Control System for Electromagnetic
Environmental Testing of Electronics with
Reverberation Chamber
Erik Olofsson, Jonny Jakobsson
February 13, 2010
Master’s Thesis in Physics, 30 credits
Supervisor at Combitech AB: Tony Nilsson, Mats Bäckström
Examiner: Bertil Sundqvist
Umeå University
Department of Physics
SE-901 87 UMEÅ
SWEDEN
Abstract
A reverberation chamber is a highly conductive cavity in which it is possible to generate
high electromagnetic fields that can be considered statistically homogeneous. Reverberation chambers have existed as a resource for electromagnetic compatibility (EMC) testing for
more than 30 years. Working to promote international co-operation on standardization, several organizations have published various EMC standards. At Combitech AB in Linköping
have a chamber that is commercially used for different types of measurements. To make
the chamber more attractive and versatile it is within their interest to get a system which
is compatible with the latest standards. The project aimed to develop a control system for
the reverberation chamber at Combitech and to equip it with functionality enabling it to
make measurements according to current EMC standards. Using the programming software
Agilent VEE a program was developed to communicate with the supporting equipment and
manage test routines. Within the program software lies functionality directly associate with
mode stirring and mode tuning procedures for standards DO-160F and MIL-STD. During
measurements the program has abilities for skipping frequencies, pause/continue the current
sweep, executing preset events and adding commented markers to the plot window. Some
other usable functionality implemented is project save/load, help section, directory selection
and data export abilities. The system holds functionality enabling measurements according
to the standards in question, though future work will be needed to be able to carry through
a proper and correct measurement routine.
ii
Acknowledgements
The thesis project is a mandatory and graduating part of the 4,5 year master programme
in Engineering Physics programme at Umeå University. The project extent is 20 weeks and
was carried out at Combiteh AB in Tannefors, Linköping, Sweden.
We would like to thank Combitech for giving us the opportunity to carry out this project.
Many thanks to everyone working at Combitech, for helping us and making the time there
very enjoyable.
We would especially like to direct a warm thank you to the following people: our supervisors
Tony Nilsson and Mats Bäckström for supporting the work during the project, Tomas Nilzon
for helping us in the laboratory and our examiner Bertil Sundqvist at Umeå University.
i
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Contents
1 Introduction
2 Problem Description
2.1 Problem Statement
2.2 Goals . . . . . . .
2.3 Purposes . . . . . .
2.4 Methods . . . . . .
2.5 Related Work . . .
2.6 Limitations . . . .
2.7 Restriction . . . .
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3 Theory
3.1 Electromagnetic compatibility . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2 Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2.1 Spectrum analyzer (spectral analyzer) . . . . . . . . . . . . . . . . .
3.2.2 Signal Generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2.3 Electronic Amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2.4 Receiving/Transmitting antennas . . . . . . . . . . . . . . . . . . . .
3.2.5 Field probe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2.6 Stirrer System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3 Reverberation chamber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.4 Field Statistics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.5 Antenna factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.6 Losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.7 E-Field in the Chamber . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.8 Requirements and test procedures . . . . . . . . . . . . . . . . . . . . . . .
3.8.1 RTCA/DO-160F Standard . . . . . . . . . . . . . . . . . . . . . . .
3.8.1.1 Radiated Susceptibility (RS) Test; Alternative Procedure Reverberation Chamber . . . . . . . . . . . . . . . . . . . .
3.8.1.1.1 Calibration (Mode Tuning) . . . . . . . . . . . . .
3.8.1.1.1.1
Procedure . . . . . . . . . . . . . . . . . . .
3.8.1.1.2 Chamber loading . . . . . . . . . . . . . . . . . . .
3.8.1.1.3 Test Procedure (Mode Tuning) . . . . . . . . . . .
3.8.1.2 Radiated Emissions (RE) Test; Alternative Procedure - Reverberation Chamber - mode stirring . . . . . . . . . . . .
3.8.1.2.1 General requirements . . . . . . . . . . . . . . . .
3.8.1.2.2 Insertion Loss . . . . . . . . . . . . . . . . . . . .
3.8.1.2.3 Radiated RF Emission test . . . . . . . . . . . . .
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iv
CONTENTS
3.8.1.2.4 Equipment categories for RF emission . . . . .
MIL-STD-461F Standard . . . . . . . . . . . . . . . . . . . . . .
3.8.2.1 Test Procedure - Reverberation chamber (mode-tuned)
3.8.2.2 Calibration . . . . . . . . . . . . . . . . . . . . . . . . .
3.8.2.3 EUT testing . . . . . . . . . . . . . . . . . . . . . . . .
3.8.2.4 Thresholds of susceptibility . . . . . . . . . . . . . . . .
3.8.2.5 Chamber time constant . . . . . . . . . . . . . . . . . .
Agilent VEE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.9.1 Developer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.9.2 Visual programming language (VPL) . . . . . . . . . . . . . . . .
3.9.3 Dataflow programming . . . . . . . . . . . . . . . . . . . . . . . .
3.9.4 Dataflow functionality in VEE . . . . . . . . . . . . . . . . . . .
3.9.5 Integrated Matlab Engine . . . . . . . . . . . . . . . . . . . . . .
3.9.6 .NET Framework Integration . . . . . . . . . . . . . . . . . . . .
3.9.6.1 Common language runtime (CLR) . . . . . . . . . . . .
3.9.6.2 .NET Framework class library . . . . . . . . . . . . . .
3.9.7 Capabilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.8.2
3.9
4 Results
4.1 Drivers . . . . . . . . . . . . . . . . . . . . . .
4.2 RC software . . . . . . . . . . . . . . . . . . .
4.2.1 Welcome screen . . . . . . . . . . . . .
4.2.2 Main window . . . . . . . . . . . . . .
4.2.3 File . . . . . . . . . . . . . . . . . . .
4.2.3.1 New project . . . . . . . . .
4.2.3.2 Open . . . . . . . . . . . . .
4.2.3.3 Save . . . . . . . . . . . . . .
4.2.3.4 Devices . . . . . . . . . . . .
4.2.3.4.1 RF Generator . . .
4.2.3.4.2 Spectrum Analyzer
4.2.3.4.3 Pre Selector . . . .
4.2.3.5 Sweep events . . . . . . . . .
4.2.3.6 Center marker . . . . . . . .
4.2.3.7 Sweep . . . . . . . . . . . . .
4.2.3.8 New Sweep . . . . . . . . . .
4.2.3.9 Power On/off . . . . . . . . .
4.2.3.10 Sweep Frequency list . . . .
4.2.3.11 Exit . . . . . . . . . . . . . .
4.2.4 Stirrer . . . . . . . . . . . . . . . . . .
4.2.4.1 Options . . . . . . . . . . . .
4.2.4.2 Reset Controller . . . . . . .
4.2.4.3 Run Setting . . . . . . . . .
4.2.4.4 Connect . . . . . . . . . . . .
4.2.4.5 Disconnect . . . . . . . . . .
4.2.4.6 Run Setting . . . . . . . . .
4.2.5 Frequency . . . . . . . . . . . . . . . .
4.2.5.1 Options . . . . . . . . . . . .
4.2.5.2 Frequency List . . . . . . . .
4.2.5.3 Skip Frequencies . . . . . . .
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CONTENTS
4.2.5.4 Go to Value . . . . . . . . .
Strength . . . . . . . . . . . . . . . . .
