t
Professional bodies
concerned with EMC
Standards. (ENELEC, IEC
VDE,SAE,IEE,CISPR etc.j
Product manufacturerCompilation of all
stipulated EMC requirements
EMC requirements
for reliable product.
for the new product
(eg. immunity requirements
additional to those specified
~L----r----j.4--nE~lec;;rrtricairoilssdaff8ei\;ty;----'
by customer/legislation.)
requirements
Consider competitors' policy
on EMC
~-----'
Consider cost of
implementing EMC
r-
Generation of
....._---1 Consider manufacturer's
technical EMC capability
EMC requirement
hierarchy for product
being developed
Export marques EMC
requirements considered
. Consider marketing
advantages of lower
through-life cost of ownership
Marketing input: Sales
volume/Customer/Countryl
EMCspec.
Consider company quality
image is enhanced by
good EMC
System level
EMC specification
for new product
Figure 13.1
Generation of EMC requirement for product development (Example: manufacturer of desktop computer
products)
Figure 13.1 shows a typical flow chart for
generating product EMC requirements. There is
insufficient space available here to discuss individually each item in the chart, but the short titles
act as a reminder to consider that topic as part of
the checklist. Some insight into the central process
of assessing individual customer requirements and
developing a system level hierarchy of EMC test
standards which must be met, is given by Barrett
and Scherdin [8J, in the case of ind ustrial controIs
products produced by Texas Instruments. They
found that products had to meet up to 30 test
standards to satisfy all their customers' needs.
After considering the issues shown in Figure 13.1
they were able to narrow this down to a
minimum of 15 test standards. In the case of a PC
manufacturer who intends to sell world wide the
product may have to meet 5-10 standards to
cover the full range of EMI emission and
immunity, ESD and power line transient requirements.
13.4 Developing an approach to EMC
design
13.4. 1 Process flow chart
Once the system-level EMC requirement for a new
product has been determined the product manager
and her technical team must decide how to
approach the EMC design process as part of the
overall product development programme. There are
many ways to do this depending on the product, the
company, and the individual talents and expertise
available. One example, which again acts as a
checklist, is given in Figure 13.2. Two features of
this flow chart meri t further discussion.
13.4.2 EMC strategy
There are two fundamental approaches to ~eeting
the emission regulations for products. The first has
traditionally been favoured by the military for
ACHIEVING PRODUCT EMC: CHECKLISTS FOR PRODUCT DEVELOPMENT AND TESTING
System level
EMC requirement
Develop an approach
to system & subsystem
EMC design
Technical resources:
. tackle project in-house?
Use consultants?
Do both?
t
IN-HOUSE
Consider:
Staff expertise
Training in EMC
Capital equipment
Location of EMC
within company
structure
I
I
+
Mainstream product
design constraints
~
243
Figure 13.2 .Developing an
approach to EMC design
EMC STRATEGY:
Containment?
Source suppression?
Tackle immunity before
emissions?
Do the minimum?
CONSULTANTS
Balance of shortterm advantage to
long-term reliance.
Cost
Accountability
Selection of:
Technical design of
'EMC' sub syfems
(Technical plan)
their procurements and is based on the concept of
containment. 1--'hus the EMC subsystem designs
will be based around the techniques of screening,
filtering and shielding of cables with less attention
being paid to suppression of the interference
signal sources. Such an approach is viable for
military products which usually have stout metal
cases and require strong semiarmoured cables,
and where cost may not be the overriding consideration in product design.
EMC designers of commercial products, which
are usually lower cost and may have features such
as plastic cases and unshielded cables, have
tended to suppress EMI at source wherever
possible by careful signal shaping/band limiting,
the use of screened/filtered subsystems and low
radiation PCB designs. Staggs [9J suggests that
around 1984 the optimum balance for PC-type
products was to use a 50/50 strategy for
containment and source suppression. However
with the advent of very fast 32 bit chip sets
running at 25 MHz or more (resulting in high
peak switching currents) source su ppression
becomes more difficult and the balance shifts
more to a 60/40 containment/suppression ratio.
13.4.3 Immunity first?
For IT products, current enforceable EMC
regulations are limited to radiated and conducted
emissions and therefore meeting these regulations
will have a very high priority in the system EMC
requirement for a new IT product. It should be
remembered that the FCC in the USA has the
power to introduce immunity standards if the
voluntary system to ensure product EMI
immunity fails to work. In Europe there are a
Project EMC
control plan!
management plan
number of published draft standards which will
cover product immunity to EMI in future years.
The performance of the product in use can be
seriously reduced by EMI if it is susceptible, and
this will result in a poor reputation for reliability
for the product and the company. The field
service and warranty costs can be high if
equipments are continually in need of repair
owing to disruption or damage from EMI and
ESD/power transients. It has been estimated [9J
that for a machine population of 20,000 units
over five years the total gross savings in field
repair and warranty could be as high as $2.77 M,
with the cost of implementing EMC at $42 per
unit, this results in a net saving of almost $2 M.
For all these reasons it n1akes good sense for the
product development team to insist that new
products are designed with EMI immunity as a
high priority. For the example of a fast 32 bit PC
where the emphasis is on containment rather than
source suppression, this strategy becomes doubly
attractive as much of the shielding, filtering and
screening needed for immunity reduction will be
required anyway for emission suppression. Staggs
[9J comments that, 'by solving the immunity
problem first, and consequently lowering the
emission levels, the incremental cost of specific
emission solutions is relatively small'. For PC-type
equipments he estimates that 80% of emission
problems will be solved by meeting immunity
standards first.
13.4.4 Example of EMC design process
The considerations taken into account In
developing the overall approach to achieving
EMC for a new product (Figure 13.2) are
244
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
Approach to
and constraints
on mainstream
electronic design
Consideration of
bought-in items.
(Some may have
EMC features
built-in)
Sub system level
EMC specifications
eg. for case, keyboard,
interfaces, chipsets,
PSU etc.
.....- - - - t
I
_ _ _ ...I
System level EMC
strategy:
containment
source suppression
immunity/emissions
technical resources
EMC project control plan
- including the generation
of a technical
construction file
Detailed EMC design activity on each sub system
(including EMC development testing and
practical computer modelling)
EMC test plans for
- development
- conformance
- technical file
FOR MINOR PROBLEMS
MODIFY ONE OR MORE
SUBSYSTEMS
Subsystem integration
and pre-conformance
testing
Figure 13.3
,If fail, re-examine
1--_ _
--11.... design of sub systems
Example of EMG1 design process
contained within the larger design process. Figure
13.3 illustrates the issues that need to be
addressed to progress from the system-level EMC
requirement to a preproduction unit which is
ready for EMC certification.
Managers in small companies may shy away
from including mathematical modelling as part of
the design process. If staff have the skill to use
computer models and are able to interpret the
results so that competing design solutions can be
evaluated, and only the best option tested and
compared with the predictions, the use of
modelling can often be beneficial. If the decision
is made to use mathematical models the question
arises as to which models to use. They range from
those req uiring large mainframe machines down
to those based on simple assumptions (such as the
models described in Chapter 12) and which
req uire only a calculator or PC.
The question of the appropriate level of models
has been addressed by Atkinson [10]. He
considers that practical and useful EMI models
lie somewhere between the big-machine models
and the simple models used for scoping EMC
problems. He proposes the use of models based on
spreadsheet techniques that can run on a PC and
enable the engineers to describe and visualise the
EMI characteristics of the system being designed.
The successes (and the failures) of such models to
predict solutions to EMI design problems can be
used to support building a compu ter based expert
system which then becomes a valuable part of the
design process itself and which is applicable to the
design of the next generation of systems.
13.5 Technical construction file
13.5.1 Routes to compliance
options
During the development of an approach to EMC
design (Figure 13.2), and the subsequent desig!l
process (Figure 13.3) a decision will have been
made in most cases to opt for confirmation of a
successful EMC design by one of two methods: by
conformance testing, or by the submission to a
recognised assess men t body of a technical
construction file. A decision to test or submit a
technical file has implications for the EMC
programme cost and time to market. I t depends
on a number of factors related to the availability
of appropriate EMC standards, product type,
size, numbers made and installation features. If a
ACHIEVING PRODUCT EMC: CHECKLISTS FOR PRODUCT DEVELOPMENT AND TESTING
technical file is to be generated it will usually
contain some test data, but not at conformance
test level. The requirement for the generation of a
technical file which would be acceptable to meet
the needs of the EC EMC directive 89j336 is now
examined.
•
13.5.2 Circumstances requiring the
generation of a technical file
An early document containing guidance to manufacturers for the preparation of a technical
construction file which would meet the requirements of the Ee EMC directive has been
prepared by working party WP-3 of NAMAS
WG4 [4]. It lays out the circumstances where it
may be appropriate to use a technical construction file in aid of the EMC certification of
products. These are:
(i)
(ii)
(iii)
(iv)
(v)
For apparatus for which harmonised EC
EM C standards do not exist or are not
appropriate.
For apparatus for which standards do exist
but which are not applied in full. I t may be
possible for the manufacturer to claim that
the fund amen tal req uiremen ts of the
standard are met without performing any
or all of the required tests.
For
installations
where
testing
to
harmonised standards is not practicable due
to the physical properties of the installation.
For installations where testing of each installation is not practicable due to the existence
of large numbers of similar installations.
Combinations of the preceding circumstances.
13.5.3 Contents of a technical file
Each of the four basic circumstances listed results
in a slightly different requirement for the contents
of a suitable technical construction file. Take the
example of the second condition where the
standards are not applied in full. For this
situation the technical file shall contain the
following as a minimum.
•
•
A general overview. Statements should be
made that seek to demonstrate why tests for
certain phenomena were not felt to be
necessary. The key activity must be to
demonstrate what special. properties the
construction of the apparatus has which
render unnecessary the required EM C tests in
the appropriate standard.
Identification of apparatus. Typical contents
should include
Brand name
Model number
•
245
Name and address of manufacturerj
importer
Purpose of equipment
Performance specification (EMC-relevant)
External photographs of the equipment
Technical description of the equipmen t.
Typical contents should include, but not
necessarily be restricted to,
Full technical description including block
diagram showing the interrelation of the
functional areas
Set of technical drawings
Components list, with special regard to
microprocessors, RAM,
ROM,
logic
families, oscillators, power supplies, motors
and relays
Signal
data
including
frequencies,
risetimes, switching curren ts, grounding
schemes
Description of physical characteristics of
the equipment, SIze, weight, power
consumption
Listing of available purchase options of the
equipment
List of other equipment likely to be
connected to the device being assessed
Description of any design measures taken
specifically to control EMI and enhance
EMC performance of the product
A copy of any assembly or installation
manuals supplied to the customer which
may affect its EMC performance.
Technical rationale. This must explain in
detail why the harmonised ECEMC
standards have not been applied in full. It
should be supported where possible by
information derived from theoretical and
practical studies. Details of all tests performed
should be included. Explanation of the
quality control procedures that apply to the
product must be given to show that future
samples of the equipment will also comply
with the directive. The detailed contents of
the technical rationale should include, bu t not
be limited to, the following:
The logical process used to determine that
certain tests need not be performed. For
each type of test described in the
standards and which has not been
performed, a description and explanation
of the results of any relevant development
tests. Support for the decision not to
perform certain tests with any theoretical
studies which show that the apparatus
must inherently comply. The description
of any EMC design measures relevant to
the phenomenon being assessed in tests
246
A HANDBOOK FOR EMC TESTING AND MEASUREMENrr
which have not been performed. A detailed
analysis of the method of operation,
relevance and expected effectiveness of
any EMC protection measures incorporated into the equipment.
A list of all formal tests and reports which
have been carried ou t.
An account of how the EMC performance
of production samples will be verified, and
how the sampling levels will be chosen.
An account of variant and build standard
control in production and an explanation
of the procedures used to assess whether a
design change requires the apparatus to
be retested/requalified.
13.5.4 Report from a competent body
1'he technical construction file must be submitted
to an organisation which is deemed by the
regulatory authorities to be competent to judge
the performance of the apparatus in relation to
the harmonised EMC standards. Competent
bodies are likely to include NAMAS approved
EMC test houses and some EMC consultancies.
The report from the competent body produced as
a result of assessing the technical file should
include
Reference to the exact build standard of the
apparatus assessed and a cross reference to the
technical file.
Statement on the work done to verify the
contents of the technical construction file.
Comments on the procedures used by the
manufacturer to ensure compliance with the
EC directive for each phenomenon described
in the relevant standard for which formal tests
have not been performed.
Comments on any tests which were carried
out, and an analysis of test methods employed.
Comments on q uali ty assurance procedures
which the manufacturer intends to apply to
the product.
T'he report from the con1petent body can be used
by the manufacturer of the equipment to support
his statement of compliance with the EC directive
on EMC.
13.5.5 1'esting or technical file?
I t would be incorrect to suppose that the
generation of a technical file and its submission to
a competent body for scrutiny is necessarily an
easy way of obtaining EMC clearance to Inarket
a product under EC 89/336. The testing option
may prove less costly in some cases and if suitable
test facilities have been booked in good time there
should be little extra delay in bringing the
prod uct to market. Experience will be gained
during the 1990s as to when the technical file
rou te as opposed to conformance testing is most
appropriate for product approval. For large, oneoff type eq ui pmen ts it maybe impossible to carry
out approved tests and the technical file is then
the only route to EMC clearance. In the years to
come all Inanufacturers and EMC practitioners
will watch with interest the developments
surrounding this question.
13.6 Self certification
13.6. 1 Need for an in-house facility
The option to self certify products under the EC
regulation can be very attractive to some manufacturers. If they originate a continuing series of new
products or new variants of existing products,
then it may be cost effective to develop an inhouse capability to carry out the necessary EMC
conformance tests.
The particular list of EM C tests required by
standards will be product specific, and a manufacturer's in-house facility need not cover such a wide
range of tests as would an all-embracing third
party EMC test house. The exact list of EMC
tests with which the in-house facility must cope
will
have
been
determined
during
the
development of the product design. rrhe basic
types to be considered are
emission tests -- conducted and radiated
immunity tests
conducted and radiated
screened enclosure testing
open-area test site
ESD and transient testing.
The technical details of all these types of tests have
been covered in preceding chapters.
An additional consideration for defining the
requirement of an in-house test facility is the size of
the equipment to be tested. Generally, this is the
key cost driver, the greater the EUT size the
greater the cost of the test facility. The break point
comes for EUTs about 1 m cube. If they are larger
than this the facility will be very expensive if
radiated immunity/susceptibility testing is to be
carried out using semi-anechoic screened chambers.
Anyone considering the technical definition and
financial investment required to develop an EMC
facility should consult as widely as possible
existing facility operators dealing with their
product types to avoid making potentially costly
mistakes. Time permitting, the safest route to
constructing the most suitable and cost-effective
in-house facility is to build it up in a series of
levels of capability.