4.2.6.1 Options . . . . . . . . . . . .
4.2.6.2 Target . . . . . . . . . . . . .
4.2.6.3 Adjust strength . . . . . . .
4.2.6.4 Go to value . . . . . . . . . .
4.2.6.5 Step up . . . . . . . . . . . .
4.2.6.6 Step down . . . . . . . . . .
4.2.7 Calibration . . . . . . . . . . . . . . .
4.2.7.1 DO160-F/MIL/IEC . . . . .
4.2.8 Plot . . . . . . . . . . . . . . . . . . .
4.2.8.1 Export data . . . . . . . . .
4.2.8.2 Settings . . . . . . . . . . . .
4.2.8.3 Close All . . . . . . . . . . .
4.2.9 View . . . . . . . . . . . . . . . . . . .
4.2.9.1 Toolbar . . . . . . . . . . . .
4.2.9.2 Status Bar . . . . . . . . . .
4.2.10 Help . . . . . . . . . . . . . . . . . . .
4.2.10.1 Program content . . . . . . .
4.2.11 Equipment . . . . . . . . . . . . . . .
4.2.11.1 Instrument communication .
4.2.11.2 Stirrers communication . . .
4.2.12 Software to Controller communication
4.2.6
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5 Conclusions
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5.1 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
5.2 Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
References
75
A Tables
77
B Figures
81
C Work Distribution
85
C.1 Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
C.2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
Chapter 1
Introduction
Combitech AB is one of Sweden’s largest consultancies and is an independent company
within the Saab group. Combitech is combining technology with environment and security
awareness. The company has approximately 800 employees which operate in twenty cities
in Sweden, but also in Norway and Germany. Areas of work for Combitech are: Information security, System integration, Mechanics, Systems security, Systems development and
Logistics. The part of Combitech where we have done our project is located in Tannefors,
Linköping. This group is mainly targeted against electromagnetic compatibility (EMC).
The company says: ”Today is EMC a part of our everyday work”. This means that they are
working as a support to all parts in the chain that compound today’s project development:
from specification of requirements to verification and validation. Combitech aims to have
competence and facilities to meet today’s and future challenges on the EMC-area. They
offer services within counseling, analysis, testing, design support, education and simulations.
One of the resources at Combitech is a reverberation chamber. The chamber is a large
metal cavity which works almost as a microwave oven. It is used for testing different types
of electromagnetic compatibility. The main advantage with the cavity is that from a low
input power is it possible to get high field strength due to resonance of the electromagnetic
waves. Combitech is in need of a new control system for the chamber that fulfills both civil
and military standards. The aim of the project is to create a program software that controls
the stirrers in the chamber, the field generator and the measuring devices. The program
should be able to run a test sweep, collect information and present it, all with a user friendly
interface. Flexibility is important when instrument setup often changes.
The first part of the report is the problem description which states the problems that the
project will solve. It also covers goals, purpose and methods for the project. In the theory
chapter is an explanation of the concepts and theory behind a reverberation chamber and
how to perform a test. This chapter also covers the theory behind basic equipment when
conducting EMC tests. The result chapter explains how the developed program software
works, what it can do and how it communicates with stirrers and instruments. The last
part is the conclusion where the result is discussed and future work is suggested.
1
2
Chapter 1. Introduction
Chapter 2
Problem Description
2.1
Problem Statement
Reverberation chamber techniques came primarily as a result of poor repeatability and measurement accuracy in shielded-room EMC testing. With enhanced theoretical models the
reverberation chamber has, during the latest decade, become a useful tool supported by
several EMC standards. The current system for conducting tests with the reverberation
chamber at Combitech does not hold the possibility to make tests according to the newer
civil and military requirements. There are limitations within the current program software
and no newer commercial software options are available. There are also equipment compatibility limitations and the knowledge around the software structure is not entirely within
the company.
2.2
Goals
The project goal is to develop a new control system for the reverberation chamber at Combitech, with the intention to increase the number of different types of measurement procedures available for the chamber and thereby make it more attractive to customers. The
main goals of the project can further be listed as follows:
• Program software should be flexible and have a user-friendly and logical user interface.
• Working communication between program software and equipment/instruments.
• Working communication between program software and stirrer controller.
• Integrate two out of three standards into the program software.
2.3
Purposes
Procedures and theory regarding reverberation chambers are under constant discussion. The
content and procedures in the standards can therefore be expected to be updated in the near
future. If a total reformation of the system with external competence would be expensive
then the project is a good compromise to following the development of the standards but
minimizing the risk of ending up with an expensive system that could soon be out of date.
3
4
Chapter 2. Problem Description
The main purpose of the project is to update the old system and to create a new system
base consisting of solutions and procedures required by newer standard requirements for
EMC testing. The knowledge around the system is also intended to be integrated within
the department rendering the possibility of adding routines and updates to the system to
follow the future development of standards.
2.4
Methods
Within the project access is given to the entire test facility together with documentation
of standards. The main tool during the project is the new programming software Agilent
VEE used to set up overall control and link together communication of the system. The
old system used an ISA interface connection between the personal computer and the stirrer
controller. The new system should use a newer interface (LAN) and so the connection
and communication is to be rebuilt. Another communication interface introduced is GPIB
(general purpose interface bus), where connection should be established between the software
and supporting equipment and instrumentation. In Agilent VEE we will have to build
a whole new program with a user friendly GUI (Graphical user interface) and to equip
it with suitable procedures and logical functions. Influences to program layout, routines
and procedures are mainly found in older program software’s and documents describing
standards.
2.5
Related Work
As the reverberation chamber has been used with EMC applications for more than 30 years,
extensive theoretical research has been done on the subject during the years and you can
today find various reverberation chambers with different shapes for different applications.
The first standardized methodology using reverberation chamber was the MIL-STD (Military standard) 1377, which came in 1971 [1] and handled shielding effectiveness of cables
and enclosures. Up until today standards have arisen and been revised to follow the theoretical progress. When it comes to reverberation chamber measurement systems, they can
vary a lot in chamber form, equipment and program software. Influences for this project
will mainly be previous measurement systems and softwares for the reverberation chamber
at Combitech.
2.6
Limitations
An issue is the ability to maintain the chamber as a commercial resource while rebuilding the
system. During the development it should be easy to switch back and run tests according
to the old setup. The reverberation chamber and equipment will also be inaccessible for us
during time used by customers. Delivery time for the new controller will result in partial
code generation without being able to test its compatibility with the controller system.
The system is required to be flexible in the ability to change supporting equipment, which
restricted parts of the program software.
2.7. Restriction
2.7
5
Restriction
As the chamber at test generates dangerously high field strengths there are restrictions and
precautions needed when running tests and handling certain equipment.
6
Chapter 2. Problem Description
Chapter 3
Theory
This chapter covers the theory needed to understand electromagnetic compatibility (EMC)
testing. The basic concept of EMC is first presented. Then follows a description of the
equipment needed, theory on how the electric field is created, statistical properties in the
chamber and factors needed to adjust the measured field. The last part of the theory is a
summary of how to perform a test according to MIL and DO-160F standards.
3.1
Electromagnetic compatibility
The phenomenon that spark gaps generate electromagnetic waves rich in spectral content
which can cause interference or noise in various electric devices is commonly known. Electronic devices functioning with other electronic equipment in the surroundings without generating or being vulnerable to interference is considered to be electrically compatible with
the environment. The conditions for a system to be electromagnetically compatible are [2]:
1. It does not cause interference with other systems.
2. It is not susceptible to emissions from other systems.
3. It does not cause interference with itself.
Electromagnetic energy transfer can be further divided into several subgroups: radiated
emission, radiated susceptibility, conducted emission and conducted susceptibility. The importance of meeting the EMC requirements is not just satisfactory performance, but there
are also legal requirements to be able to distribute equipment commercially.
To limit the electromagnetic emission of electric systems there are standards published
in document form. The performance specifications in a standard are generally the minimum
requirements for an adequate function within the permitted design tolerances when working
in their proposed environment. In most countries there are national agencies suppressing
standards or regulations concerning electromagnetic emission, with the military being more
detailed and strict. In a growing fraction of European countries standards concerning electromagnetic emission and immunity to electromagnetic emission are compulsory even for
non-military applications for commercial use.
7
8
Chapter 3. Theory
3.2
Equipment
The equipment involved in basic EMC testing and calibration with a specified reverberation
chamber is:
1. Spectrum analyzer (spectral analyzer)
2. Field probe
3. Transmitting/Receiving antennas
4. Electronic amplifier
5. Stirrers
Here follows a short description of the individual equipment:
3.2.1
Spectrum analyzer (spectral analyzer)
A spectrum analyzer is mainly used to reproduce spectral composition or power spectrum
of some connected signal [3].
The analog spectrum analyzer can either use a variable band-pass filter which is automatically tuned over a range of frequencies that corresponds to the measurement spectrum.
A superheterodyne receiver can also be used. A local oscillator signal tuned over a range
of frequencies is then mixed with the input signal, to convert the processed signals to more
convenient frequencies.
A digital spectrum analyzer (FFT Analyzer) mathematically processes a sampled waveform into its frequency spectrum with a Discrete Fourier Transform (DFT). Some can even
mix the above described techniques; one example is the real-time spectrum analyzer. The
processed signal is first down-converted in frequency using heterodyning and then analyzed
with Fast Fourier Transformation (FFT) techniques.
3.2.2
Signal Generator
Signal generators produce repeating or non-repeating electronic waveform signals in either
digital or analog form [4]. Newer generators produce waveforms with digital signal processors and use a digital to analog converter (DAC) to create an analog output. Signal
generators have the ability to produce sine wave signals in the range from low frequency
up to many GHz. Typical features of a signal generator are attenuation, modulation and
sweeping.
3.2.3
Electronic Amplifier
The electric amplifier takes a signal from a power supply and generates a new high powered
signal together with waste heat by matching the output signal with the input signal [5].
Amplifier manufacturers always strive to reduce the resistance of the amplifying circuit
element. This increases efficiency and minimizes power waste, which allows transistors,
tubes or other amplifying parts to run cooler and hence be more reliable.
3.3. Reverberation chamber
3.2.4
9
Receiving/Transmitting antennas
Antennas are used for transmitting or receiving electromagnetic waves in the chamber.
The most important property for the receiving and transmitting antenna in a reverberation
chamber is the bandwidth. The bandwidth is the range of frequencies where the antenna can
radiate or receive energy properly. Other properties like directivity, gain and polarization
are lost in the chamber due to the resonance phenomena.
3.2.5
Field probe
A field probe consists of three independent broadband antennas oriented orthogonally which
each measures one component of the electric field. The signal from the probe is transmitted
digitally through a fiber optical link to a read out unit or computer. The RMS (root mean
square, effective value) value for the three components of the field represents the summed
total field [6].
Compared to antennas connected to a spectrum analyzer where the analyzer differentiates
between frequencies, the field probe responds to all active frequency components. Consequently a clean signal in an immunity testing setup is vital, particularly the harmonic field
generated by a power amplifier.
3.2.6
Stirrer System
The stirrers are large metallic reflectors whose main purpose is to change the boundary
condition inside the reverberation chamber. The design of the tuners can also alter the
lowest usable frequency for the chamber. During the rotation of the stirrers the standing
wave pattern in the chamber will be altered and every point in the working volume will be
subjected to the same maximum, minimum and average electromagnetic field. The chamber
fulfilling this condition is called well-stirred hence granting a statistically isotropic field for
EMC/EMI testing.
3.3
Reverberation chamber
A reverberations chamber (Figure 3.1) is a highly conductive cage, which is electrically
shielded from the outside. Highly conductive implies that the material of the chamber has
a low absorption of the field. Because of the shielded environment it is possible to get high
field strengths from a relative low input power. The electric field in the chamber is mixed
by stirrers to get a uniform field. A uniform field is reached when almost every point in the
chamber, over a complete rotation of the stirrer, is exposed to the highest field strength. An
isotropic field has the drawback that the information about polarizations and directional
properties is lost. Reverberation chambers are useful in electromagnetic compatibility tests
for several reasons. Some of the advantages are: it is easy to get strong fields from low
input power, good repeatability for several tests, cost effective test procedure and well
known statistics, which means that errors can be calculated. There are also drawbacks with
a reverberation chamber. One is that it is sometimes hard to relate the environment in the
chamber to the real world. Another one is that the lowest usable frequency (LUF) is relative
high, which can be a problem when the lower frequencies are important.
10
Chapter 3. Theory
Figure 3.1: A computer model of the reverberation chamber at Combitech AB
Reverberation chambers can differ in size. Smaller chambers have the advantage of higher
field strengths than the larger chambers, but the disadvantage of higher LUF. Larger chambers have lower LUF but also lower field strength compared to a small one. The LUF
depends on the chamber dimensions and its quality factor. To derive this relation it is
necessary to understand how the field is created in the chamber.
Constructive interference will occur for frequencies that match with chamber dimensions.
Resonance frequencies for a rectangular chamber can be derived by using solutions for the
corresponding waveguides given by Maxwell’s equations. The equation for the propagation
constant for TE (transverse electric) and TM (transverse magnetic) modes is
β 2nm = k 20 −
nπ 2
a
−
mπ 2
b
,
(3.1)
where n, m are constants and a and b are two dimensions of the chamber [7]. k 0 is the
angular wave number
k0 =
2πf
2π
=
,
λ
c
(3.2)
where λ is the wave length, c is the speed of light and f is frequency [8].
A resonance wave arises when the wavelength matches the length of the chamber. This is
when the length of the chamber is a multiple of half of the wavelength. From this comes a
requirement that the propagations constant has to be the ratio between a multiple of the
half wavelength and the length of the chamber in the propagation direction d as
β nm =
lπ
, l = 1, 2, 3...
d
(3.3)
3.3. Reverberation chamber
11
[7]. Solving for k 0 in equation 3.1 together with equation 3.3 to get the angular wave
numbers corresponding to the resonance frequencies gives
kmnl =
mπ 2
b
+
nπ 2
a
+
lπ
d
2
.
(3.4)
The resonance frequencies(fr ) are derived by using equation 3.2 together with 3.4 as
s
2
l
c m 2 n 2
+
+
(3.5)
fr = fmnl =
2
b
a
d
where m, n, l are constants, and at least two have to differ from zero. a, b, d are the chamber
dimensions.
The electromagnetic signal that is transmitted into the chamber can create a standing wave
pattern (a mode) if it is a resonance frequency or close to one. One mode can be considered
excited if the transmitted frequency is inside a 3 dB bandwidth from a resonance frequency.
This frequency area is given by the frequency band (∆f ) and depends on the quality factor
(Q) for the chamber as
fr
∆f =
(3.6)
Q
[9]. The quality factor Q is a measure of how well the walls reflect the signal power transmitted into the chamber. A large Q value gives a small band of frequencies that will be
excited but on the other hand a good reflection of the strength. A small Q value gives a wide
band of excited frequencies but less reflected field strength. The Q-value for a reverberation
chamber can be calculated as
16π 2 V Pr
Q=
(3.7)
λ3
Pt
.[9] The function of a reverberation chamber is dependent on the number of possible modes
that can be excited around the transmitted signal. The neighboring resonance frequencies
have to be close enough to each other for the modes to overlap (overmoded). When this
happens it is likely to get high and constant field strength inside the chamber. In the case of
low or no overlap (usually for lower frequencies and high Q value) there is a high probability
to get large differences in field strength between different points in the chamber. Frequencies close to a resonance frequency will cause large field strength while other frequencies will
produce an almost zero field strength.
The criterium for a sufficient amount of modes (N) is usually satisfied by saying that there
should be at least a certain number of modes up to the lowest usable frequency,
8πV
N=
3
3
f
f
1
− (a + b + d)
+
c
c
2
(3.8)
where V is the volume.[9]
The density of modes that is excited for a given frequency are obtained by taking the
derivative of equation 3.8 as
dN
8πV
1
8πV
= 3 f 2 − (a + b + d) ≈ 3 f 2 .
df
c
c
c
(3.9)
12
Chapter 3. Theory
Using df = ∆f from equation 3.6 gives the number of modes that are simultaneously excited
as
Ns =
3.4
8πV f 3
.
c3 Q
(3.10)
Field Statistics
When NS is considered large (overmoded) the chamber is very large compared to the wavelength and the number of modes is sufficient. When deriving statistical distributions for
the chamber NS → ∞ is assumed. As stirrers are introduced in the reverberation chamber
their movement alters the boundary conditions. The result is an electric field where the
amplitude in every given position is a sum of multipath plane waves with random phases.
A three dimensional electric field vector
E = Ex + Ey + Ez
(3.11)
consists of a real as well as an imaginary part according to
Ex,y,z = Re(Ex,y,z ) + iIm(Ex,y,z ).