ACHIEVING PRODUCT EMC: CHECKLISTS FOR PRODUCT DEVELOPMENT AND TESTING
13.6.2 Gradual development
The risks associated with these issues can be
reduced by a gradual approach to developing an
in-house EMC test capability which has three
basic levels:
There are four components which need to be considered when developing an in-house EMC facility:
(i)
(ii)
(iii)
(iv)
Defining and obtaining the correct accommodation, facilities and test equipment to
perform the range of tests specified in the
chosen EMC standards.
Having sufficient well motivated and
qualified test personnel available.
Putting in place sound workable operating
and q uali ty control proced ures to guide the
technical staff using the equipment to carry
out the tests.
Ensuring the right amount of work for the
facili ty - too li ttle, and morale will fall,
along with any continued investment in
staff training and new equipment; too
much, and the facility will be overloaded,
resulting in potential errors in test work and
pressure to compromise quality standards.
In such circumstances the staff would have
no time for training and attending
conferences, etc. which would result in little
or no development of their skills. The latest
information relating to test methods and
equipment would not find its way into the
facili ty and benefit the conformance testing
which helps get the products to market.
Level 1:
Bench testing to serve product development
Developing dedicated facilities i.e. an
open-area test site or a suitable
screened enclosure plus the associated
test equipment
Upgrading these facilities to conformance test standards
Obtaining accreditation for
the
facility.
Level2a:
Level2b:
Level 3:
This process is shown In Figure 13.4. Self
certification of products is clearly possible at
level 3 but may also be substantially risk-free
at level 2b if care is taken to operate in the
professional manner req uired by N AMAS (at
level 3).
rrhe information contained in this and other
books on EMC can be helpful in determining the
tests/standards which must be covered (for
various product types) and the technical
knowledge required to specify and use EMC test
equipment in approved ways to measure the
required parameters of current, field strength and
immunity level, etc.
Bench-test capability for development testing
includes: conducted emissions
ESO & transients
near-field radiated
emission probes
Up-grade 'OATS to
conformance test
standard.
(Gain experience)
Obtain accreditation:
can now self-eertify
products with
confidence.
(Sell spare capacity)
~
H
Screened room test facility
for radiated emission and
susceptibility development
testing
Introduce strict lab.
procedures, calibration and quality
control to 'NAMAS'
standard
~
------------------ LEVEL 20
Up-grade to
conformance
test standard
(Gain experience)
-------- LEVEL 2b
Obtain accreditation
Seek NAMAS II--_~ (up-grade capability
accreditation I
with higher susceptibility
field strengths and
--------- LEVEL 3
accommodate larger
test objects)
(Sell spare capacity)
+
Figure 13.4
-------------------------LEVEL 1
THIS ROUTE FOR
MILITARY AND SOME COMMERCIAL
PRODUCT TESTING
THIS ROUTE FOR
EMISSION TESTING OF
COMMERCIAL PRODUCTS
Open-area test site
for radiated emission
development testing
247
Steps to consider when setting up in-house.EMC test facility
+
248
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
13.6.3 Es tilllates of facility cost
When all the consultants have gone, the
purchaser is left with an impressive facility
but perhaps without the necessary trained
staff, facility operating procedures, or
backup support, unless they have been
included as specific req uirements in the
turnkey package, at an extra cost.
An estimate of the typical equipment cost to set up
an EMC test facility with various capability levels
in line with those previously described
1 to 3), is given in Figure 13.5. l'hese
estimates do not include the additional costs of
land or buildings which facilities would occupy.
No cost has been included for the recruitment and
training of
EM C test personnel.
l'he
of facilities is often a critical
within companies wishing to develop an
EMC test capability. There is usually a shortage
of
qualified and experienced staff in the
UK and often only premiurn conditions will
attract the best people. Developing the necessary
expertise completely on the basis of existing
company staff is also expensive due to the cost of
training, which takes from 1 to 3 years.
l'he conclusion is clear: anticipate the EMC
product development needs of the company, plan
for a phased build-up of facili ties and expertise to
meet the need, recruit and/or train the
appropriate in-house staff to run the facility.
13.7 Conclusion
Electromagnetic compatibility is a fascinating and
rapidly developing field of electrical engineering.
It poses important, interesting and wide ranging
multidisciplinary
challenges
to
equipn1ent
designers. I t affords many technical challenges
which must be met by engineers, to Inake
consisten t and meaningful measurements of
complex EMI quantities. The managernent and
quality aspects of EMC work are equally
in1 portan t if the technical effort expended is to be
realised in terms of added value to the products
being developed.
In its widest role, EMC is part of the growing
realisation that the benefits of industrialisation can
only be enjoyed to the full if one takes care to
minimise the unwanted impact of the technology
employed. For example, without EMC controls,
what would be the net benefit of the advent of
powerful desktop business computers if the electrical
emissions _from them disturb and compromise each
other or the communications systems which carry
the data generated to other uses?
13.6.4 Turnkey facilities
If time is pressing and a complete facility must be put
in-house in a short time, it is possible to
contract a consultant or possibly an EMC equipment manufacturer to deliver an adequate turnkey
£0.5 M-£l M) within about 6-9
months. Developing the requirement specification
for such a programme would be the main activity
which the purchasing company would have to
undertake. I t is
to use a second set of consultants to do this and to monitor the performance
of the ITlain contractor supplying the turnkey facility.
rrhere are two main weaknesses inherent in this
It is
cover
to be costly: the additional cost to
factors could be substantial
(10 (Yo ---20 % of the turnkey price).
risk
£10k
£100k
£500k
I
£1 m
!SIMPLE SPECTRLM ANALYSER & !URRENT PROBE(& NEAR-FIELD
1r
-
BENCH
~OP C.E. & E.S.D. ~ SOME TRANSIENT TESTING
I
I
I
£10m
£100m
P~OBES FOR BENC~ TOP TESTING
I
I
I
*SMALL SCREENED ROOM C.E. & E.S.D. -& TRANSIENTS & R>E> & R.S. (1 Vim to 1GHz)
I
I
I EMI METER)
*O.A.T.S.,
R.E. UP ITO 1GHz (SPE. ANALYSER
OR CHEAP
I
I
I
lICOMPREHENSIVE CHAMBER-BASED FACILITY CAPABLE OF
R.S. UP TO 10V/m & R.E. UP TO 1S-GHz & C.E. & ESD & TRANSIENTS
I
I
I
*MULTI-CAPABILITY COMMERCIAL TYPE EMC TEST HOUSE FACILITY
I
I
I
*HIGH CAPABILITY MULTI-PURPOSE FACILITY
FOR COMMERCIAL & MILITARY TESTING OF
SYSTEMS UP TO 4 X 3 X 2m
I
I
* A NATJONAL LEVEL TEST FACILITY FOR
A MAJOR MILITARY OR CIVIL PRODUCT
...::1---.....
BENCH TOP
LEVEL 1
13.5
...
DEDICATED FACILITIES CONFORMANCE TEST FACILITIES
til
LEVEL 2
...
LEVEL 3
.. ....
cost against capabilify (1991
£
Sterling)
I
I
MAJOR NATIONAL
FACILITIES---.........
ACHIEVING PRODUCT EMC: CHECKLISTS FOR PRODUCT DEVELOPMENT AND TESTING
EMC will be a major area of expanding interest
and influence in the decade of the 1990s as
legislation drives the commercial world to strict
compliance with national and interna tional
standards.
Electromagnetic compatibility is then a branch
of electrical engineering which has a clear
commercial and social impact, and its practitioners will con tri bu te in a small way to the
future quality of life in an environment which
increasingly interacts with technology.
13.8 References
'The
Single
Market
Electromagnetic
Cornpatibility'. HMSO, 2/90. Dd 8240964 INDY
Jl077NE 40M, Feb. 1990
2 'Electrical interference: a consultative document,
The implementation in the UK of Directive 89/336/
EEC on electromagnetic compatibility'. Available
from L.B. Green, Radiocommunications Division,
DTI, Rm 106, Waterloo Bridge House, Waterloo
Road, London SE1 8UA
3 'The Single Market: EMC Update'. DTI
Radiocommunications Division, Waterloo Bridge
4
5
6
7
8
9
10
11
249
House, Waterloo Road, London SEl 8UA, June
1990 and March 1991
'Guidance document for the preparation of a
technical construction file as required by the EC
directive 89/336, A draft for discussion'. From
A. Bond, MT Division 4e, DTI, 151 Buckingham
Palace Road, London SW1
'Points of contact'. NPL0004/8K/NJ/6/90, NPL,
Teddington, Middlesex, TW11 OLW, 1990/91
'Concise directory - M3'. NAMAS Executive, NPL,
Teddington, Middlesex, TWll OLW, Aug. 1990
Special edition on EMC, New Electronics, October
1990
BARRETT, J.P. and SCHERDIN, S.: 'The
development of EMC laboratory standards and
procedures'. Proceedings of IEEE symposium on
EAfC) 1990, pp. 329-332
STAGGS, D.M.: 'Corporate EMC programmes'.
Proceedings of IEEE symposium on EMC) 1989,
pp. 320-325
ATKINSON, K.: 'Graphical EMI modelling
spreadsheet'. Proceedings of IEEE symposium on
EAfC) 1990, pp. 175-179
'Help is at hand - useful contacts for advice and
technical information'. DTI EMC awareness
campaign, . Findlay Publications, Franks Hall,
Horton Kirby, Kent DA4 9LL, May 1993
Appendix 1.1
Signal bandwidth definitions
NARROWBAND SIGNAL (CW)
1 Narrowband/broadband signals
3 dB BANDWIDTH
Signals measured during radiated and conducted
emission tests are often extremely complex,
consisting of a mixture of individual signals from
many separate sources within the equipment.
Some of these may emanate from stable oscillators
for example, producing a sinusoidal waveform at
a single frequency. The frequency extent or
bandwidth of this signal is small, perhaps less
than 1 Hz, and it is clearly narrowband.
Other circuits which generate fast switching
waveforms such as switched mode power supplies
or digital processing circuits produce signals
which contain many frequency components which
may be spread across tens or hundreds of
megahertz. These. signals have a wide bandwidth
with the highest frequency being determined by
the switching-edge risetime/falltime, and the
spacing of frequency components in the spectrum
by the switching repetition frequency. Such a
signal is referred to as broad band.
«
o
en
W
r--
~
I
W,
...Ji
Narrowband signal
frequency f 1
I
OdB--
Bandwidth 11kHz
Cl
::::>
Bandwidth 210kHz
:.J
a.
/Bandwidth 3 30 kHz
.....
~
«
FREQUENCY
BROADBAND IMPULSE SIGNAL
6 dB IMPULSE BANDWIDTH
I
W
..J
«o
en
I
r-
I
Wide bandwidth 10MHz
Wide bandwidth 1MHz
w
Wide bandwidth 100 kHz
Cl
::::>
Wideband impulse signal
spectrum with many
frequency components
I-
::J
0-
~
«
2 Measuretnent of narrowband and
broadband signals
I
FREQUENCY
1
t
Measuring the amplitude of a narrowband signal
with a tuned radio receiver or EMI meter is
simple, as once the receiver is tuned to the signal
frequency at say 11 MHz, the measured signal
strength is independent of the bandwidth used to
measure it. This is because all the power in the
signal is always contained within the 3 dB
passband of even the narrowest IF (intermediate
frequency) and post-detector filters as shown in
Figure Al.la.
This is not the case with broad band noise or
impulsive signals where the power in the signal is
distributed over a range of frequencies which is
much greater than the receiver bandwidth which
is used to measure it. Figure Al.lb shows a
typical impulse spectrum from a digital switching
waveform which has frequencies out to perhaps
100 MHz. It is represented as a series of frequency
components spaced at 1/ T (where T is the signal
PRF) and a first null at lit (where t is the
risetime /fall time). The signal power intercepted
under the IF filter bandwidth increases as the
bandwidth increases. Thus the measured power
and indicated signal voltage referred to the
Figure A 1.1
Narrowband/ broadband signals
receiver input, increases with the bandwidth used.
The shape factor of the IF filters becomes
important as it affects the intercepted signal
power and therefore the indicated signal voltage.
'To derive a signal level that is universal, irrespective of the bandwidth used, the measurement
must be expressed in power or voltage per unit
bandwidth. This is called the signal spectral
density and for EMC measurements it is usually
expressed in /lV/kHz or /lV/MHz. When the
calibration of the sensor connected to the receiver
is taken into account the measurements of
physical quantities are expressed as dBIlV /m/kHz
or dB/lV /m/MHz for radiated emission field
strengths and dB/lA/kHz or dBIlA/MHz for
conducted emissions.
For pure broadband thermal n~ise where the
signal power at each frequency is phase
incoheren t, the measured signal vol tage increases
as the square root of bandwidth used. For
coherent impulsive noise (where there is a defined
250
SIGNAL BANDWIDTH DEFINITIONS
phase relationship between adjacent frequency
components)
the
measured signal voltage
increases proportional to bandwid th [1] . Some
broadband signals will not fall neatly into either
category and for these the change in measured
signal voltage wi th a change in receiver
bandwidth will lie between that for incoherent
and coherent signals.
The
precise
defini tion
and
consisten t
measurement of broadband signals is a major
issue in EMC testing. Some EMC standards
overcome the difficulty by specifying the precise
receiver IF bandwidths which must be used for
measurement at different frequencies. This means
that all measurements will be made in the same
way without the test engineer making a judgment
251
as to whether the signal is narrowband or
broadband.
The discussion in the EMC community about
narrowband/broadband measurement seems to be
moving to a conclusion where most commercial
and
military standards will adopt fixed
bandwidths. Those EMC test engineers who are
req uired
to
measure
broadband
signals
normalised to 1 kHz or 1 MHz bandwidth should
exerCIse care with this aspect of measurement
technique.
DUFF, vV.G.: 'Fundamentals of electromagnetic
compatibility'. Interference Control Technologies
Inc., Gainesville, Virginia, USA, sections 2.6, 2.7,
pp. 2.38-2.44
Appendix 1.2
UK EMC legislation
(up to 1 January 1996)
Statutory instrument
Title
1952 2023
The Wireless Telegraphy
(Con trol of interference
from ignition apparatus)
Regulations 1952
The Wireless Telegraphy
(Control of interference
from electro medical
apparatus)
Regulations 1963
The Wireless Telegraphy
(Con trol of interference
from radio frequency
hea ting a pparatus )
Regulations 1971
The Wireless Telegraphy
(Control of interference
from household appliances,
portable tools, etc.)
Regulations 1978
The Wireless Telegraphy
(Control of interference
from f1 uorescen t lighting
apparatus)
Regulations 1978
The Wireless Telegraphy
(Control of interference
from CB radio apparatus)
Regulations 1982
1963 1895
1971 1675
1978 1267
as amended
1978 1268
1982 635
as alnended
objective, but not designed by the manufacturer (s) for supply as a single technical unit.
Spare parts, subject to regulation 14(2) of the EC
EMC Regulations whereby nothing shall be taken
to affect the application of the regulations to
relevant apparatus into which a spare part has been
incorporated. 'Spare part' means a component or
combination of components intended for use in
replacing parts of electrical or electronic apparatus.
Supply of apparatus to authorised representative
responsible for complying with the regulations.
Second-hand apparatus is excluded, with the
exception of such apparatus which has, since it was
last used, been subjected to further manufacture;
and second-hand apparatus which is either
supplied or taken into service in the community for
the first time having previously been supplied or
used in a country or territory outside the
community. Second-hand apparatus means that
which has previously been used by an end user.
Electromagnetically
benign
apparatus
is
excluded where the inherent qualities of the
apparatus are such that neither is it liable to
cause, nor is its performance liable to be degraded
by, electromagnetic disturbances.
2 Specific exclusions
The EC EMC regulations do not apply to:
Apparatus for use in a sealed electromagnetic
environment so long as it is accompanied by instructions stating that the apparatus is suitable for use
only in a sealed electromagnetic environment.
Radio amateur apparatus which is not available
commercially is excluded.
Military equipment defined as apparatus which
is designed for use as arms, munitions and war
material within the meaning of Article 223.1 (b) of
the Treaty establishing the EEC (notwithstanding
that it may be capable of other applications), but
does not include apparatus which was designed
for both military and non-military uses.
Exclusions from. EC harm.onised
EMC regulations
rrhis information is taken from the DTI
publication 'Product standards electromagnetic
compatibility (UK Regulations April 1993)'.
1 General exclusions
The EC EMC regulations do not apply to:
Apparatus for export to a country outside the EEC
where the supplier believes with reasonable cause
that it will not be used in the UK or another
member state.
Some installations are excluded where two or
more combined items of equipment are put
together at a given place to fulfil a specific
3 Apparatus wholly covered by other
directives
The EC EMC regulations do not apply to:
Active implantable medical devices within the
252
UK EMC LEGISLATION
meaning of Article 1.2 (c) of the Council Direc tive
90/385/EEC.
Medical devices covered by. the EC directive in
preparation
(1993)
and
comprising
any
instrument, apparatus, appliance, material or
other article, including software for the purpose of
(a)
(b)
(c)
diagnosis, prevention, 'monitoring, treatment
or alleviation of disease, injury or handicap
investigation, replacement or modification of
the anatomy or of a physiological process
control of conception.
4 Apparatus partly covered by other
directives
The EMC regulations do not apply to
Electrical energy meters as regards the immunity
253
thereof (regulated by Council Directive 76/89/EEC).
Spark ignition engines of vehicles in so far as the
electromagnetic disturbance generated thereby is
liable to cause radio interference (such interference is regulated by Council Directive 72/245/
EEC).
Spark ignition engines of tractors in so far as the
electromagnetic disturbance generated thereby is
liable to cause radio interference (such interference is regulated by Council Directive 75/322/
EEC and as amended by Article 1 of 82/890/
EEC).
Nonautomatic weighing machines as regards the
immunity thereof (regulated by Council Directive
90/384/EEC).
rrelecommunications terminal equipment (TTE)
to the extent that EMC requirements are
determined by Council Directive 91/263/EEC.
Appendix 1.3
European EMC standards
Listed in Table Al.3.1 are commonly used
European EMC standards, their applicability and
equivalent national standards. In some cases a
near equivalent USA standard is also identified.
Table Al.3.1 EMC standards (emissions)
Equipment
Euro standard
Generic emission
ISM
EN50081
EN55011
Radio and TV receivers
EN55013
Household appliances
EN55014
Lamps and lighting
IT equipment
EN55015
EN55022
Electrical supply networks
Vehicle igni tion systems
Motor cycles and vehicles with 3 or
more wheels
Vehicle brakes
Metrology (weights and measures)
EN60555
75j245jEC
UN ECE Reg.10
Equivalents
BS4809, VDE0871, CISPR11
(FCC pt18)
BS905 pt1, VDE0872, CISPR13
(FCC ptl5)
BS800, VDE0875, CISPR14
(FCC pt15)
'BS5394, VDE0875, CISPR15
BS6527, VDE0871, CISPR22
(FCC ptl5)
BS5406, IEC555
BS833, CISPR12
71j320jEEC, UN ECE Reg.13
NW0320
EMC standards (immunity)
Generic immunity standard
Broadcast receivers
Industrial process control
EN50082
EN55020
HD481
IT equipment
EN55101
BS905 pt2, CISPR20
BS666 7, IEC80 1-1, IEC80 1-2
(BS6667 (1985)), IEC80 1-3
IEC801-5
254
EUROPEAN EMC STANDARDS
255
Table A1.3.2 Existing EC harmonised standards: emission standards (up to 1993)
Compiled from References 16 and 17 of Chapter 2
CENELEC
reference
Draft for public
comment
British Standard
Mains signalling on low voltage electrical
ins tallations.
EN50065-1 *
EN50081--1 *
90/26273 DC
EN55011*
BSEN550 11: 1991
EN55013*
BS905: 1991: ptl
EN55014*
Equipment covered
90/20911DC
[proposed rev]
BS800: 1988
EN55015*
BS5394: 1988
EN55022*
BS6527: 1988
Any equipment in the domestic, commercial
and light industrial electromagnetic
environment (class 1 environme'nts) - generic
emission standard.
Limits and methods of measurement of radio
interference characteristics of ISM RF
equipment (excluding surgical diathermy
apparatus). Based on CISPRII
Limits and methods of measurement of radio
interference characteristics of sound and
television receivers. Based on CISPR 13
Limits and methods of measurement of radio
interference characteristics of household
electrical appliances, portable tools and similar
electrical apparatus. Based 'on CISPR 14
Limits and methods of measurement of radio
interference characteristics of fluorescent lamps
and luminaires. Based on CISPR15
Limits and methods of measurement of radio
interference characteristics of information
technology equipment. Based on CISPR22
EN60555-2*
88/27854DC
BS5406: 1988: pt2
EN60555-3*
90/28296DC
BS5406: 1988
Disturbances in supply systems caused by
household and similar equipment (harmonics).
Disturbances in supply systems caused by
household and similar equipment (voltage
fluctuations) .
BS4727: ptl: Gp9
EMC definitions
Standards not yet adopted
IEC50 chap161
* Denotes standards which have been referenced by the Official Journal of the European Communities and are therefore
notified for use in self certification.
256
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
Table A1.3.3 Existing *t and possible future EC harmonised standards: immunity standards
Compiled from References 16 and 17 of Chapter 2
CENELEC
reference
Draft for public
comment
EN50082-1 *
90/26272DC
Any in the domestic, commercial and light
industrial electromagnetic environments (Class 1
environment). Generic immunity standards.
prEN50082-2
91j21828DC
Any in the industrial electromagnetic
environment.
EN55020*
91 j25187DC
[proposed rev]
89j34172DC
prEN55101-2
British Standard
BS905: 1991: pt2
Equipment covered
Sound and TV broadcast receivers and
associated equipment.
Information technology equipment.
Electrostatic discharge.
prEN55101-3
89j34171DC
ITE
Radiated RF disturbances.
prEN55101-4
90/30270DC
ITE
Conducted RF disturbances.
HD481
(IEC801)
HD481.1SI
EMC for industrial process measurement and
control equipment.
BS6667: 1985: pt1
General introduction.
HD481.2SI
BS6667: 1985: pt2
Method of evaluating susceptibility to
electros ta tic discharge.
HD481.3SI
BS6667: 1985: pt3
Method of evaluating susceptibility to radiated
electromagnetic energy.
IEC801
IEC801-3
(Draft Rev)
IEC801-4:
1988
IEC801-5
(Draft)
IEC801-6
(Draft)
Electromagnetic compatibility for industrial
process measurement and control equipment.
Immunity to radiated RF EM fields.
90j29283DC
BS6667: pt4
Electrical fast transient/burst requirements.
90j21076DC
Surge immunity requirements.
90/27512DC
Immunity to conducted RF disturbances above
9KHz
* Denotes standards which have been referenced by the Official Journal of the European Communities and are therefore
notified for use in self certification.
tup to 1993
EUROPEAN EMC STANDARDS
257
Table A1.3.4 Proposed product-specific EMC standards (introduction into EEC by 1996)
Industrial
1.
2.
3.
4.
5.
6.
7.
7a.
8.
9.
10.
CENELEC ref.
Industrial measurement and control equipment
Machine tools (electronic control of manufacturing machinery robots)
Power electronics (convertors, rectifiers etc)
Industrial electroheat equipment
Electrical welding
Industrial transport equipment (cranes)
Power capacitors
Related filters
LV switchgear and control gear
Rotating machinery
FusesLV
Residential) commercial and L V professional
1. Audio, video, audiovisual equipm.ent for domestic entertainment
1a. Broadcast satellite receivers
2. Audio, video, audiovisual lighting control equipment for professional use
3. Domestic appliances and similar household appliances (including toys)
4. Lighting
5. Alarm systems (without mains connection)
6. Mains signalling in low-voltage
7. Building automation
8. Small power electronics (power supplies)
9. Lifts
10. LV circuit breakers and similar equipment
11. Residual current devices
12. Electronic switches
Information technology equipment
ITE (including telecommunication terminal equipment)
ISDN
prEN55024
ENV55102-2
Traffic) transportation
1. Electric traction equipment
2. Motorway communication equipment and traffic control equipment
3. Electrical installation of ships
4. Navigational instrumentation
Utilities
1. HV switchgear and control gear (secondary systems)
2. Protection equipment
3. Telecontrol, teleprotection and associated telecommunication for utilities
4. Measuring, metering and load control apparatus (electronic)
5. HV fuses
Special
1. Medical equipment
2. Electrical and electronic test and measuring instruments (including scientific
instruments)
3. CATV cable distribution equipment
prEN50082-2
258
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
Table Al.3.5 CISPR publications
CISPRI
CISPR2
CISPR3
CISPR4
CISPR5
CISPRI-6
CISPR7
CISPR8
CISPR9
CISPRI0
CISPRII
CISPR12
CISPR13
CISPR14
CISPR15
CISPR16
CISPR17
CISPR18
CISPR19
CISPR20
CISPR21
CISPR22
CISPR23
RFI measuring set 0.15-30 MHz
RFI measuring set 25-300 MHz
RFI measuring set 10-150 kHz
RFI measuring set 300 MHz-l GHz
Peak, quasipeak and.average detectors
inclusive have been superceded by CISPR 16
Recommendations of CISPR
Reports and study questions
CISPR and national limits
Organisation, rules and procedures of CISPR (1981 and 1983)
ISM limits and measurements (1975, 1976)
Ignition limits and measurements (1978, 1985)
Sound and TV receivers limits and measurements (1975, 1983)
Household equipment limits and measurements (1985)
Fluorescent lamps and luminaires limits and measurements (1985)
RFI measuring sets specification and measurements (1977, 1980, 1983)
Filters and suppressors measurement (1981)
RFI of power lines and HV equipment part 1: description (1982)
Microwave ovens measurements above 1 GHz (1983)
Immunity of sound and TV receivers (1985)
Interference to mobile radiocommunications (1985)
II' equipment limits and measurement (1985)
Derivation of limits for ISM
Appendi)( 1.4
Gerntan decrees and standards
Table
~41.4.1
German decrees relating to Ell-lC
Decree
.A.pplicability
\lfg 523/1969
\lfg 1046/1984
Individual permit for HF equipment - Class A Decree
ISJ\tI and similar equipment (EDP, etc) - Class B general permit decree (includes self
certification ) [specifies VD E08 71 ]
General permit for household appliances [specifies VDE0875]
EC directives implementation and harmonisation of legislation [specifies 82/499/EEC and
82/500/EEC]
\lfg 1045/1984
\ffg 1044/1984
Examples of Germ,an VDE standards
VDE Ref.
Relating to
'iDE0565
Specification for RFI suppression devices
Part 1 Capacitors
Part 2 Chokes
Part 3 Filters (up to 16 A)
Part 4 Ceramic capaci tors
Limits of RFI from RF apparatus and installations
Part 1 ISNI
Part 2 EDPjIT
Interference suppression for radio and T\l receivers
RFI from electrical utility plants and H\l systems
Recommendation for RFI suppression
RFI from appliances (frequencies below 10 kHz)
Part 1 Household appliances
Part 2 Fluorescent lighting
Part 3 i\ppliances with motors
Interference measuring apparatus
Part 1 vVeighted indication
Part 2 Disturbance analyser
Part 3 Current probes
RFI NIeasurement procedures
Part 1 Interference voltage
Part 2 Interference field strength
Part 3 Interference on power leads
RFI suppression for motor vehicles and engines
VDE0871
VDE0872
VDE0873
VDE0874
\lDE0875
\lDE0876
VDE0877
\rDE0879
259
260
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
Table Al.4.2 Sun'lmary oj important test differences between USA (FCC) and Europe/ Gern'lany (VD E)
FCC
VDE
Class A
For commercial/office products.
Manufacturer does RFI test for self
verification and labels product
VDE RFI test and FTZ certification is
mandatory by law, primarily for systems
or low volume products. FTZ number
must be on product and user registers
device location.
Class B
For residential products only. Requires
FCC authorisation and FCC identifier
number on device
Can test at VDE or self certify. Used for
high volume and stand-alone products.
German RFI declaration and ZZF
registration required for self certification.
A 2 dB margin is required when one unit
is tested.
Class C
Class A equipment can be tested at
installation site for self verification.
The FCC does not perform this test
Test is conducted by local postal
authority at place of installation. Class C
is for large 'one-of-a-kind' systems
installed in an industrial zone.
Radiated test
distances
3 m for Class Band 30 m for Class A,
preferred. Distances less than 30 m
allowed if data are correlatable.
10m for Class B, 30 m for Class A
(10 m, 470-1000 MHz).
Cond ucted test
450 kHz-30 MHz, Class A and B
10 kHz-30 MHz, Class B. 150 kHz30 MHz, Class A. For Class B tests, when
a reading is wi thin 5 dB of the B limit,
then rerun test with floating ground.
Magnetic field
test
N/A
Performed per VDE0871 at 3 m from
10 kHz to 30 MHz. If EU'I' fails at 3 m
then retest at 30 m for Class B.
Radiated test antennas
An tenna height is varied from 1 to 4 m
for measurement distances up to and
including 10m. For distances of 30 m the
antenna is varied from 2 to 6 m
An tenna height is fixed at 3 m for up to
470 MHz and varied from
470-1000 MHz for Class A (30 m
distance). Antenna height is varied from
1 to 4 m for Class B (10m distance).
Radiated test cables
Interface cables are configured to
discover maximum emission
Interface cables are positioned at 1.5 m
out from EUT and parallel with ground
(see VDE0877).