(3.12)
Stirrer movements generate a large collection of waves in different directions. The real and
imaginary components of the wave can, according to the central limit theorem, be considered
normally distributed. Considering the chamber to be ideal and taking into account that the
real and imaginary parts of the rectangular components are non-correlated, the mean and
mean square fields has relations
hRe(Ex,y,z )i = hIm(Ex,y,z )i = 0
(3.13)
hRe(Ex,y,z )2 i = hIm(Ex,y,z )2 i ≡ σ 2 .
(3.14)
and
From statistical theory the variance of a random variable can be derived as
σ2 =
N
1 X
(xi − hxi)2
N i=1
(3.15)
[10]. Taking into consideration the relations in equations 3.13 and 3.14, the variance according to equation 3.15 becomes
σ2 =
N
1 X
E2
(Ei − 0)2 = 0 .
N i=1
6
(3.16)
E02 is the mean square of the electric field magnitude E. All six parameters are normally
distributed around a zero mean with a variance σ 2 , which consequently makes the square
of the magnitude of the field chi-square (χ2 ) distributed and the magnitude of the resultant
field chi (χ) distributed. Six random parameters lead to both distributions having six degrees of freedom.
3.4. Field Statistics
13
From statistical theory a χ2 distribution with n degrees of freedom can be derived as
fY (y; n) =
1
σ n 2n/2 Γ
1
2n
y (n/2)−1 e−y/2σ
2
(3.17)
[11], for y ≥ 0. Y have the relation Y = X 2 where X is a Gaussian random variable. Γ is
the Gamma f unction defined as Γ(n) = (n − 1)! if n is a positive integer. Hence with six
degrees of freedom the respective probability density function become
|E|2
|E|4
2
exp − 2
(3.18)
fY |E| =
16σ 6
2σ
and
|E|5
|E|2
fY (|E|) =
exp − 2
8σ 6
2σ
(3.19)
[12]. Measurements are commonly taken with a linearly polarized antenna which results
in one rectangular component and two parameters of the electric field. The χ distribution
will in this case hold two degrees of freedom and the probability density functions have
the characteristics of a Rayleigh distribution. The Rayleigh probability density function is
defined as
2
−x
x
(3.20)
f (x; σ) = 2 exp
σ
2σ 2
[13] for x ∈ [0, ∞), with cumulative distribution function
x2
F (x; σ) = 1 − exp − 2 .
2σ
(3.21)
Hence the density functions become
|Ex,y,z |2
|Ex,y,z |
exp −
f (|Ex,y,z |; σ) =
σ2
2σ 2
(3.22)
|Ex,y,z |2
F (|Ex,y,z |; σ) = 1 − exp −
2σ 2
(3.23)
and
respectively [12].
The chamber electric field uniformity is related to the discrete number of stirrer positions as
it generates new uncorrelated fields. An E-field measurement at a given position can ideally
be considered distributed according to statistical distributions either by stirrer movement or
by placing the measurement point at a new position. In a correctly working chamber environment where this condition is fulfilled the electric field is considered statistically isotropic.
A χ2 -hypothesis test is a relatively easy procedure that can be used to test probability models. This is often used to verify the chambers’ ability of demonstrating isotropic behavior
with a series of uncorrelated E-field measurements at a given position.
14
3.5
Chapter 3. Theory
Antenna factor
The Field strength inside a chamber is measured by an antenna and transmitted to a
measuring device. The value measured is the voltage over the antenna, but the value of
interest is the magnitude of the field per meter. Conversion between the measured field
strength and the field strength per meter can be done by using the antenna factor(AF ),
E
,
UA
AF =
(3.24)
where E is the total electric field in the chamber and UA is the average voltage over the
antenna.(Equations used to derive the antenna factor are only valid for the average electric
field in a reverberation chamber.)
The total electric field in the chamber is derived by using the receiving cross section for an
antenna as
λ2
Gr pq,
(3.25)
4π
where λ is the wavelength, Gr is the gain of the receiving antenna, p is the polarization
factor and q is the impedance mismatch factor [9].
σr =
The average power received (Pr ) by the antenna is given by multiplying the receiving cross
section(σr ) by the power density S of the chamber.
Pr = σ r S =
λ2
Gr pqS
4π
(3.26)
The power density is calculated by dividing the electric field with the impedance (Zc ) of the
chamber [14].
S=
E2
,
Zc
(3.27)
The average power received by the antenna is calculated by taking the average measured
voltage (U ) from the antenna and dividing that by the system impedance (Zs ) as
Pr =
U2
.
Zs
(3.28)
Equations 3.27 and 3.28 are substituted into equation 3.26 as
U2
λ2
E2
=
Gr pq
.
Zs
4π
Zc
Equation 3.29 may now be solved for
for the antenna factor as
E
U
(3.29)
and substituted into 3.24 to get a new expression
s
AF =
Zc 4π
.
Zs λ2 Gr pq
(3.30)
3.6. Losses
15
The wavelength can be rewritten as λ = fc .The impedance of the chamber Zf reespace can
be assumed to be the impedance for free space which is approximated by 120π. The polarization is assumed to be p = 21 for a reverberation chamber because it is either zero or one
with an average of 21 . There is no gain in an isotropic environment, so Gr is equal to one.
q is assumed to be one.
The final expression for the antenna factor in a reverberation chamber is an approximation for the maximum total field instead of the average total field and is
s
AFtotal =
960π 2 c
.
Zsystem f
(3.31)
It should be noted that this is not a good approximation, which is showed in [15].
The rectangular component of the maximum total field is given by taking AFrectangular =
√1 AFtotal (the square root is because it is an squared relationship between power and
3
electric field, P = E 2 ) as
AFrectangular
1
=√
3
s
960π 2 c
=
Zsystem f
s
320π 2 c
.
Zsystem f
(3.32)
It has been shown that the equation 3.32 is a good approximation for the rectangular component of the antenna factor for the maximum electric field [15].
The electric field in the chamber can now be calculated by taking the measured voltage
multiplied by the antenna factor as
Echamber = UA · AF.
3.6
(3.33)
Losses
The signal in the chamber is received by an antenna which has internal losses. The signal
is then transmitted from the chamber to a measuring device. This is done through cables
where the signal also loses strength. These losses have to be corrected for by multiplying
the E-field equation 3.33 by a loss term L as
Echamber = UA · AF · L.
3.7
(3.34)
E-Field in the Chamber
The E-field in the chamber is often presented in decibel instead of in voltage per meter. The
conversion of equation 3.34 is done as
Echamber,dB = 20 log (UA ) + 20 log (AF ) + 20 log (L) .
(3.35)
16
Chapter 3. Theory
3.8
Requirements and test procedures
This section covers an interpretation of the two standards RTCA/DO-160F and MIL-STD461F. It should be read as an overview of the standards where the focus has been on
procedure and instrument setup.
3.8.1
RTCA/DO-160F Standard
This standard is an updated version of the EMC requirements for commercial avionics that
are intended to reflect the “state of the art in aviation technology and EMC testing methodology” and could be related to every type of aircraft in use today. The update was made by
RTCA (Radio Technical Commission for Aeronautics) Special Committee 135 in an attempt
to meet FAA (Federal Aviation Administration) or other international regulations regarding equipment that is installed on commercial aircraft. During creation and modification
there was collaboration with the European Union version of RTCA, EUROCAE which has
released the standard under the name EUROCAE/ED-14F [16].
3.8.1.1
Radiated Susceptibility (RS) Test; Alternative Procedure - Reverberation Chamber
The test is intended for susceptibility measurements between 100 MHz to 18 GHz and aims
to simulate and qualify equipment for natural occurring RF-levels. In certain cases more
tests can still be appropriate.
The theory of chapter 3.8.1.1 is derived in more detail in the document by RTCA [17].
3.8.1.1.1
Calibration (Mode Tuning)
For the field to be considered uniform requirements for the number of discrete stirrer steps
has to be fulfilled. Verification must be done with an empty chamber after construction
or major modifications. The Lowest test frequency (fs ) is 100 MHz and field uniformity
should be verified over one operational decade from any chosen start frequency above fs .
It will be usable from the frequency where uniformity is first shown (LUF = Lowest usable
frequency). The test should be carried out at 9 test locations for all spatial axes (x, y and
z), so in total 27 measurements points are to be considered. Operation with continuous
tuning rotation (mode stirring) is not allowed.