RFI test
equipment
EMI receivers are preferred but spectrum
analysers are allowed. Spectrum
analysers are widely used in the US
EMI receivers with CISPR are highly
preferred. Spectrum analysers with QP
and preselection are sometimes
permitted. Spectrum analysers are rarely
used in Germany
Appendix 1.5
US EMC regulations and standards
Table Al.5.l FCC EM G~ regulations and information
Part 15
Part 15j
Part 18
Part 68
OST62
OST55
MP-4 Guly 87)
Standards for unlicensed or restricted radiation devices
Covers the limits for computing devices
Standards for industrial, scientific and medical equipment
Specification for equipment connected to telephone network
Understanding FCC EDP regulations
Open-field sites for FCC testing
FCC measurement procedures for EDP
Table Al.5.2 Examples of other US EMC standards
SAE J-551 C [20]:
SAE J -1113
SAEJ-1338
SAEJ-1407
SAEJ-1507
(1984).}
(1981)
(1982)
(1986)
Vehicle ignition interference. This places limits of -2 dB flV/in/kHz (30-88 MHz)
and 8 dB fl V /m/kHz (88-400 MHz) at 10m from the vehicle.
Concerned with radiated susceptibility testing of whole vehicles (not aircraft),
but could be applied to testing any large system
SAE ARP-937 [21]:
Jet engine EMI
SAE AIR-1147 [22]:
Precipitation static radio interference from jet engine charging
RTCA/DO-160B/C:
Environmental conditions and test procedures for airborne equipment
ANSI C63.2 [23J:
Specification for EMI and field strength instrumentation
Details of other US commercial specifications can be found in Appendix 1.9 in the compendium of EMC
standards.
[References relate to Chapter 2]
261
Appendix 1.6
Gerntan, North Anterican and Japanese
EMC standards
Table Al.6.1 Comparison oj VDE) FCC and VCC] test procedures
VDE
Horizontal antenna
distance (m)
Class A
FCC
VCCI
10 or 30
100 (H-field)
10
3 or 30 (H-field)
3, 10 or 30
3, 10 or 30
3, 10 or 30
3 or 10
Class A
1-4*
2-6
1--4
Class B
1-4*
1-4
1-4
Class B
Vertical antenna
height (m)
Floor-moun ted
equipment is placed on
nonconductive surface
at 0.15m max height
during test
Floor-mounted
equipment is placed on
floor
Floor-mounted
equipment is placed as
close as possible to metal
plane
Table-top equipment is
in normal operating
posi tion on a
noncond uctive test
stand at 0.8 m height
T a ble-rnoun ted
equipment is positioned
40 cm from ground that
LISN is referenced to
and at least 80 cm from
nearest other ground
Portable equipment is
placed on a non-metal
stand 0.8 m above metal
plane
Cable
For table-top
equipment, cables are
laid horizontally for
1.5 ill at table height,
then allowed to drop
vertically to floor. For
floor-level equipment,
cables are laid
horizontally for 1.5 m at
height where conductor
leaves EUT but at
minimum height of
0.1 m
Logic cables are moved
to maximise emission
profile
Eurr arrangement is
close to conditions in
which equipment is used
Cable terrnination
Each cable port has a
cable attached to it
One of each type of
peripheral is connected
to the system
One of each type of
peripheral is connected
to the system
Equipment under test
arrangement
* If the maximum dimension of the equipment under test is smaller than 10 % of the measurement distance, a fixed
antenna height of either 1.5 rn or 3 m can be used.
262
GERMAN, NORTH AMERICAN AND JAPANESE EMC STANDARDS
263
Table Al.6.2 Canadian IT EMC limits
Limits of radiated radio noise emissions
Limits of conducted radio noise emissions
Class .,1
C?ass A
Frequency range
Limits at 30 m
Frequency range
Limits
Narrowband
MHz
~ 30.000
> 88.000
dB (reference 1 J.1Vjm)
30
34
MHz
~ 0.450
> 1.600
dB (reference 1 J.1V)
60
73
70
83
> 216.000
~
~
~
88.000
216.000
1 000.000
~
~
1.600
30.000
Broadband
37
Class B
Class B
Frequency range
Limits at 3 m
Frequency range
Limits
Narrowband
MHz
~ 30.000 ~ 88.000
> 88.000 ~ 216.000
> 216.000 ~ 1 000.000
dB (reference 1 J.1Vjm)
40
44
46
MHz
~ 0.450
dB (reference 1 J.1V)
48
61
Regulations
SORj88/475 and CI08.8-M1983
~
30.000
Broadband
Appendix 1.7
Electrical safety and electroIIlagnetic
radiation safety
Table A1.7.1 Typical regulations on product safety
Standard
Description
IEC950
}
EN60950
CSA22.2 No950
UL1950
Safety of inforn1ation
technology equipmnt
including electrical business
equipment
ULl14
}
UL478
CSA22.2 No154
CSA22.2 No220
Older standards
IEC380
}
VDE0806
CSA22.2 No143
BS6301
ZHl/618 (BG)*
IEC601-1
VDE0750
BS5724
IEC204
VDEOl13
BS2771
IEC65
VDE0860
IEC335
VDE0700
BS3456
Safety of office equipment
Telecom equipment
Safety of video displays and
computers
}
}
Safety of medical prod ucts
Safety of industrial
equipment
Safety of household
appliances
*BG Injuries Insurance Institute (Germany)
264
ELECTRICAL SAFETY AND ELECTROMAGNErrIC RADIATION SAFETY
265
Table Ai.7.2 Examples of standards limiting exposure of hutnans to RF radiation
NCMDRH US [4J Public Law 90-602:
ANSI (1982) [35J (under revision):
Limits for ionising and nonionising radiation
American National Standard C95.1 (Safety levels with respect to
human exposure to radiofreq uency electromagnetic fields)
NRPB (1986) Consultative document [36J
NRPB (1989) GS--11 [37J
DEF-STAN 59/41 (part 3) [3J
MoD (PE) Code of practice (1982): calls up STANAG 2345
DEF-STAN 05-74/1 (1989) [38J
INIRIC (1984) Guidelines: reissued in 1988 [39J
The EEC has introduced regulations regarding nonionising radiation limits under Articles 4 and 5 [40J
[References relate to Chapter 2]
Table Ai.7.3 N RPB GSii recommendations: derived reference levels for exposure to electromagnetic fields atjrequencies
below 300 GHz
Frequency
Hz
< 100
0.1-1 k
1--30 k
0.03-1 M
1--10 M
10---30 M
Root-mean-square values
Electric field strength
Magnetic field strength
Magnetic flux density*
Vim
614,0001f (Hz)
614/f (kHz)
614/f (kHz)
(kHz)
6
6141f (MHz)
61.4/f(MHz)
A/m
1630
163/f(kHz)
163/f(kHz)
4.89If(MHz)
4.89/f(MHz)
4.89/f(MHz)
mT
below 30 MHz: electric and magnetic fields are
Frequency
Hz
30-400 M
0.4-2 G
2-300 G
2
0.2/f(kHz)
0.2/f~kHz)
6.10- /f(MHz)
6.10- 3 /f(MHz)
6.10- 3 /f(MHz)
considered
Root-mean-square values
Electric field strength
Magnetic field strength
Power density
Vim
61.4
97.1v!f (GHz)
137
A/m
0.163
0.258v!f (GHz)
0.364
W/m
10
25,[(GHz)
50
Frequencies above 30 MHz: electric field
alternatives under far-field conditions
2
and power density are taken as equivalent
Appendix 1.8
Military EMC standards
Table Al.B.l Classes of equipment for determining applicable test requirements
Class
Description
I
Communication-electronic (CE) equipment: any item, including subassemblies and parts,
serving functionally generating, transnlitting, conveying, acquiring, receiving, storing, processing
or utilising information in the broadest sense. Subclasses are:
IA
Receivers using antennas
IB
Transmi tters using antennas
IC
Nonantenna CE equipment
counters, oscilloscopes, signal generators, and other electronic
devices working in conjunction with classes IA and IB)
ID
Electrical and electronic equipment and instruments which would affect mission success or
if degraded or malfunctioned by internally generated interference or susceptibility to external
fields and voltages
II
Noncommunication equipment. Specific subclasses are:
IIA
Noncommunication electronic equipment: equipment for which RF energy is intentionally
generated for other than information or control purposes. Examples are medical diathermy
equipment, induction heaters, RF power supplies and uninterruptible power units
lIB
Electrical equipment: electric motors, hand tools, office and kitchen equipment
IIC
Accessories for vehicles and engines: electrically and mechanically driven and engine electrical
accessories such as gauges, fuel pumps, magnetos and generators
Applicable only to accessories for use on items of Classes IlIA and IIIB.
III
Vehicles, engine driven equipment
IlIA
rfactical vehicles: armoured and tracked vehicles, off-the-road cargo and personnel carriers,
assault and landing craft, alnphibious vehicles, patrol boats, and all other vehicles intended for
installation of tactical CE equipment.
IIIB
Engine generators: those supplying power to, or closely associated with CE equipment.
IIIC
Special-purpose vehicles and engine driven equipment: those intended for use in critical
communication areas such as airfields, missile sites, ships' forward areas or in support of tactical
operations.
IIID
Administrative vehicles of basically civilian character not intended for use in tactical areas or in
critical areas covered by Class IIIC, and not intended for installation of communication
equipment.
IV
Overhead power lines
266
MILITARY EMC STANDARDS
267
Table A1.8.2 MIL STn 461 test requirements applicable to equipment classes
Equipmen t class
rrest
RE01
RE02
RE03
RE04
IA
IB
IC
ID
IIA
lIB
IIC
III
A
III
B
CE03
CE04
CE05
CE06
RSOI
RS02
RS03
RS04
CSOI
CS02
CS03
CS04
CS05
CS06
CS07
CS08
IV
• • •
•
RE06
CE02
III
D
• • •
•
• • • • • • •
•
• • •
•
RE05
CEOI
III
C
• • • •
• • • •
• • • •
• • • •
• • • •
• •
• • • •
• • • •
• • • •
• • • •
• • • •
• • • •
•
•
•
•
•
•
• • • •
•
•
•
•
•
•
• • • • •
•
• •
Description of
test method
30 Hz to 30 kHz,
magnetic field
14kHz to 10GHz,
electric field
10 kHz to 40 GHz,
spurious and
harmonics
20 kHz to 50 kHz,
magnetic field
150 kHz to 1 GHz,
vehicles and engine
driven eq.
overhead power
line test
30 Hz to 20 kHz,
power leads
30 Hz to 20 kHz,
con trol and sig. leads
20 kHz to 50 MHz,
power leads
20 kHz to 50 MHz,
con trol and sig. leads
30 Hz to 50 MHz,
inverse filter method
10kHz to 12.4GHz,
an tenna terminal
30 Hz to 30 kHz,
magnetic field
mag. induction field
14kHz to 10GHz,
electric field
14 kHz to 30 MHz
30 Hz to 50 kHz,
power leads
50 kHz to 400 MHz,
power leads
30Hz to 10GHz,
intermod ulation
30Hz to 10GHz, rej.
of undesirable sig.
30Hz to 10GHz,
cross-modulation
spike, power leads
sq uelch circuits
30Hz to 10GHz, rej.
of undesira ble sig.
268
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
Table Al.8.3 Equipment and subsystem classes and applicable parts of MIL STD 461BjC
Class
Description
A
Equipments and subsystems which must operate compatibly when installed in
critical areas, such as the following platforms or installations:
Al
Aircraft (including associated ·ground support equipment)
2
A2
Spacecraft and launch vehicles (including associated ground support
equipment)
3
A3
Ground facilities
4
A4
Surface ships
5
A5
Submarines
6
B
Equipments and subsystems which support the Class A equipments and
subsystems but which will not be physically located in critical ground areas.
Examples are electronic shop maintenance and test equipment used in noncri tical areas;
7
C
Miscellaneous, general purpose equipments and subsystems not usually
associated with a specific platform or installation. Specific items in this class are:
Cl
Tactical and special purpose vehicles and engine driven equipment
8
C2
Engine generators and associated components, uninterruptible power sets and
mobile electric power equipment supplying power to or used in critical areas
9
C3
Commercial electrical or electromechanical equipment
Applicable part
and mobile, including tracked and wheeled vehicles)
10
Table Al.8.4 Test changes between MIL STD 461A
and 461B
Table Al.8.5 [IK RRE 6405 classes of equipment
CE05
RE06
RE05
RE04
CE02
CE04
CS08
RS04
CE07
Class
Description
A
Receivers using antennas
B
rrransmitters using antennas
C
Nonantenna equipment, such as
counters, test equipment, lasers,
computers, power supplies, digital
eq uipmen t, and other electronic devices
working in conjunction with classes A
and B
D
Electronic equipment and instruments
which would affect mission success or
if malfunctioned or degraded by
EM interference, SUCfl as autopilots,
flight instruments, and control devices.
CS09
UM03
UM04
UM05
Deleted from 461 B
Deleted from 461 B
Replaced with UM03
Deleted from 461 B
Combined with CE01
Combined with CE03
Deleted from 461 B
Deleted from 461 B
Power leads, time dcnnain in trod uced
461B
Structure (comm. mode) introduced
461B
Tactical and special vehicles (replaced
RE05), introduced 461B
Engine generators and related,
introduced 461 B
Common elec. and mech. equipments,
introduced 461 B
MILITARY
EMC~
STANDARDS
269
Table Al.8.6 RRE6405 list oj tests
Identification
Equipment
class
EMC parameter
Aspect
Frequency, Hz
RCE01
RCE02
RCE03
RCE04
RCE05
RCE06
RCE07
RCE08
RCE09
RCE10
RCEll
RCE12
RCE13
RCEl4
A-D
A-D
A-D
A-D
A--D
A-D
A-D
A,B
A,B
A,B
A,B
A,B
A,B
A-D
DC power leads, current, AF
AC power leads, current, LF
All leads, voltage, narrowband
All leads, voltage, broadband
Signal and control leads, current
All leads, current, narrowband, HF
All leads, current, broadband, I-IF
Antenna terminals, narrowband, SHF
Antenna terminals, broadband, SHF
Antenna terminals, narrowband,
Antenna terminals, broadband,
Ant. term, narrowband, key down
Ant. term, broadband, key down
Transient emission
20 - 50k
10 k- 50 k
50 k-100 M
50 k-100 M
20 - 50k
50 k-lOO M
50 k-100 M
10 k-100 M
10 k-lOO M
0.1 G- 40G
0.1 G- IG
10k- 40G
0.1 G- 40G
Spikes
RCS01
RCS02
RCS03
RCS04
RCS05
RCS06
RCS07
RCS08
RCS09
RCS10
A-D
A-D
A,C
A,C
A,C
A,C
A,C
A,C
A-D
A-D
DC power leads
DC and AC power leads
Two-signal intermodulation, HF
Two-signal intermodulation, SHF
Rejection of undesired signals, HF
Rejection of undesired signals, SHF
Cross modulation, HF
Cross modulation, SHF
DC and AC power leads
Post-detector rejection
20 - 50k
50 k-400 M
20 -100M
0.1 G- 40G
20 -100M
0.1 G- 40G
20 -100M
0.1 G- 40G
Spikes
20 - 40G
RREOl
RRE02
RRE03
RRE04
RRE05
RRE06
RRE07
RRE08
RRE09
A,B,C
A,B,C
A--D
A-D
A-D
A-D
B
B
A-D
Magnetic field, LF
Magnetic field, HF
Electric field, narrowband, HF
Electric field, broadband, HF
Electric field, narrowband, SHF
Electric field, broadband, SHF
Antenna, spurious, narrowband
Antenna, spurious, broadband
Transien t emission
30k
20
30k- 3M
14 k-lOO M
14 k-100 M
0.1 G- 40G
0.1 G- IG
0.1 G- 40G
0.1 G- 40G
Spikes
RRS01
RRS02
RRS03
RRS04
A---D
A--D
A-D
A-D
Magnetic field, LF
Magnetic field, induction
Electric field, HF
Electric field, SHF
50k
20
Spikes
14 k-lOO M
0.1 G- 40G
RMP01
RMP02
RMP03
RMP04
B
B
A,B
A
Occupied bandwidth, transmitter
Frequency tolerance, transmitter
Antenna pattern, far field
Receiver, bandwidth
1.0M1.0 M0.1 G0.1 G-
40G
40 G
40G
40G
270
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
Table A1.B.7 RRE6405 EM C' grading by environlnental conditions
Grade
Shipboard
Air service
Land service
L
Equipment used outside the
metal hull and/or metal
superstructure of surface
ships, or above decks only in
any ship which is of metallic
construction, or in any ship
which is not of metallic
construction
Equipment for use generally
in civil and military aircraft
Equipment sited not within
2 m of another equipment
that emits, or is susceptible to,
electromagnetic radiation
M
Not used
Not used
Equipment sited not within
15 m of another equipment
N
Equipment used on board
submarines and within the
metal hull and /or
superstructure of surface ships
Not used
Equipment sited not within
100 m of another eq uipn1en t
Table A1.B.B DEF STAN 59-41 EMC' tests
Test
reference
Test description
Service*
a pplicabili ty
DCEOI
DCE02
DCE03
Signal/controlline~ current
Power line, current 20 Hz-ISO MHz
20 Hz-ISO MHz
Exported transients, power lines
Land sea air
Land sea air
I-land
aIr
DREOI
DRE02
DRE03
E-field radiation at 1 m 14kHz-18GHz
H-field radiation at 70 mm 20 Hz-50 kHz
E-field radiation, installed antenna 1--76 MHz
Land sea air
Land sea air
Land
DCSOI
DCS02
DCS03
DCS04
DCS05
DCS06
DCS07
Power line, voltage 20 Hz-50 kHz
Power, control and signal leads 50 kHz-400 MHz
Control/signal, current 20 Hz-50 kHz
Imported transient susceptibility
Externally generated transients
Imported long transient susceptibility 28 V systems
Imported short transient susceptibility
I-Jand sea air
Land sea air
Land sea air
aIr
sea
Land
Land
DRSOI
DRS02
H-field at 50 mm 20 Hz-50 kHz
E-field, 14kHz-18GHz
Land sea air
I-Jand sea air
DMFSOI
Magnetostatic field
Land sea
* Check individual limits for actual frequency range
DCE conducted en1ission
DCS
conducted susceptibility
DRE
DRS radiated susceptibility DMFS magnetostatic field susceptibility
radiated emission
Appendix 1.9
COlnpendiuln of EMC and
related standards
With limited space this compendium cannot be
exhaustive of all standards and specifications related
to EMC and electrical safety worldwide. Regulations
and standards are changing frequently as the field
develops rapidly owing to technical advances,
economic and political factors. However, this list
contains sufficient examples of EMC standards to
provide a starting point for further exploration.
BS 5406 (1988): Limitation of disturbances in
electricity supply networks caused by domestic
and similar appliances equipped with electronic
devices (IEC 555)
BS 5602 (1978): Code of practice for the
abatement of RFI from overhead power lines
(CISPR 18)
BS 5750 Series: Quality assurance related
standards
BS 5783 (1984): Code of practice for handling
electrostatic devices
BS 6021 Part 3 (1982): Specification for fixed
capacitors used for RFI suppression: General
requirements and methods of test (IEC 384-14)
BS 6299 (1982): Measurement methods for passive
suppression filters and components (CISPR 17)
BS 6345 (1983): Methods of measurement of RFI
terminal
voltage
of
lighting
equipment
(CISPR 15)
BS 6491 (1984): Part 1 ESD
BS 6527 (1988): Specification for limits and
measurements
of
RFI
characteristics
of
information technology equipment (CISPR 22),
(VDE 08781)
BS 6651 (1985): Protection of structures against
lightning
BS 6656 (1986): The prevention of inadvertent
ignition of flammable atmospheres by RF
radiation (read with HSE GS21 HMSO 1983)
BS 6657 (1986): Prevention of inadverten t ignition
of EEDs by RF radiation (read with OB. Procs
42413 and 42202)
BS 6667 (1985): Electromagnetic compatibility
requirements for industrial process control
Part 1 General introduction (IEC 801-1)
Part 2 Susceptibility to ESD (IEC 801-2)
Part 3 Susceptibility to radiated EM energy
(IEC 801-3)
Part 4 Electrical fast transient/burst require
ments (IEC 801-4)
Part 5 Surge immunity requirements (draft in
1990)
BS 6839 (1987): Part 1 Specification for
communication and interference limits and
measurements for mains signalling equipment
Part 2 - Specification for interfaces for mains
signalling equipment
BS 3G 100 (1980): Part 4 section 2: EMI at radio
1 UK British Standards (EMC)
BS 613 (1977): Specifies components and filter
units for EMI suppression
BS 727 (1983): Specification for RFI measurIng
apparatus (CISPR 16)
BS 800 (1988): Specification of RFI limits and
measurements for household appliances, portable
tools and other electrical equipment (CISPR 14),
(VDE 0875)
BS 833 (1985): Specification of RFI limits and
measurements for electrical ignition systems of
internal combustion engines (CISPR 12)
BS 905 (1985): Specification of EMC for sound
and TV receivers and associated equipment
Part 1:
Specification
of limits
for
RFI
(CISPR 13), (VDE 0872)
Part 2: Specification of limits for immunity
(CISPR 20)
BS 1597 (1985): Specification for limits and
methods of measuring electromagnetic interference from marine equipment and installations
BS 2316 Parts 1 and 2 (1981): General requirements and tests for radio frequency cables
BS 4727 Part 1 Gp 9 (1976): Glossary of technical
terms
connected
with
radio
interference
technology (IEC 50 Ch. 902)
BS 4809 (1981): Specification of RFI limits and
measurements for RF heating equipment
(CISPR 11), (similar to VDE 0871)
BS 5049 (1981): Methods of measurement of RF
noise from power supply apparatus working
above 1 kV (CISPR 18)
BS 5260 (1981): Code of practice for RFI
suppression on marine installations
BS 5394 (1988): Specification of limits and
measurement methods for RFI characteristics of
fluorescent lamps and luminaires (CISPR 15),
(VDE 0875)
271
272
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
and audio frequency
requirements for
equipment for use in aircraft
BS G229: Specification of environments for
equipment for use in aircraft (DO 160)
NWM 0320: UK National weights and measures
standards on EMC for metrology equipment
2 UK British Stand·ards (electrical
safety)
BS 2754: Protection against electric shock
BS 2771: Electrical safety of industrial machines
BS 3192: Electrical safety of radio and TV transmitters
BS 3456: Household safety
BS 5458: Safety requirements for electrical
indicating and recording equipmen t
BS 5724: Safety of mechanical equipment
BS 6301: Safety of telecommunications apparatus
3 UK NAMASjNPL docutnents
NAMAS M3: Concise directory of approved
calibration and testing laboratories
NAMAS MI0: General criteria of competence for
calibration and testing laboratories
NAMAS MIl: Regulations to be met by
calibration and testing laboratories
NAMAS M 13: Regulation concerning the use of
the NAMAS logo/mark
NAMAS M16: The quality manual - guidance
for preparation
NAMAS NIS20: Uncertainty of measurement for
NAMAS electrical product testing laboratories
NAMAS B3003: Expression of uncertainty In
electrical measurements
NPL 0004/8K/NJ /6/90: NPL Points of contact
NPL 007/J.5K/NJ/9/90: RF and mIcrowave
measurement services
4 CISPR EMC standards
CISPR 1: RFI measuring set 0.15-30 MHz
CISPR 2: RFI measuring set 25-300 MHz
CISPR 3: RFI measuring set 10-150 kHz
CISPR 4: RFI measuring set 300 MHz-IGHz
CISPR 5: Peak, quasipeak and average detectors
CISPR 1-6: inclusive have been superseded by
CISPR 16
CISPR 7: Recommendations of CISPR (including
recommend a tion
19: Limits in large-scale
production)
CISPR 8: Reports and study questions
CISPR 9: CISPR and national limits
CISPR 10: Organisation, rules and procedures of
CISPR (1981 and 1983)
CISPR 11: ISM limits and measurements (1975,
1976)
CISPR 12: Ignition limits and measurements
(1978,1985)
CISPR 13: Sound and TV receivers limits and
measurements (1975, 1983)
CISPR 14: Household equip. limits and measurements (1985)
CISPR 15: Fluorescent lamps and luminaires
limi ts and measurements (1985)
CISPR 16: RFI measuring sets specification and
measurements (1977, 1980, 1983)
CISPR 17: Filters and suppressors measurement
(1981 )
CISPR 18: RFI of power lines and HV equipment
Part 1 description (1982)
CISPR 19: Microwave ovens measurements
above 1 GHz (1983)
CISPR 20: Immunity of sound and TV receivers
(1985)
CISPR 21: Interference to mobile radiocommunications (1985)
CISPR 22: IT equipment limits and measurement
(1985)
CISPR 23: Derivation of limits for ISM
5 Gertnan VDE EMC and electrical
safety standards
5.1 VDE EMC standards
VDE 0565: Specification for RFI suppression devices
Part 1 capacitors
Part 2 chokes
Part 3 filters (up to 16A)
Part 4 ceramic capacitors
VDE 0839: Teil 10 generators ESD
VDE 0843: Part 2 ESD identical with IEC 801-2
VDE 0846: Teil 11 test generators ESD
VDE 0871: Limits of RFI from RF apparatus and
ins tallations
Part 1 ISM
Part 2 EDP
VDE 0872: Interference suppression for radio and
TV receivers
VDE 0873: RFI from electrical utility plants and
HV systems
VDE 0874: Recommendation for RFI suppression
VDE 0875: RFI from appliances (below 10 kHz)
Part 1 household appliances
Part 2 fl uorescent lighting
Part 3 appliances with motors
VDE 0876: Interference measuring apparatus
Part 1 weigh ted indication
Part 2 disturbance analyser
Part 3 current probes
VDE 0877: RFI measurement procedures
Part 1 interference voltage
Part 2 interference field strength
Part 3 interference on power leads
COMPENDIUM OF EMC AND RELATED STANDARDS
VDE 0879: RFI suppressIon for motor vehicles
and engines
DIN 43 305 pt. 302: Methods of measurement on
radio receivers for various classes of emission:
Methods of measurement for checking the
immunity from. interference fields of radio
receivers. Beuth Verlag, Berlin
5.2 VDE safety standards
VDE 0113: Safety of industrial equipment (IEC
204)
VDE 0700: Safety of household appliances (IEC
335)
VDE 0750: Safety of medical equipment (IEC
601 )
VDE 0806: Safety of office equipment (IEC 380)
VDE 0806: Safety of household appliances (IEC
065)
VDE 0848: Hazards by electromagnetic fields
ZH 1/618 (BG): Safety of video displays, etc
6 European and international
standards
EMC standards and specifications in force in
Europe and most countries in the world are listed
in the following publication: 'Electromagnetic
compatibility
regulations
and
standards
worldwide', Netderlands Normalisatie lnstitut
(UDC 621.391.82(100))
273
(CISPR 14, BS 800, VDE 0875, FCC Pt15: near
equivalent)
EN 55015: Limits and measurement methods for
RFI characteristics of fluorescent lamps and
lurninaires (CISPR 13, BS 5394, VDE 0875)
EN 55020: Immunity of sound and television
broadcast receivers and associated equipment in
the frequency range 1.5 to 30 MHz by current
injection method (CISPR 20, BS 905 Pt2)
EN 55022: Limits and methods of measurement of
the RFI emission characteristics of information
technology equipment (CISPR 22, BS 6527)
EN 55101-4: RF immunity of information
technology eq uipmen t (in draft)
EN 60555-2: Disturbances in supply systems caused
by household appliances and similar electrical
equipment - harmonics (lEe 555, BS 5406)
EN 60555-3: Disturbances in supply systems
caused by household appliances and similar
voltage fluctuations
electrical eq uipment
(IEC 555, BS 5406)
EN 60950: Safety of information technology and
business eq ui pmen t
HD 481: Immunity to RF, ESD, transients and
surges of industrial process control equipment.
Basic standard. (IEC 801, BS 6667)
HD 481.1 S 1: General introduction
HD 481.2 S 1: Method of evaluating susceptibility
to electrostatic discharge
HD 481.3 S 1: Method of evaluating susceptibility
to radiated electromagnetic energy
6.1 European harmonised standards
EN 29000: Quality assurance of calibration and
testing laboratories
EN 45001: General req uiremen ts for technical
competence of testing laboratories
EN 50065-1: Mains signalling on low-voltage
electrical installations
EN 50081-1: Generic RFI emission standard for
any equipment in the domestic, commercial and
light industrial electromagnetic environments
(class 1 environments)
EN 50082-1: Generic RF immunity standard for
any equipment in the domestic, commercial and
light industrial electromagnetic environments
(class 1 environment)
EN 55011: Limits and methods of measurement of
RFI characteristics of ISM equipment (excluding
diathermy apparatus)
(CISPR 11, BS 4809,
VDE 0871, FCC Pt18: near equivalent)
EN 55013: Limits and measurement methods for
RFI characteristics of sound and television
broadcast receivers (CISPR 13, BS 905 Ptl,
VDE 0872, FCC Pt15: near equivalent)
EN 55014: Limits and methods of measurement of
RFI characteristics of household electrical
appliances, portable tools and similar equipment
6.2 Other European standards
UN ECE Reg. 10: Control of RFI from motorcycles and vehicles with 3 or more wheels
72/245/EEC: Suppression of motor vehicle ignition
(CISPR 12, BS 833)
71/320/EEC: Vehicle brakes
UN ECE Reg. 13/05: Vehicle brakes
EEC Directive 71/320/EEC (amended 85/647/
EEC): Braking devices
EEC 451 7/79: Contains reference to ESD
ECMA Standard 47: Limits and measurement
methods for radio interference from EDP
equipment. European Computer Manufacturers
Association, Geneva, Switzerland
ECMA TR/40: ESD testing of IT equipment ---technical report
6.3 lEe standards related to EMC
IEC 50: International electro technical vocabulary,
Chapter 161 on electromagnetic compatibility
IEC 96: Part 0 Guide to the design and
detailed specification of RF cables
Part 1 - General requirements and measurement
methods for RF cables
.