3.8.1.1.1.1
Procedure
1. The working volume must first be cleared. (i.e. conductive test bench should be
removed)
2. The receiving antenna can be mounted at any location within the working volume,
see Figure B.1.
3. The amplitude measurement instrument is then to be set on monitoring the frequency
for the receiving antenna.
4. The optimum direction of the transmitting antenna is against one of the corners, as
it shall not directly illuminate the working volume. It should be fixed at the same
position during calibration and tests.
3.8. Requirements and test procedures
17
5. The E-field probe should be mounted on the border edge of the working volume according to Figure B.1
Note:
Surfaces of the working volume should not be distanced below 0.75 meter
(λ/4 of the lowest test frequency) from chamber surfaces, stirrer assembly
or field generating antenna. This distance is also the lower limit for distance
between probe and receiving antenna, i.e. every new measurement location
should at least have this distance to any previous location. It may be reduced provided that the separation distance is larger than λ/4 for the lowest
frequency, though below 1/4 meter is not recommended.
6. Starting at fs appropriate power (Pt ) from the RF-source should be passed to the
transmitting antenna. The RF-source must be in frequency band of transmitting- and
receiving antennas. The antennas should both be linearly polarized.
7. Stepping stirrer(s) 360◦ in discrete steps is recommended as the field uniformity can
hence be determined for fewer tuner steps. This enables altering the number of steps
for tests depending on if possible high field or fast test time is of importance. The
steps should still be sufficiently large to generate a new uncorrelated field at each step
and the number of positions should always secure the field uniformity requirements.
Sufficiently long dwell time is important so that measurement instruments and E-field
probe can respond correctly.
Quantities measured over one stirrer rotation is:
7.1 Maximum magnitude of received power Pr,M ax
7.2 Average magnitude of received power Pr,Rec (Watt)
7.3 Maximum field strength EM axx,y,z for every axis of the E-field probe (27 measurements below 10fs and 9 above 10fs ).
7.4 Total maximum field strength ET otal (root sum squared of the rectangular components).
7.5 Average transmitted power Pt,Ave (at least equal amount of samples as steps).
Note:
Calibrations are antenna specific and antenna efficiency (ratio of power accepted to the total power at the measurement location) is required.
8. Measurement procedures in step 7 should be done in log spaced frequency steps according to Table A.1. The steps can in ascending order be calculated as
fn+1 = fn ∗ 10(1/t) ,
(3.36)
where n is the current frequency, (n + 1) the next and t the number of frequency steps
per decade. The number of steps m required between the start frequency f1 and end
frequency fm can hence be calculated as
m = 1 + t ∗ log(fm /f1 ).
(3.37)
18
Chapter 3. Theory
9. The procedure should be repeated for nine probe- and antenna positions until 10fs .
Measurement positions should be spaced as in Figure B.1. Only three locations are
needed above 10fs , though one measurement position should always be in the center
of the working volume.
10. Measurement procedures in step 7 should then be carried out for the rest of the
calibration frequencies according to Table A.1.
Note:
Receiving antenna must be moved to a new location every time the probe is
moved. The antenna need also be rotated at least 20◦ around every chamber
axis (x, y, z) for each location.
11. With data from step 7 every maximal E-field measurement from the probe should be
normalized by taking the square root of the average transmitting power according to
M axx,y,z
bx,y,z = Ep
E
Pt,Ave
(3.38)
M axT otal
bT otal = Ep
E
.
Pt,Ave
(3.39)
and
EM axT otal is the total maximum of the total E-field from each probe measurement
location. (9 measurements under 10fs and 3 above).
Receiving antenna calibration factor ACF should also be calculated for all frequencies
as it is later used for comparison with a loaded chamber. It is calculated as the ratio
of average received power to input power as
*
+
Pt,Ave
ACF =
,
(3.40)
Pt,Ave
n
where n represents the number of measurement positions used at the current frequency
(9 under 10fs and 3 above).
Note:
Pt,Ave for equations 3.38 and 3.39 is calculated as the average transmitting power during the stirrer lap when respective maximum (EM axx,y,z and
EM axT otal ) was measured.
12. For every calibrated frequency under 10fs the average normalized maximum is calculated for every axis of the E-field as
bx i9 =
hE
X
bx /9
E
(3.41)
by i9 and hE
bz i9 .
and in the same way for hE
The average of the normalized maximum of all 27 E-field probe measurements is
calculated as
b 27 =
hEi
X
bx,y,z /27.
E
(3.42)
3.8. Requirements and test procedures
19
13. Step 12 should be repeated for every frequency over 10fs . Because of the three measurement positions 9 should be replaced with 3 and 27 with 9 in equations 3.41 and
3.42 respectively.
14. Confirming field uniformity is made by calculating the standard deviation from the
average value of the maximum values gathered at each measurement position during
one stirrer rotation. Only frequencies below 10fs are to be considered.
14.1 Standard deviation is calculated as
v
2
uP u
bi − hEi
b
E
t
,
σ =α∗
n−1
(3.43)
bi is a specific measurement of the
where n is the number of measurements, E
E-field and α is 1.06 for n ≤ 1 and 1 for n ≥ 20. Expressed in dB the standard
deviation corresponds to
#
b
σ + hEi
.
σ(dB) = 20 ∗ log
b
hEi
"
(3.44)
14.2 To establish field uniformity the standard deviation of the field components
(σx,y,z ) must not exceed the standard deviation specified in figure B.2 for more
than two frequencies per octave (within 3dB over 400 MHz and fall linearly from
6 to 3 dB from 100 MHz to 400 MHz). The standard deviation for all vector components (σ27 ) must also not exceed specified standard deviation. If the chamber
doesn’t fulfill the terms it can’t be used at lower frequencies, though with a low
margin it may be possible to get uniformity by
• Increasing the number of stirrer steps by 10 - 50 %
• Normalizing data against the chamber net input power (Pnet = Pt,Ave −
Pref lected )
• Reducing the size of the working volume.
With a confirmed uniformity condition the number of stirrer steps can be reduced,
but not below 12 steps.
Note:
After modifications of the chamber setup (for instance added absorbent)
or calibration, it is important that configuration/procedure stays the same
during following tests for the calibration to be considered valid.
3.8.1.1.2
Chamber loading
This procedure should be run prior to test to check if the EUT has loaded the chamber.
The EUT should not occupy more than 8 % of the chamber volume. The number of stirrer
steps should be equal to the number chosen for the later equipment test procedure but
the frequency range with logarithmic steps should be the same as for the calibration. The
chamber calibration factor CCF is the normalized average received power over one stirrer
20
Chapter 3. Theory
rotation and with EUT and other equipment present. It should be calculated at every
frequency as
+
*
Pr,Ave
,
(3.45)
CCF =
Pt,Ave
n,f
where n is the number of antenna locations (only one is needed) and f the number of
frequencies the value is averaged over. The chamber loading CLF factor is then calculated
as
CCF
CLF =
,
(3.46)
ACF
and when calculated for a given frequency the ACF and CLF data sets can be averaged
over up to 4 of the closest frequency values on both sides. If the magnitude of the chamber
loading factor becomes too large the uniformity check has to be done again with an object
loading the chamber equally as the current EUT.
3.8.1.1.3
Test Procedure (Mode Tuning)
1. The transmitted power for every test frequency should be decided from the electric
field intensity category level in Table A.1 and equations
#2
"
ET est
(3.47)
Pt =
√
bT otal i ∗ CLF
hE
n
and
Pt =
ET2 est
.
|ET |2max ∗ CLF
(3.48)
The categories determine the radio frequency test levels and may be prescribed by
the equipment performance standard. The choice of equation to be used depends
on whether a measurement probe or a receiving antenna is used as calibration data
bT otal in
receiver. In equation 3.47 ET est is the demanded field strength (V/m) and hE
the average of the normalized maximal E-field. Interpolation between the calibration
b for the
frequency points will be needed to get the normalized E-field calibration (E)
test frequencies.