274
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
IEC 106: Recommended methods of measurement
of radiated and conducted interference from
receivers induced by AM, FM and TV broadcast
transmissions
IEC 478: Part 3 - RFI tests for DC stabilised
power supplies
IEC 533: EMC of electrical and electronic
equipment in ships
IEC 555: Disturbances in supply systems caused
by household appliances and similar equipment
IEC 654: Operating conditions for industrial
process measurement and control equipment
IEC 801: EMC requirements for industrial process
control instrumentation
IEC 801-1: General introduction
IEC 801-2: Susceptibility to ESD
IEC 801-3: Susceptibility to radiated EM
energy (draft)
IEC 801-4: Electrical
fast
transients/burst
req uirements
IEC 801-5: Surge immunity requirements (draft)
IEC 801-6: Immunity to conducted RF disturbances above 9 kHz (draft)
6.4 lEe standards related to electrical
safety
IEC 065:
0860)
IEC 204:
0113)
IEC 335:
0700)
IEC 380:
IEC 601:
Safety of household appliances (VDE
Safety of industrial equipment (VDE
Safety of household equipment (VDE
Safety of office equipment (VDE 0806)
Safety of medical products (VDE 0750)
6.5 ISO publications
ISO 9000: Quality assurance aspects of testing
ISO Guide 25: Technical competence of testing
laboratories
ISO/TC22/SC3/WG3
paper N 260:
Road
vehicles: Electrical in terference from electrostatic discharge
INIRC/IRPA (1988): Guidelines on limits of
exposure to radio frequency electromagnetic fields
in the frequency range from 100 kHz to 300 GHz
7 US EMC regulations and standards
FCC Code of Federal Regs. Title 47 volumes 1-5
(docket 20780)
FCC Part 15: Electromagnetic compatibility ofRF
devices
Subpart A General
Subpart B Administrative procedures
Subpart C Radio receivers
Subpart D General requirement for low-power
communications devices
Subpart E Low-power communications devices
(specific devices)
Subpart F Field disturbance sensors
Subpart G Auditory assistance devices
Subpart H TV interface devices
Subpart I Measurement procedures
Subpart J Computing devices
FCC Part 18: Electromagnetic compatibility of
ISM equipment
Subpart A General information
Subpart B Applications and authorisations
Subpart C Technical standards
FCC Part 68: Electromagnetic compatibility of
equipment to be connected with the telephone
network
FCC Doc. OCE44: Open-field site calibration
(horizon tal polarisation)
OST 62:
Understanding
the
FCC
EDP
regulations
OST 55: Open-field sites for FCC testing
MP4 Uuly 1987): FCC measurement procedures
for EDP
SAE J 551 C : Vehicle ignition interference
SAE J 1113 (1984): Susceptibility procedures for
vehicle components (except aircraft)
SAE J 1338 (1981): Open-field whole-vehicle
radiated susceptibility testing
SAE J 1407 (1982): TEM cells for automotive
susceptibility tests
SAE J 1507: Apparatus and test procedures for
whole-vehicle susceptibility testing
SAE ARP 936: ~1easurement of capacitors
SAE ARP 937: Jet engine EMI
SAE ARP 958: Test antenna calibration practice
SAE Jl113 (1989) Part 5: Electromagnetic compatprocedure for vehicle
ibility measurement,
components: Susceptibility to ESD
SAE J1338
SAE J1407
SAE J1507
SAE AIR 1147: Precipitation of static radio interference from jet engine charging
SAE AIR 1499: Recommendations for commercial
EMC susceptibility standards
ANSI C16: EMC aspects of communication and
electronic equipment
ANSI C63: Measurement techniques for EMC
C63.2: Specification for EMI and field strength
ins trumen tation
C63.4 (1988) EMC: Radio noise emissions from
low voltage electrical and electronic equipment
10 kHz-1 GHz
ANSI C68: EMC aspects of high-voltage testing
techniques
ANSI C95.1 (1982): Safety levels with respect to
human exposure to RF EM fields (300 kHz100 GHz)
ANSI April 1989 (draft 5): Guide for ESD test
COlvIPENI)IUM OF EMC AND RELA1'EI) STANDARDS
methodologies
and
cri teria for
electronic
equipment
UL 1950: Safety of IT and electrical business
equipment
MDS-201-0004 (1979): EMC standard for rnedical
devices. A voluntary code
AAMI (
:' Heart pacemaker EMC voluntary
standard
FDA Infant Apena Monitor Standard
Mandatory EMC regulation applied to these
devices
NCMDRH (US Public Law 90-602, 1968): Safe
radiation limits from TVs, x-ray machines,
microwave ovens, etc
IEEE S302: Standard method for measuring EM
field strength below 1000 MHz in radiowave
propagation
IEEE S299: Measuring shielding effectiveness of
high-performance shielded enclosures
IEEE S473 (1985): Recommended practice for an
electromagnetic site survey (10 kHz-1 0 G Hz)
IEEE S518: Guide on the installation of electrical
equipment to minimise interference to controllers
from external sour'ces
IEEE ad hoc committee, 1990: Proposed new code
of ethics, vol.
no.3, p.5
US Safety Standard NFPA-STD-70-1971: Electric
wiring and other devices
8 Exam.ples of other EMC
regulations
veCI (1986) Japan: 1'he control of
netic emissions from electronic data
and office machines (Voluntary Code establishes
limits and test methods)
SOR/88-475 (1988) Canada: Radio interference
regulations amendment
CSA C108.8-M1983 Canada:
EMC
procedures
CSA 22.2 no.154: Safety of
and electrical
business equipment
For further examples of worldwide
regulations, see 1'able 2.1 in
2
9 US m.ilitary standards (EMC)
MIL S1-'D 188: Military communications systems
tactical standards
MIL STD 188-125 (draft
1989): NEMP
testing
MIL STD 220: Insertion-loss measurements of
components
MIL STD 285: Attenuation measurement method
for shielded enclosures
MIL STD 331A: Contains
MIL STD 454: General rpnlllll~""YY'lPY\t-C'
equipment
275
MIL STD 46
interference characteristics requirements for
MIL STD 462:
characteristics, measurement of
MIL STD 463:
Electromagnetic
interference
characteristics, definitions
systems of units
MIL STD 469: EMC - radar engineering
MIL STD 481A: Antenna: method of calibration,
(para
MIL STD 704: Electric power, aircraft characteristics and use
MIL STD 826A: 'Transients:
a 10 JiF '-'.....,I--J(A,'--'~ 'J~
MIL STD 831: Preparation of test reports
MIL STD 833C: Involves aspects of ESD
MIIJ STD 1310:
and grounding methods
on board
for EMC and safety
MIL STD 1337: General suppression and system
req uirements for electric
hand
tools (ships)
MIL STD 1344A: Method 3008 (1980): "--JJ"~~'~~'-A~'"J.;;;"
effectiveness of multicontact connectors
MIL STD 1377: Effectiveness of
connector
and weapon enclosure shielding and filters in
precluding
EM
hazards
to
measurement of,
MIL STD 1385: Preclusion of ordnance hazards
in EM fields, general
MIL STD 1512:
initiated,
req uirements
MIL STD 1541:
for space
systems
MIL STD 1542: EMC and
ments for space systems facilities
MIL STD 1857:
...
MIL-B-5087: Bonding, electrical
\.J",,-/vL~.'J.LJ. for aerospace systems
MIL-W -5088:
installed
MIL-E-6051D:
electromagnetic
~" OJ"LL~",
MIL-E-55301
MIL-I-16910C
MIL-I-6181D
MIL-M-3851 O-ESD
MIL-W-83575:
design and
AFSC DR 1-4:
netic
t-~
v'JAJ.l.
r>"1"Yl
t--J(A, ...
y-,.r-.
10 UK tnilitary standards
DEF STAN 00-10: Part 2, section 4
DEF STAN 00--35:
I)EF
DEF STAN 07-55 and AvP
Part 2
of service
r/"'''''",,''"¥>
" " Y \ ' ! T1
electro00-1,
"",.Y\ TO
276
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
Part 4 natural environments (lightning)
Part 5 ind uced environmen ts
DEF STAN 08-4: Nuclear weapons explosion
effects and hardening
DEF STAN 08-5: Superseding AvP 32 'Design
requirements for guided weapons'
DEF STAN 59-41 (June 1988): Electromagnetic
compatibility
Part 1 general req uiremen ts
Part 2 management and planning procedures
Part 3 technical requirements (test methods
and limits)
Part 4 open-site testing
Part 5 technical req uiremen ts for special EM C
test equipment
DEF STAN 61-5:
Part 1 terminology and definitions
Part 2 ground generating set characteristics
Part 4 power supplies in warships
Part 5 ground power supplies for aircraft
servIcIng
Part 6 28 V DC electrical systems in military
vehicles
NWS 2: EMC aspects of cabling in ship installations
NWS 3 (1985): Electromagnetic compatibility of
naval electrical equipments
NWS 1000 (1986): Requirements for naval
weapon equipment
Part 1, chapter 5, section 10 Electro-
magnetic compatibility design guide for naval
weapons platform (refers also to Part 2)
NES 529: Nuclear hardening guide
NES 1006 (1988): Supersedes NWS 6, Radio
frequency environment and acceptance criteria
for naval stores containing EEDs
BR 2924: Radio hazards in naval service
BR 8541: Safety req uirement for armament stores
for naval use
MVEE 595 (1975): Electromagnetic interference
and susceptibili ty req uiremen ts for electrical
equipments and systems in military vehicles
(forms part ofDEF STAN 59-41)
RRE 6405 (1974): Requirements for electromagnetic compatibility of electronic equipments
Part 1 guide
Part 2 req uirements
Part 3 measurement techniq ues
,
AVP 118: Guide to electromagnetic compatibility
in aircraft systems
STANAG 1307: (Implement by NESI006)
STANAG 4234: RF environmental conditions
affecting the design of material for use by NATO
forces
MoD (PE) 1982: Intense radio frequency
radia tion code of practice
STANAG 2345: RF exposure limits for personnel
NRPB (1986): Advice on RF safety
NRPB GS11 (1988): Guidance on RF exposure
Appendix 2.1
Modulation rules
Table A2.2 DEF STAN 59-41 modulation rules
Table A2.1 MIL STD 462 (N3) modulation rules
For communications equipment
(a) AM receivers: modulate with 500/0 1 kHz
sinusoid
(b) FM receivers: When monitoring signal-tonoise ratio, modulate with 1 kHz signal and
10kHz deviation
(c) SSE receivers: No modulation
(d) Other equipments: As for AM receivers
Susceptibility
frequency
Modulation
type
Ship and land service use:
20 Hz-50kHz
Equipments with video channels:
Use 90-100 % pulse modulation with
duration of 2/ B Wand repetition rate of
BW/1000, where BW == video bandwidth
Digital equipment:
Use pulse mod ulation with pulse duration
and repetition rates equal to that used in
equipment
CW
50 kHz- 1 G H:z
CW
(a)
(b) AM 100% square
or sine at frequencies
in the range
100 Hz-10kHz
(c) AM 100% square 1 Hz
200 MHz-18 GHz
Pulsed CW, pulse
length 1 j1s, PRF 1 kHz
(for test DRS02 only)
For aircraft use:
20 Hz-50kHz
50kHz-2 MHz
CW
(a)
(b) AM 100% square at
lkHzPRF
2MHz-30MHz
CW
(a)
(b) AM 100% square at
1 kHz PRF
(c) AM 100% square at
1-3 kHz PRF
Nontuned equipment:
AM at 50% with 1 kHz sinusoid
30 MHz--1 GHz
Radiated testing
1-18 GHz
150-225 MHz
580-610 MHz
0.79-18 GHz
277
CW
CW
(a)
(b) AM 100% square at
1kHzPRF
(a)
CW
(b) A complex modulation
of pulse (1 j1s) and
AM (0.5Hz)
Appendix 3.1
NAMAS-accredited laboratories
Lucas Aerospace Ltd.
Power Systems Division
Maylands Avenue
Hemel Hempstead
Herts HP2 4SP
01442 242233
As given in the EMC Awareness Campaign
brochure (Reference 11 Chap. 13).
British Telecom
Product Evaluation Section (MC2)
Materials and Component Centre
310 Bordesley Green
Birmingham B9 5NF
0121 771 6007
BSI Testing
Unit 5
Finway Road
Hemel Hempstead
01442 233442
Matra Marconi Space UK
Environmental Engineering and Test Lab
Anchorage Road, Portsmouth
Hampshire P03 5PU
01705 674554
National Weights and Measures Laboratory
Stanton Avenue
Teddington
Middlesex TW 11 OJZ
0181 943 7242
HP2 6PT
Chomerics (UK) Ltd.
Parkway
Globe Park Industrial Estate
Marlow, Bucks SL7 1YB
01628 486030
Thorn EMI Electronics Ltd.
Sensors Division
Manor Royal, Crawley
West Sussex RHI0 2PZ
01293 528787 x4985
Cranage EMC Testing
Stable Court
Oakley
Market Drayton
Shropshire TF9 4AG
01630 658568
Other NAMAS-accredited test laboratories (listed
in the NAMAS Concise Directory) follow.
Apologies to those laboratories which may not
have been included. Prospective users of an
accredited EMC test laboratory should consult
the most up-to-date NAMAS directory for details.
Categories of permanent laboratory:
GEC Marconi Avionics
EMC Test Centre
Maxwell Building
Donibristle Industrial Park
Dunfermline KY11 5LB
01383 822131
0: Permanent laboratory where the calibration or
testing facility is erected on a fixed location for
a period expected to be greater than three years.
I: Site calibration or testing performed by staff
sent out on site by a permanent laboratory that
is accredited by NAMAS.
GPT Ltd.
Environmental Testing Group
New Century Park
PO Box 53,
Coventry CV3 lHJ
01203 562046
AQL-EMC Ltd.
16 Cobham Road
Ferndown Industrial Estate
Poole
Dorset BH21 7PE
01202 861175
British Aerospace (Dynamics) Ltd.