In equation 3.48 |ET |2max is the squared maximum magnitude of the E-field defined as
*
+
PAveRec
8πη
2
|ET |max =
∗ 2 ∗ R,
(3.49)
Pt ∗ ηrx
λ
where R is the maximum to average ratio of the square magnitude of the E-field
tabulated in table A.2. ηrx is the antenna efficiency factor which can be presumed to
be 0.75 for a log periodic antenna and 0.9 for a horn antenna. η is the wave impedance
of free space (120π) and λ the wave length (m).
2. The number of stirrer steps used for the test has to be considered, the minimum
number of steps, still with a uniform field, will result in the highest input power but
shortest test time.
3. Field strength is derived from Pt in step 3.47 and verification is made by noting the
value from the receiving antenna.
3.8. Requirements and test procedures
21
4. The Frequency interval should be stepped through until the upper limit with appropriate modulation, the carrier modulated according to field level categories as:
• Category R→From 100-400 MHz: 20 V/m CW and 20 V/m with 1 kHz square
wave modulation (at least 90 % depth).
From 400 to 8 GHz: 150 V/m pulse modulated (4% duty cycle) and 1 kHz pulse
repetition frequency. At 1Hz rate and 50% duty cycle switch off and on signal to
simulate the effect of rotational radars.
• Category S, T, W and Y→ CW from 100 MHz to the upper frequency (S = 2
GHz, T = 8 GHz, W and Y = 18 GHz) and 1kHz square modulation (at least 90
% depth). Additional modulations associated with the EUT can be considered.
• Category B, D, F, G and L→ From 100 MHz to 18 GHz when testing suiting
SW/CW with accordance to table A.1: CW and 1 kHz square modulation (at
least 90 % depth). Additional modulations associated with the EUT can be considered.
From 400 MHz - 4 GHz: Pulse modulated (PM) test level with at least 4 µs pulse
width and 1 kHz pulse repetition frequency.
From 4 GHz - 18 GHz: Pulse modulated (PM) test level with at least 1 µs pulse
width and 1 kHz pulse repetition frequency. For EUT with low frequency response consider switching the signal off and on at a 1 Hz rate and 50 % duty
cycle
• All categories → Above 1 GHz: Allowed to use SW modulation at 1.42*CW field
strength requirement to meet CW and SW requirements at the same time.
Dwell time has to be at least one second excluding equipment settling time. Additional
dwell time may as well be needed for ”off time” at low frequency modulation and for
the EUT to do internal operations.
5. While dwelling apply necessary measurements and evaluate functionality for EUT
under applicable performance standards.
3.8.1.2
Radiated Emissions (RE) Test; Alternative Procedure - Reverberation
Chamber - mode stirring
Radiated emission tests are done to ensure that the EUT doesn´t emit undesired RF noise
to the surrounding. Different equipment categories (see 3.8.1.2.4) have different limits (see
appendix B) for RF noise. The chamber must meet the field uniformity requirements of
section 3.8.1.1.1 at or above 100MHz.
The theory of chapter 3.8.1.2 is derived in more detail in the document by RTCA [18].
3.8.1.2.1
General requirements
Important parts of the general requirements:
1. The peak detector time constant must be lower than or equal to 1/bandwidth. Video
bandwidths should be equal to or greater than the resolution bandwidths.
2. For detecting time-varying emissions the dwell, sweep and measurement times may be
chosen to a longer time than specified in Table A.4.
22
Chapter 3. Theory
3. Recorded data should provide a minimum frequency resolution of 1% or twice the
measurement receiver bandwidth and minimum amplitude resolution of 1 dB.
3.8.1.2.2
Insertion Loss
It is necessary to make a measurement of the insertion loss before a radiated emission test.
This measures how much of the input power that is lost from the transmit antenna to the
receiving antenna due to chamber properties and loading of the chamber. This measurement
is done with the EUT in the chamber together with all support equipment. The EUT and
other equipment should be turned off. The measurement of the insertions loss follows the
procedure below.
1. The spectrum analyzer should be in peak detector mode and the display set for peak
hold
2. The RF generator should be set to sweep a range of frequencies given in Table A.4.
The chosen minimum time for sweeping the frequency band should be divided by 100
to get the spectrum analyzer sweep time. The Spectrum analyzer should use a 1 MHz
IF BW. Time for one tuner rotation is calculated by multiplying the signal generator
sweep speed by 100. Signal generator sweep speed is calculated by dividing minimum
sweep time for the frequency band by the frequency range.
3. The RF source should transmit a known input power (Pt ) into the transmit antenna
and record it in dBm.
4. The tuner should be rotated one revolution so that the measurement receiver captures
the maximum power for every frequency.
5. The measurement receiver should save the maximum power measured (Pr ) for every
frequency.
6. Insertion loss (IL) for the reverberation chamber is calculated by
IL = (Pt − Lloss + (10log(η)) − Pr )
(3.50)
where Lloss =Transmit antenna line loss in dB, η=Transmit antenna efficiency. The
antenna efficiency can be assumed to be 0.75 for a log periodic antenna and 0.9 for a
horn antenna.
3.8.1.2.3
Radiated RF Emission test
Total RF emission is calculated by adding insertion loss from calibration to the measured
RF emission power. During the test the EUT and support equipment shall be powered and
had time to stabilize. Before starting, the EUT should be tested for normal operation.
1. Operating mode of the EUT should be chosen to be the one that produce maximum
emission.
2. The transmitting antenna should be terminated outside the chamber with a 50 ohm
load.
3. The measurement receiver should monitor the receiving antenna at the bandwidth
specified in Table A.4.
3.8. Requirements and test procedures
23
4. The measurement receiver should be in peak detection mode and the display on peak
hold.
5. The sweep time for the measurement receiver should be set to the value specified in
Table A.3 for the minimum sweep time of the frequency band. Sweep time of the
measurement receiver should be multiplied by 200 to obtain the time for one tuner
rotation.
6. The stirrer should be rotated one full rotation so that the measurement receiver captures the peak power from the receiving antenna across the chosen range of frequencies.
7. EUT RF emission power should be calculated by using
Pt =
10(Pr +IL)/10
,
1000
(3.51)
where Pr =max power in dBm from the receiving antenna, IL=insertion loss in dB.
8. Electric field strength E should be calculated by using
r
DPt 377
,
E=
4π
(3.52)
where E is the field strength in volts per meter, D=1.64, which is the directivity of
the EUT and is assumed to be equivalent to that of a half wave dipole antenna.
9. Electric field emissions (dbuV/m) should be calculated as
dBuV /m = (20log(E)) + 120
(3.53)
where E=field strength in volts per meter.
10. The emission measured should then be checked by applying the appropriate limit from
figures: B.3, B.4,B.5 and B.6 for the different categories 3.8.1.2.4.
11. the ambient radiated RF (EUT ”off”’ and test support equipment ”on”) should then
be measured to check if emissions are higher than the selected category 3.8.1.2.4 limit
minus 3 dB. It is desirable that the ambient emissions should be at least 6 dB below
the selected category limit.
3.8.1.2.4
Equipment categories for RF emission
1. Category B:
For equipment where interference should be controlled to tolerable levels.
2. Category L:
For equipments that is located far from apertures and a radio receiver´s antenna.
Suitable for equipment and associated interconnecting wiring located in the electronic
bay of an aircraft.
3. Category M:
For equipments and interconnected wiring located in any areas where apertures are
electro-magnetically significant and not directly in view of radio receiver´s antenna.
Suitable for equipment and associated interconnecting wiring located in the passenger
cabin or in the cockpit of a transport aircraft.
24
Chapter 3. Theory
4. Category H:
For equipment that is located in areas which are in direct view of a radio receiver´s
antenna. Applicable for equipments outside the aircraft.
5. Category P:
For equipments and associated wiring located in areas close to high frequency, VHF, or
GPS radio receiver antennas, or where the aircraft structure provides little shielding.