EMC Test House, EME Department
FPC065
PO Box 5
Filton, Bristol BS 12 7QW
0117 9693 866 x6549
ICL
Winsford EMC Laboratory
West Avenue
Kidsgrove, Stoke on Trent
Staffs ST7 1TL
01782 771000 x3772
278
Cat 0 and I
Cat 0
NAMAS-ACCREDITED LABORArrORIES
Chase EMC Ltd.
St Leonards House
St Leonards Road
London SW147LY
0181 878 7747
Cat 0
ERA Technology Ltd.
Electromagnetic Compatibility Division
Cleeve Road
Leatherhead
Surrey KT22 7SA
01372 374151
Cat 0
GEC Avionics Ltd.
Central Quality Department
Airport Works
Rochester
Kent MEl2XX
01634 844400 ext 3540
Cat 0
GEC Ferranti Defence Systems Ltd.
EMC Laboratory
St Andrews Works
Robertson Avenue
Edinburgh EH11 1PX
0131346 3912
279
Cat 0
Hunting Communication Technology Ltd. Cat 0
Electromagnetic Assessment Group
Royal Signals and Radar Establishment
Pershore
W orcestershire WR 10 2RW
01386 555522
Kingston Telecommunication Laboratories Cat 0
Newlands Science Park
Inglemire Lane
Hull
Humberside HU67TQ
01482 801801
Appendix 3.2
Cotnpetent bodies
As given in the EMC Awareness Campaign
brochure (Reference 11, Chap. 13).
Chase EMC Ltd.
St Leonards House
St Leonards Road
London SW147LY
0181 878 7747
Assessmen t Services Ltd.
Segensworth Road
Titchfield
Fareham
Hampshire P0155RH
01329 443322
Dedicated Microcomputers Ltd.
1 Hilton Square
Pendlebury
Manchester M27 IDL
0161 794 4965
AQL-EMC Ltd.
16 Cobham Road
Ferndown Industrial Estate
Ferndown
Poole
Dorset BH21 7PE
01202 861175
EMC Projects Ltd.
Holly Grove Farm
Verwood Road
Ashley
Ringwood
Hampshire BH24 2DB
01425 479979
BNR Europe Ltd.
EMC Engineering Centre
London Road,
Harlow
Essex CM179NA
01279 429531
ERA Technology Ltd.
EMC Department
Cleeve Road
Leatherhead
Surrey KT22 7SA
01372 374151
British Aerospace Defence Ltd.
Dynamics Division
Dept 319, FPC 047, PO Box 5
Filton
Bristol BS 12 7RE
0117 969 3866
GEC Avionics Ltd.
Central Quality Department
Airport Works
Rochester
Kent ME12XX
01634 844400 x8097
British Telecom Research Laboratories
EMC Engineering Group
Martlesham Heath
Ipswich
Suffolk IP5 7RE
01473 642319
Hunting Communications Technology Ltd.
Electromagnetic Assessment Group
R.S.R.E. Pershore
W orcestershire WR 10 2RW
01386 555522
Cambridge Consultants Ltd.
Science Park
Milton Road
Cambridge CB4 4DW
01223 420024
IBM (UK) Ltd.
EMC Laboratory
PO Box 30
Spango Valley
Greenock PA 16 OAH
01475 892000
CF Europe Ltd.
Greencourts Business Park
Styal Road
Moss Nook
Manchester M22 5LG
0161 436 8740
IBM (UK) Ltd.
EMC Laboratory
H ursley Park
Winchester
Hampshire S021 2]N
01962 844433
280
COMPETENT BODIES
Interference Technology International
41-42 Shrivenham Hundred Business Park
Shrivenham
Swindon SN6 8TZ
01793783137
JRS Associates
59 Titchfield Road
Stubbington
Fareham PO 14 2JF
01329 665549
Kingston Telecommunications Labs (KTL EMC)
Newlands Science Park
Inglemire Lane
Hull
Humberside HU6 7TG
01482 801801
MIRA
Watling Street
Nuneaton
Warwickshire CV 10 OTU
01203 348541
Radio Frequency Investigation Ltd.
Dunlop House
Dunlop
Ayrshire KA34BD
01560 83813
Radio Technology Laboratory
Whyteleafe Hill
Whyteleafe
Surrey CR3 OYY
0181 660 8456
Serco Services Ltd.
DMCS EMC Facility
VI Building
RSRE North Site
Leigh Sinton Road
Malvern
Worcestershire WR 14 1LL
01684 592989
OFFER
Electricity Meter Examining Service
Hagley House
Hagley Road
Edgbaston
Birmingham B 16 8QG
SGS EMC Services
The Industrial Estate
St Michael's Way
Sunderland SR 1 3SD
0191 515 2666
Radio Frequency Investigations Ltd.
Ewhurst Park
Ramsdell
Basingstoke
Hampshire RG26 5RQ
01256 851193
TRL Technology Ltd.
Alexandra Way
Ashchurch
Tewkesbury
Gloucestershire GL20 8NB
01689 850438
281
Appendix 3.3
EMC consultancy and training
Organisations offering consultancy and training in
the UK in addition to competent bodies as given
in the EMC Awareness Campaign brochure
(Reference 11 Chap. 13). See also list of organisations identified as shadow UK Competen t Bodies
and list of NAMAS accredited laboratories. Most
offer consultancy, some also provide training.
Salford University Business Services Ltd.
0161 736 2843
Cherry Clough Consultants
01457 871605
*U niversity of Hertfordshire
School of Engineering 01707 279176
Higher Degrees:
MSc in Electromagnetic Compatibility
University of Hull
Department of Electronics Engineering
01482 465891
York Electronics Centre
University of York 01904 432323
U niversi ty of York
Department of Electronics
Paisley University
0141 848 3401
MSc in Electrical and Electromagnetic Engineering
University of Wales
Department of Electrical and
Electronic Engineering
Cardiff 01222874000
*Northern Ireland Technology Centre
Queens University of Belfast 01232 245133
*University of Central England
Birmingham
Faculty of Engineering and Computer Technology
0121 331 5000
*Napier University
Edinburgh
Contact Alexander MacLeod
0131 444 2266
*Huddersfield University
Manufacturing Advice Centre
01484 422288
lEE
Professional' Development
Stevenage 01438 313311
lEE
Distance learning package, in conjunction with
York Electronics Centre 01438 313311
Society of Environmental Engineers
Buntingford 01763 71209
*The John Moore U niversi ty
Liverpool
School of Information, Science and Technology
0151 231 2052
*University of Plymouth
School of Electrical Engineering
01904 432323
Elmac
Chichester
01243 533361
Pera International
Melton Mowbray 01664 501501
01752 232588
Schaffner EMC
Reading 01734 770070
*Highbury College of Technology
Department of Electrical and Electronic Engineering
Portsmouth 01705 383131
Sira Communications (Training)
Chislehurst 0181 467 2636
*Staffordshire U niversity
. Stafford 01785 52331
Sira Test and Certification (Consultancy)
Chislehurst 0181 467 2636
*university of Glamorgan
The Technology Centre
Pontypridd 01443 480480
Surrey Group
Staines 01784 461393
*Denotes regional electronics centre offering EMC
consultancy
Note: many other companies offer EMC traInIng
and consulting; see current EM C trade press
282
Appendix 3.4
Useful publications on EMC
'UK Regulations' (SI 1992/2372) are available
from HMSO and its agents.
CORP, M.B.: 'Zzaap! taming ESD, RFI and
EMI'. (Academic) ISBN 0-12-189930-6
'EMC workbook'. DTI training aid available from
Interference rr echnology International
0793 783137
DENNY, H.W.: 'Grounding for the control of
EMI'. Don White Consultants ISBN 0-93226317-8
'EMC directive and amending directive'. Centre
for European Business Information, Contact:
Steve Terrell 071 828 6201
Also published in the Official Journal of the
European Communities, ref: L139 23 May 1989
GEORGOPOULOS, C.J.: 'EMC In cables and
interfaces'. ICT
European explanatory document on the EMC
Directive, List of competent bodies, Guidance
document on the content of the technical construction file, Product standards booklet on EMC
DTI, 151 Buckingham Palace Road, London
SW1W 9SS
SCHLICKE, H.M.: 'Electromagnetic compatibility: applied principles of cost effective con trol
of electromagnetic interference and hazards'.
(Marcel Dekker) ISBN 0-8247-1887-9
BSI 'EMC manual'
KEISER, B.: 'Principles of electromagnetic
compatibility'. (Artech) ISBN 0-89006-206-4
VIOLETTE,
WHITE
and
VIOLETTE:
'Electromagnetic compatibility handbook'. (Van
Nostrand) ISBN 0-442-28903-0
0908 226888
Bibliography and information pack 1991, lEE
technical information uni t, Coupland and
Fountain
Texts that include rigorous analytical explanations
of electromagnetic phenomena associated with
EMC and which may be suitable for undergraduate or postgraduate study include:
WILLIAMS, T.: 'E~;[C for product designers'.
(Bu tterworth-Heinemann)
PAUL, C.R.: 'Introduction to electromagnetic
compatibility'. (Wiley, 1992)
MARSHMAN, C.: 'A guide to the EMC
directive'. (York Electronics Centre, EPA Press)
GOEDBLOED, J.J.: 'Electromagnetic compatibility'. (Prentice-Hall, 1990)
ELLIS, N.: 'Electrical interference technology'
(Woodhead Publishing)
GOEDBLOED, J.: 'Electromagnetic
ibility'. (Prentice Hall)
A text specifically concerned with explaining the
European Community EMC Directive is
compat-
MARSHMAN, C.: 'Guide to the EMC Directive
89/336/EEC' (EPA Press) 1992
JACKSON, G.A.: 'The EMC Directive
A third
status report'. Proceedings of EMC 92 conference.
ISBN 0 7008 0431 5
EMC in the 1990s is a rapidly developing field and
no one book can be said to adequately cover it.
Therefore a number of publications need to be
available to any reader who seeks either a broad
picture of the topic, or desires specific information
on a detailed aspect of it. I t is hoped that the
content and references given in this book enable
most readers to acquire the information on EMC
which they need.
An additional way of acquiring information and
learning new skills associated with EMC is via a
distance learning programme such as that offered
by the lEE. Brief details follow.
JACKSON, G.A.: 'The achievement of electromagnetic compatibility'. ISBN 0 7008 0400 5
'Safety and EMC' bimonthly newsletter.
Contact for all these: Publication Sales, ERA
Technology 0372 374151
OTT, H.W.: 'Noise reduction techniques in
electrical systems'. (Wiley Interscience, 2nd edn.)
'U nderstanding, simulating and fixing ESD
problems'. Don White Consultants ISBN 0-93
2263-27 -5
283
284
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
Electrom.agnetic com.patibility (with
particular em.phasis on EC Directive
89j336jEEC)
An lEE distance learning video course produced
by the York Electronics Centre, University of
York.
The course consists of 12 videos, in four modules,
total running time approximately 10 hours, with
accompanying course notes. I t is intended to be a
stand-alone training aid to be used either as an
individual teaching package, or with tutored
video instruction. The course identifies the range
of disciplines involved in achieving electromagnetic compatibility and provides a sound basis for
the application of design procedures to achieve
EMC and in particular to ensure conformity with
the EC Directive and the various CENELEC
standards currently applicable. It has a modular
structure to cater both for designers of electrical!
electronic systems and those involved in EMC
measuremen t and testing.
Module 1:
Video 1 EMC
explanatory introduction.
Covers the general nature of EMI,
definitions,
EMI
propagation
mechanisms, areas for concern e.g.
ignition hazards, overview of EMC
testing, design for EMC and future
trends Module 2:
Video 1 European Community Directive on EMC.
Describes EC Directive including scope,
essen tial
protection
req uiremen ts,
compliance, certification and marking
requirements, obligations of administra-
tion, legislation, flowchart of actions
required by manufacturers and suppliers
and relevant standards
Video 2 Relevant standards
Video 3 Achieving compliance
Module 3:
Video 1 Introduction to EMC measurements
RF measurement fundamentals
Video 2 EM waves
Radiation mechanisms
Measurements and measurement systems
Video 3 Screened rooms
Open-field test sites
Video 4 Practical measurements
Conducted emission measurements
Radiated emission measurements
Radiated immunity
Conducted immunity
Electrostatic discharge
Module 4:
Video 1 Shielding and crosstalk
Video 2 EMC on a PCB
Video 3 Conducted interference
techniques
Video 4 CAD for EMC
suppresslon
In addition, three videos on EMC are available as
part of the DTI awareness campaign available
from:
Technical Video Sales (New Electronics) 01322
222222.
The videos are
managers and
and 'Rou tes to
for these videos
book.