3.8.2
MIL-STD-461F Standard
Military standards MIL-STD-461 and MIL-STD-462 make a multifaceted collection of standards in electromagnetic compatibility which was first introduced in 1967-68. MIL-STD-461
refers to EMI/EMC stipulations for electrical, electronic, and electromechanical equipment
and subsystems [19]. MIL-STD-462 handles test process and detailed events to meet the
terms for MIL-STD-461. Both documents have during the years been revised from D up
till today’s F version. The standard is mainly used by the U.S. Department of Defense, but
many other countries follow it closely or with slight variation. The EMI control levels within
the standard should ensure electromagnetic compatibility for extensive hardware integration
between subsystems. Within the standard, tolerable levels concerning conducted emission,
susceptibility and immunity to conducted emissions, radiated emission, and susceptibility
and immunity to radiated emission are presented.
3.8.2.1
Test Procedure - Reverberation chamber (mode-tuned)
This procedure is suitable to use for the frequency range from around 200MHz to 40GHz.
MIL-STD-461F has the recommendation that if number of possible modes is less than 100
for a given frequency, the chamber shouldn’t be used at or below that frequency. See equation 3.8 for how to calculate number of possible modes [20].
The MIL standard specifies the maximum scan rate and the maximum step size for different
frequency ranges which are shown in Table A.4. Both scan rates and step sizes are defined
from f0 which is the start frequency for a sweep. It also specifies the number of stirrer
positions for different frequency ranges, as seen in Table A.5. A lower frequency gives a
higher number of stirrer positions, and a higher frequency gives a lower number of positions.
This is because there have to be enough modes in the chamber to ensure that every point
in the chamber has the highest field value for some stirrer position.
3.8.2.2
Calibration
Calibration of the chamber is done to determine how much RF power that is needed to create
desired field strength inside the chamber. There is two types of calibration depending on
whatever a receiving antenna or an electric field probe is used.
• Receiving antenna procedure
1. An appropriate unmodulated input power (Pt ) should be transmitted into the
chamber at the start frequency.
2. The stirrers should be rotated one revolution with a minimum number of steps
given in Table A.5. The stirrer should dwell at each step longer than 1.5 times
the response time for the measurement receiver. At each step should the field
3.8. Requirements and test procedures
25
strength be measured and the highest recorded field strength should be saved,
Pr,max .
3. The calibration factor (V/m) is then calculated from the transmitted power and
the recorded maximum field as
r
Pr,max
Er,max
8π
5
Calibrationf actor = √
=
.
(3.54)
λ
Pt
Pt
4. This should be repeated for frequency steps of maximum 2% of the preceding
frequency until 1.1 times the start frequency is reached. After that, the steps
should be a maximum of 10% of the preceding frequency.
• Electric field probe procedure
1. An appropriate unmodulated input power (Pt ) should be transmitted into the
chamber at the start frequency.
2. The stirrers should be rotated one revolution with a minimum number of steps
given in Table A.5. The stirrer should dwell at each step longer than 1.5 times the
response time for the measurement receiver. At each step should each element of
the probe be measured and the highest recorded field strength should be saved
Ex,y,z,max .
3. The calibration factor (V/m) is then calculated from the transmitted power and
the recorded maximum field as
v
u
u Ex,max +Ey,max +Ez,max 2
t
3
Calibrationf actor =
.
(3.55)
Pt
4. This should be repeated for frequency steps of maximum 2% of the preceding
frequency until 1.1 times the start frequency is reached. After that, the steps
should be a maximum of 10% of the preceding frequency.
3.8.2.3
EUT testing
The same antennas as used during the calibration should be used during EUT testing.
1. Measurement equipment should be turned on and allowed to stabilize.
2. The RF source should use a 1 kHz pulse modulation with a 50% duty cycle and be
set to the start frequency.
3. Calculate the amount of RF power (Pt ) needed to create the desired field strength (Er )
by using the calibration factor from the calibration. Interpolation between calibration
points is required.
2
Er
Pt =
(3.56)
Calibrationf actor
It should be verified that the desired field is present
4. The stirrers should be rotated one revolution with a minimum number of steps given
in Table A.5. The stirrer should dwell at each step by the time specified in Table A.4.
As the stirrers rotate, the transmitted power should be maintained to produce the
desired field levels.
26
Chapter 3. Theory
5. The required frequency range should be swept as specified in 4 for each frequency.
Monitor the EUT performance for susceptibility effects.
6. If susceptibility is noted, the threshold level should be determined by the procedure
in section 3.8.2.4 to verify that it is above the limit.
3.8.2.4
Thresholds of susceptibility
If susceptibility is noted, the threshold level should be determined. This level is when the
susceptible condition is no longer present. The threshold is determined by the following
procedure,
1. If a susceptibility condition is noted then the transmitted power should be reduced
until the EUT recovers.
2. The transmitted power should then be reduced another 6 dB.
3. Increase the transmitted power until the susceptibility condition is noted again. That
level is then the threshold of susceptibility.
4. Record threshold power level, frequency range swept, frequency and level of greatest
susceptibility and other test parameters.
3.8.2.5
Chamber time constant
The chamber time constant is a constant determining how long time it takes to build up a
field in the chamber. This is important when using pulsed waveform testing. If the time
constant is too large relative to the pulse, then it can be difficult to reach the desired field
strength. In order to assure that the chamber is fast enough the following procedure could
be used.
1. Calculate the chamber Q using
Q=
16π 2 V
ηT x ηRx λ3
Paverage
Pinjected
(3.57)
where ηT x and ηRx are the antenna efficiency factors for the transmit and receive
antennas, respectively, and can be assumed to be 0.75 for a log periodic antenna and
0.9 for a horn antenna, V is the chamber volume (m3 ), λ is the free space wavelength
(m) at the specific frequency, Paverage is the average received power over one tuner
rotation, and Pf orward is the forward power input to the chamber over the tuner
rotation at which Paverage was measured.
2. By using the Q-factor in equation 3.57 is the time constant, τ is calculated as
τ=
Q
.
2πf
(3.58)
3. The chamber constant is not allowed to be greater than 0.4 of the pulse width. In case
of greater value is it necessary to add absorber material into the chamber or increase
the pulse width.
3.9. Agilent VEE
3.9
3.9.1
27
Agilent VEE
Developer
Agilent VEE is a development environment created by Agilent Technologies based on a
visual and data flow programming language. VEE is the short form for what was originally
called Visual Engineering Environment, but now days it is officially named just ”VEE”.
3.9.2
Visual programming language (VPL)
The main feature of a visual programming language is that programs are created by manipulating program elements graphically rather than specifying them textually. A VPL
utilizes programming with visual expressions and spatial arrangements of text-graphic symbols, representing elements of syntax or secondary notation. Within the frame of the visual
programming environment the user is able to structure the iconic elements according to
some specific structure for program construction. Interpretation of element structure then
defines the data distribution of the program. Commonly boxes or other objects represent
entities with the connecting relations represented by arrows, lines or arcs.
Visual expressions for naturally visual languages are inherent with no textual equivalence,
where as a non-visual language having a superimposed visual representation is called visually transformed.
Classification of the programming language can be broken down further, according to the
type and extent of visual expression used, into icon-based languages, form-based languages
and diagram languages.
The principles of visual programming under chapter 3.9.2 is more extensively explained
at the internet reference [21].
3.9.3
Dataflow programming
The majority of programming languages are imperative, meaning that the program is executed as a sequence of instructions and the system is constantly in a certain ”state”. A
state can be seen as the measure of various conditions in the system and execution of each
instruction can modify it.
The lack of visualization of the states in imperative programming is a problem as the information needs to be shared across multiple processors in parallel processing machines.
Data flow programming implements data flow principles and architecture between operations and were introduced to simplify parallel programming and to structure languages
better suitable for numeric processing.
The logical execution flow of data is represented by nodes on a block diagram that are
connected to one another. These nodes can be reconnected in any way to or from different
applications without the need for internal change. The execution order of utilities on the
block diagram depends on the movement of data through the nodes which changes emphasis
from sequences of instructions to conversions performed on streams of data.
28
Chapter 3. Theory
Operations run when all inputs are valid and will be ”ready” at the same time without
tracking of hidden states, so the language is logically parallel. The asynchronous process
makes the time for events hard to predict, but as it turns out this isn’t necessary.
As data flow programming is highly visual and resembles more a real life processes, and it
is often used in hard real time problems. It can be pictured as a factory, where items travel
from station to station, undergoing various changes. Still it can be hard to work with flow
based programming without having an instantaneous map of the project.