titled: 'EMC an introduction for
senior engineers', 'EMC design'
compliance (testing)'. The scripts
were written by the author of this
Index
rod 45
size field averaging 169, 21 7
spot size 81
TEM cell 45, 46, 48, 119, 123, 126
transmission line 48, 199
tuned dipole 45, 48, 89, 90, 91, III
wideband 96
Asymmetric TEM cell 126
Automatic EMC testing 151
emission testing 152
in the future 152
susceptibility testing 152
Absorbing current clamp 67,69
Accuracy in testing 42, 168, 214, 216, 21 7, 218
.Achieving product EMC 238
PC/IT example 238
Amplifiers, see Power amplifiers
Analysers, see Spectrum analysers
Anechoic screened chambers, see Screened rooms
ANSI 16,23,133,170,190,206,261,265,274
Antenna
aperture 74
balun 91, 170, 217
bandwidth 84
basics 72
beamwidth 79
biconic dipole 45, 48, 94, III
bounded wave 45, 119, 199
calibration uncertainty 21 7
'cavitenna' 158
conical logarithmic spiral 45,48,98, 113
Crawford cell 45, 48, 123
dipole, diode detection 48
dipole, electrically short 92
dipole, log-periodic 96
dipole, tuned half-wave III
effective length of 83
E field generator 115
electrically short dipole 48
74
factor, transmitting &
fibre, optically coupled 45, 48
for EMC 72, 73
110
for radiated susceptibility
free field 45, 48, Ill, 200
gain 73
GTEM cell 45, 48,110,126
horn 45, 48, 100
horn fed dish 48
input impedance 84, 169
log-periodic 45, 48, 96, 112
long wire 45, 48, 118
loop, active 106
loop, calibration of 106
loop, large 45
loop, passive 105
loop, small 45
magnetic field 105
monocone 48
monopole 45, 48, 86, 88
mutual impedance coupling 75
parallel plate line 45, 48, 119, 199
parallel plate line in screened room 122
phase centre 75
polarisation 83, 21 7
radhaz monitor 48
reflector 45, 103, 114
ridged horn 48, 102
Balanced hardening 233
Balun antenna, see Antenna, balun
Balun losses 170
Biconic dipoles 94, III
bow tie 94
commercial 94
use of 94
wire approximation 94
BPM (Deutsche Bundespost) 21
British Standards (EMC) 18, 133, 239, 254, 271
emission standards 18
for civil aircraft 18
immunity standards 18
BS727 33, 50, 93, 96
BS833 33, 254
BS905 coupling capacitor 58
BS905 LISN 50
British Standards (power disturbances)
BS2914206
BS5406206
BS6662206
British Standards (product safety) 264, 272
Broadband/narrowband signals 250
Bulk current injection (BCI) 171, 175
Capacitor
coupling RF 52, 56, 58
clamps 45, 59
distributed 45, 55, 59
feedthrough 44,48, 51, 55
for coupling to AC power circuits 54, 56
for coupling to I/O and control lines 55, 59
for use in BS6667 (IEC 801 pt 4) 53
for use in BS6667 (IEC 801 pt 5) 53,57
wideband 44
CENELEC EMC standards 18, 239, 254, 255, 256, 257
Circulator 151
CISPR £1\;11 meter detectors 21, 133
CISPR standards 16, 17,24,68,91,92, 133, 136, 154,
160,166,169,170,171,215,219,239,254
list of 258, 272
EMC standards 15,254
Civil and
285
286
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
Canadian E1\1 C
standards 25, 275
limits 263
comparing EMC tests 19, 260, 262
compendium of E1\'1 C and related standards 271
derivation of commercial standards 17
derivation of military standards 15
ESD and transient standards 27
European commercial standards 20, 254, 255, 256,
257, 273
examples of EMC standards 16
FCC requirements 23
generation of CENELEC E1\:1 C standards 18
German EMC standards 21, 259, 272, 273
Japanese EMC standards 24, 275
other US commercial standards (not FCC) 24
product-specific UK military standards 33, 34
range of standards in use 15
service specific standards (military) 31
UK/European commercial standards 18, 273
UK military standards 31, 268, 269, 270, 275
UK standards-commercial equipment 18,271
USA commercial standards 23,261,274
USA military standards 28, 275
USA military standards (other than 461/2/3 and
6051D) 31
Clamp-RF current 67,69
Coaxial couplers 150
Compatibility matrix 227
Competent body
list of 280
report from 246
Component burnout 196, 197, 232
Component upset levels 232
Cond ucted emission 48
Conduction and induction couplers 44, 48
Conformance test plan 40
Consultants (EMC) 223, 241
Consultants, list of 282
Control plan, see EMC control plan
Convolution 183
Couplers, coaxial, see Coaxial couplers
Couplers, directional, see Directional couplers
Couplers, distributed capacitance 55, 59
Couplers, inductive 61, 67, 69
CoupIers, waveguide, see waveguide couplers
Coupling capacitor, RF 52, 57, 58
Coupling, low-level swept, see Low-level swept coupling
Coupling models (simple) 229
Coupling, radiative 45
Coupling to victims 5
Crosstalk, capacitive and inductive 230
Current clamp 67, 69
Current probes
cable 44, 48, 61, 62, 172
injection 65
measurement method
principle of 62
surface 44, 48, 66, 68
transfer function 63
Definitions of EMC 1
DEF STAN 00-35 203
DEF STAN 05-74/1265
DEF STAN 59-41 7, 14, 33, 34, 49, 60, 64, 65, 154,
171, 175,265,277
list of tests 270
Design (for EMC) 223
approach to 242
for contractual assistance 224
for formal compliance 224
handbooks 225
hardening 235
process 225
example of 243
techniques 236
Detectors, see Receivers, EMI
Determining EMC requirement 241
DI-EMCS-8020 40
Diode detection dipole 48
J)ipole
aperture model (coupling to cables) 231
electrically short 92
log-periodic 96, 112
non-resonant 93
Roberts 92
tuned 89, III
tuned, commercial 91
tuned, practical 90
tuned, radiated emission testing 91
Direct connection devices 48
Directional couplers 148
Distributed capacitance couplers 55
DO 160 114,204
DTI 18, 218, 239, 252
EC 89/336 20, 41, 224, 246, 252
ECMA 190,240,273
ECSA 190
EEC 20, 21, 224, 246, 252, 253, 254, 259, 265, 273
EED 27
E-field generator 115
E-field levelling loop 117, 142
E-field sensors 48
EIA 23, 189, 241
EMAS 227
EMC
computer models 31
control plan 224
defini tions of 1
design, see Design for EM C
early problems 7
early problems with military equipment 9
hardening requirement 228
hardening techniques 235
historical background 7
information about 238
customer sources 238
industry sources 240
notified bodies 239
other sources 239
professional bodies 240
regulatory authorities 239
suppliers 240
legislation, see UK EMC legislation
philosophy of 12
INDEX
requirernent, see Determining EMC requirement
sensor groups 44
serious problems with 10
standards and specifications 14, 224
compendium of271
strategy 242
system specification 224
technical disciplines 10
test plan 227
training 241
sources of 282
useful publications 283
EMI
coupling to victims 5
receivers, intended and unintended 6
sources, broadcast 4, 5
sources, continuous 3
sources, intended 4
sources, man-made 3
sources, natural 3
sources of 1
sources, transient 3
sources, unintended 4
Emission suppression requirement 233
EN (European Norm) 19,21,41, 133, 136, 151,206,
218,239,254,255,256,257,273
Equipment case hardening requirement 233
ESD 27, 140, 179, 185,204
air discharge test 189
charged device model 187
con tact discharge test 189
direct injection 44, 48
event 185
field induced model 188
human body model 187
IEC80 1-2 new ESD test 190
indirect injection 45
latent defects 188
nurn ber of discharges required 191
probe 187
types of 187
types of test 188
vol tage test levels 191
waveform 186
EUROCARE lightning standard 204
European El\1C standards
existing and possible future 256
existing with eq uivalents 254, 255
proposed product specific 257
JTRC Uapan) 24
FAA 204
FCC (Federal Comrrlunications Commission) 16,18,21,
22,41, 136, 160, 169, 170, 171,215,218,261,
262, 274
FCC pt 15j 16,23,24,89,91,92, 154,239,254,260,
261,262,274
FCC requirements 23
Feedthrough capacitor 44, 48, 51
Ferrite-cored loop 48
Ferrite wand 48
Fibre-optic transmitter 173
Filters 136
Fourier transforms 180
Lightning 179, 201, 228
discharge, definition of 202
effects on equipment 204
aerospace equipment 204
ground equipment 204
environment 201
LISN 44,48
BS3G100 50
BS727 50, 52
BS905 50, 53
DEF STAN 59-41 51
developmen t of 49
direct injection 50
287
Frequency meters 142
FTZ (Central telecommunications office,
Germany) 18,22,218,260
German decrees and standards (EMC) 259
GS11 265
GTEM 45, 48, 110, 126
Hardening requirement, see EMC hardening
req uiremen t
Hardening techniques, see EM C hardening techniques
HERO 27
High-impedance voltage probes 56
HIRF 114, 154
Historical background 7
HPM 154
Hybrid ring 150
IEC 1, 14, 16,27,206,239,264,273,274
IEC 555 28
IEC 80127,53,55,57,59,110,114,119,121,187,188,
206, 224, 254
IEC 801-2 ESD test (new) 190
lEE 240, 241, 282
IEEE 16,23, 106,206,239,240,241,275
IEMCAP 31,226
Immunity first? 243
Impulse generators 137
Impulse response 182
Induction windings 45, 48, 70
Inductive clamp 45, 67, 69
Inductively coupled devices 61
Information about EMC, see EMC, information about
INIRC 27,265
Injection current probes 65, 175
Instrumentation
for emission testing 130
for susceptibility testing 142
Intersystem and intrasystem EMI 7, 223
Intrasystem EMC 223, 226, 227
Inverted 'V' coupling model 231
IPP-1 226
IRAC 23
ISM (industrial, scientific and medical) 16, 17, 24,
25, 274
ISO 218, 274
Isolator 151
288
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
for testing commercial equipment 50
5 microhenry type 49
50 microhenry type 49
specification of 49
Losses
in baluns 170, 217
in cables and connectors 170, 21 7
Low level swept coupling 172
Magnetic field probes 65
Magnetic field susceptibility tests 10
Magnetic induction tests 70, 107
Marconi 7
Mathematical modelling 11, 38, 39,44, 226, 227
Matrix, see Compatibility matrix
Measurement devices for conducted EMI 48
MIL-B-5087B 203
MIL-E-6051 D 31
MIL STD 461/2/3 7, 17,28,33,35,40,41,49,51,52,
56,60,64, 70,86,95, 105, 118, 119, 136, 154, 184,
206, 277
MIL STD 461B 30, 268
MIL STD 461C (NEMP) 31, 197
MIL STD 461 equipment classes 266
equipment and subsystem classes 268
test changes between 461 Band 461 C 268
test requirements applicable to classes 267
MIL STD 83141
MIL STD 1541 17,61
Modelling, see Mathematical modelling
Modulation rules 277
Modulators 147
arbitrary waveform generators 148
built in to equipment 147
req uiremen ts for 147
Monopole
active 88
passive 86
MVEE 33
NAMAS 21,209,210,215,217,218,219,240,245,
246, 247
accredited laboratories, list of 278
advantages of laboratory accreditation 220
document list 272
requirements for laboratory accreditation 219, 220
Narrowband/broadband signals 250
NASA 23, 157,203
NATO 212
NBS (NIST) 23,93, 163, 164, 167
NCMDRH 23, 265, 275
Near field/far field boundary 76, 217
NEC model 39, 227
NEMA 189
NEMP 110,154, 179, 184, 192,204,228
bounded wave simulator 199
exoatmospheric pulse 193
free field simulator 200
induced currents 194
testing 195
components 196
equipment 197
system 198
types 193
NES 1006 33
Notified bodies 239
NPL 93, 167,221
documents 272
NRPB 27,265
NTIA 23
NVLAP 23
NW0320 National Weights and Measures
Laboratory 19
NWS 3 33
NWS 1000 33
Open range test site 20,42,92, 165, 166, 167,246
Open range testing 165
site calibration 167
repeatability 168
antenna impedance changes with height 169
antenna size field averaging 169, 217
balun and VSWR losses 170,217
cable and connector losses 170, 217
differences in commercial antennas 170
EUT cables and peripherals 170
non-uniform field strength/range relationship 170
reflections from objects 168
weatherproof covers 168
testing proced ure 165
Ordnance Board 27
Oscilloscopes, digital 138
Parabolic reflector 114
Pick up on wires and cables 230, 231
Polarisation of antennas 83
Power amplifiers 144
frequency range 145
gain 145
gain compression 146
harmonic distortion 146
intermodulation distortion 146
output protection 147
power ou tpu t 145
specifying 145
TWT 147
Power disturbances 205
immunity standards 206
importance of transien ts 205
Power meter RF 141
Preselectors, see Spectrum analysers
Product
25, 26
radiation hazards 26, 27, 265
regulations typical 264
safety mark \lDE and TUV 26
of electrical devices 25, 264, 272, 274
Product specific UK military standards 33, 34
Prod uction
uncertain ty limits 219
Protection devices for amplifiers 148
Publications on EMC 283
Quasi peak detectors 20, 133
ANSI 20, 133
CISPR 20, 133
Radiated emission antennas 48
INDEX
Radiated imrnunity field strengths 114
req uiremen ts for civil aircraft 114
req uiremen ts for commercial products 114
requirements for military 115
Radiated susceptibility testing 110
antennas used 11 0
standards requiring 110
Radiation hazards 26
limits for exposure 27
Radiative coupling (EMC antennas) 45
RAM 34, 42, 161
Receivers, EMI 130
commercially available examples 134
design of 130
detectors 133
Al\l/FM 134
average 134
peak 133
quasipeak 20, 133
slideback peak 133
n1easuremen t uncertainty 21 7
selectivity and sensitivity 131
Regulatory authorities 18,22,218,239
Repeatability in testing 41, 168, 21 7
Routes to compliance 244
RRE 6405 33, 268, 269, 270
RSRE 33
RTCA 23,261
SAE 16,23, 190,203,204,239,241,261,274
Scope of EMC activity 7
Screened rooms/chambers 154
anechoic screened chambers 159
full RAM solutions 160
partial RAM solutions 159
attenuation of 155, 156, 157
elliptical chamber 160
enclosed chamber testing 154
mode-stirred 163
novel facilities 164
reflections in 158
standard shielded enclosures 155
tapered anechoic 162
Self certification 246
SEMCAP 226
Signal bandwidth 250
Signal modulators, see Modulators
Signal sources
tracking generators 143
sweepers 143
synthesisers 142
Spectrum analysers 134
operation 135
preselectors and filters 136
types 134
Spiral induction windings 45, 48, 70
Spot size, antenna 81
Staff support for EMC 235
Standards and specifications for EMC 14
civil and military 15
contents of 14
the need for 14
the need to meet 14
Strip lines, see Antenna, parallel plate line
Surface current probes 66, 68
Susceptibility hardening case study 231
System hardening (flow diagram) 233
System level requirements 228
System specification for EMC, see EMC system
specification
Technical construction file 244
circumstances requiring 245
contents of 245
or testing 246
'Technical disciplines in EMC 10
chemical knowledge 11
electrical engineering 10
legal aspects 11
mathematical modelling 11
physics 11
practical skills 12
quality assurance 12
systems engineering 11
Tempest 106, 154
Test differences between
FCC and VDE 260
FCC, VDE and VCCI 262
Test facility
cost of 248
in house 246
turnkey 248
Test plan, see EMC test plan
Testing 38
accuracy 42
automatic 151
conformance 39
conformance test plan 40
development 38
preconformance 39
regimes 154
repeatability 41, 217
to verify modelling 38
Time domain 181, 182, 183
Time domain manipulation 184
Training, see EMC training
Transformers
audio 45,60
directly connected 60
high-voltage 60, 61
injection 48
Transient injection 60, 62, 140
Transients power, see Power disturbances
Transient recorder, digital 140
Transient testing 179, 228, 246
transient types 179
Triboelectric series 186
Two box EMI problem 230
TUV safety mark 26
UK EMC legislation 252
UL (USA Underwriters Laboratories) 26, 264, 275
U ncertC\inty analysis 209 .
combining random and systematic
uncertainties 214
control factors 211, 216
289
290
A HANDBOOK FOR EMC TESTING AND MEASUREMENT
coupling factors 211, 216
definition of terms 209
estimates of for EMC 216
estimates of total uncertainty 218
in EMC measurement 214
measurement factors 210
standard deviation 212
student's 't' distribution 213
sys tematic uncertain ty 213
random variables 211
uncertainty 212
VCCI 24, 154, 171,239,262,275
VDE standards 17, 21, 24, 105, 106, 133, 215, 239, 259,
260, 262, 264, 272
Voltage probes 44, 48, 56, 61
Voltmeters AFjRF 141
VSWR 121,144,168,170,215,217
Wave impedance in TEM cell 124
Wavefield impedance 76
Waveguide coupler 149