The principles of dataflow programming under chapter 3.9.3 is more extensively explained
in the document by Paul J. Morrison [22].
3.9.4
Dataflow functionality in VEE
Programs in Agilent VEE are built by connecting objects that represent different data
sources. The data flows sequentially into an object from the left, gets treated and then the
resulting data flows out of the right side terminal. The sequence of execution is of the form
left to right, top to bottom and objects will execute when all input terminals have received
new data.
The ability to control the sequence of execution is possible because the objects have a
sequence input terminal on the top and a sequence exit terminal at the bottom. By wiring
the input sequence terminal on a specific object the user can “hold off” execution as it will
not execute until the object with the corresponding wire connected to its sequence output
terminal is executed. In this case despite having data on all data inputs the object will wait
for the sequence input terminal to be pinged. When data leaves the data output terminals
the object actively monitors the downstream objects, and not until they have all been executed it will execute its own sequence output (bottom) terminal. A typical object structure
in VEE can be seen in Figure 3.2.
3.9.5
Integrated Matlab Engine
R
R
VEE has an integrated MATLAB
(MathWorks
) engine with built in functions including
analysis and visualization functions from the MathWorks Signal Processing Toolbox [23].
With the object based MATLAB Script the user can reach roughly 1800 common MATLAB
functions.
3.9.6
.NET Framework Integration
VEE supports .NET automation and Windows Forms controls which can be run on any
Microsoft Windows operating system.
The framework is designed to fulfill the following objectives [24]:
• To provide a consistent object-oriented programming environment whether object code
is stored and executed locally, executed locally but Internet-distributed, or executed
remotely.
• To provide a code-execution environment that minimizes software deployment and
versioning conflicts.
3.9. Agilent VEE
29
Figure 3.2: Typical sequential data flow between objects in VEE.
• To provide a code-execution environment that promotes safe execution of code, including code created by an unknown or semi-trusted third party.
• To provide a code-execution environment that eliminates the performance problems
of scripted or interpreted environments.
• To make the developer experience consistent across widely varying types of applications, such as Windows-based applications and Web-based applications.
• To build all communication on industry standards to ensure that code based on the
.NET Framework can integrate with any other code.
The Common Language Infrastructure (CLI) is an open specification by Microsoft that
describes the executable code and runtime environment that form the core of the Microsoft
.NET Framework. A visual description of the CLI structure can be seen in Figure 3.3.
Two foundations of the Framework are the common language runtime and the .NET Framework class library.
3.9.6.1
Common language runtime (CLR)
The CLR generally works as an application virtual machine that manages code at execution
providing services as remote-controlling, memory- and thread management, compilation and
safety verification. Auto immunization of layout, reference handling and releasing objects
solves frequent errors of memory leaks and invalid memory referencing.
Enforcing strict code accuracy verification with a system called common type system (CTS)
and exception handling contributes to security and forcefulness. Depending on the parts of
30
Chapter 3. Theory
Figure 3.3: Visual description of the CLI structure [25].
a section it is given a degree of trust limiting the ability of operations. Code access security
is also inflicted by the runtime.
Users are able to take full advantage of the runtime, the class library and components from
other languages, and still be programming in their own language. Any compiler vendor
integrating the runtime offers all existing code access to the .NET Framework simplifying
migration for applications.
Including managed and unmanaged code gives a possibility to make use of COM elements
and DLLs. An attribute called just-in-time enhances performance while executing by running managed code in the native machine language. During this process fragmented memory and memory locality-of-reference is also managed to enhance performance even further.
Figure 3.4 illustrates how the common language runtime and the class library relates to an
application and to the overall system.
R
Microsoft
SQL ServerTM and Internet Information Services (IIS) can host the runtime.
3.9.6.2
.NET Framework class library
The class library is an object oriented set of reusable types from which the user can manage
code to develop functionality. Third party mechanisms can flawlessly be integrated with
3.9. Agilent VEE
31
Figure 3.4: Relationship of the common language runtime and the class library to an application
and to the overall system. The illustration also shows how managed code operates within a larger
architecture [24].
the .NET Framework with a possibility to develop collection classes with a set of interfaces.
The class library is versatile with programming features such as string management, data
collection, database connectivity and file access. Development of the subsequent applications
and services are also possible:
• Console applications.
• Windows GUI applications (Windows Forms).
• Windows Presentation Foundation (WPF) applications.
• ASP.NET applications.
• Web services.
• Windows services.
Programs based on the .NET Framework can be run in software environments that host the
program’s runtime.
3.9.7
Capabilities
The ability to control a large amount of instrumentation together with high level programming constructs in VEE is a strength. For example file I/O is managed with task oriented
To/From objects and memory allocation is controlled by the program.
Other capabilities are [26]:
32
Chapter 3. Theory
• Instrument Connectivity via:
◦ VXI plug & play drivers
◦ IVI - COM drives
◦ NI - DAQMX
◦ SCPI via the DirectIO object
• Built-in math and statistics including FFT and windowing functions
• Visual displays such Strip chart, Waveform, Polar & Smith charts
• Wide array of input controls for building operator user interfaces
• ActiveX Automation
• ActiveX Controls
• Socket IO via the To/From Socket object
Chapter 4
Results
The result of the project is a new control system for the reverberation chamber at Combitech
and is named RC. The program is designed to be able to fulfill the different requirements
from both civil and military standards. The program uses driver files for all communication
with the stirrers and instruments. This is done to fulfill the need of a program that operates
in a changing environment where instruments often change. The system is created with
Agilent VEE 9.0 as the platform, but interfaces are done with the help of .NET Framework
and some calculations uses the Matlab engine.
The basic flow of the program is divided into three blocks which are drivers, RC and equipments, as seen in Figure 4.1
Figure 4.1: Basic flow of the program divided into three blocks which is drivers, RC and equipments.
4.1
Drivers
The driver files are written as regular text files which are read by the program. These
files contain everything needed to use the program or to do a test. A driver file is used
by the program to: save and load program parameters, set instruments, communicate with
instruments and stirrers, read help files. There is a different formatting of the text files
depending on what they are used for.
• Drivers for menu options: Menu options are read into records when starting the
program. This record collects the different parameters for a menu into one group,
for example FrequencySaveOptions.MindB where FrequencySaveOptions is the record
and MindB is the parameter. Every option uses two lines in the driver file, the first is
the parameter and the second is the value for that parameter.
33
34
Chapter 4. Results
• Drivers for instrument communication: The communication driver for the respective instrument contains all GPIB commands that the instrument can send. The
file is divided into groups for different instrument actions. An action to pre-set the
RF generator could look like this in the driver file:
[P reSetRf Generator]
∗ RST
DISPLAY:STATE ON
:OUTput OFF
:POWer ]StrengthO ptionsS trengthSaveOptions.M indB]
[/P reSetRf Generator]
[text] is the group name for the sequence of commands needed to pre-set the RF
generator. This is the start line for the action when the program reads the driver file.
If a text is surrounded by ]text] it is read by the program as a global variable. If the
text between ]] contains a dot ”.” the variable is interpreted as a record. Every action
needs to end with the line [/text].
• Drivers for instruments: Instrument drivers contain a list of instruments that the
user can choose between in the program.
• Drivers for strength adjustment: These files contain two columns, the first one
contains x-values[Hz] and the second one is strength[dBm]. The two columns need to
be separated by a tab.
• Drivers for stirrers: Code representing controller routines and controller setup
commands are loaded from text files on to the controller. Among them the setup
files are static in the way that the code never changes between the times it is loaded
to the controller. However, when the user changes stirrer parameters like acceleration
and velocity in the program, the code for the stirrer movement must be changed. The
solution was to use the .NET functionality ”Stream writer” in Agilent VEE to export
text into text files. As the user saves settings the stirrer parameters are set by global
variables representing the user specified value as the whole code is streamed out to
the text file. An object in VEE that streams controller program code to a text file
when being executed can be seen in Figure 4.2.
4.1. Drivers
35
Figure 4.2: Object in VEE that when being executed streams controller program code to a text
file.
The file is then instantly loaded to the controller memory replacing the old program.
The files used are:
◦ OneMaster: This is one of the setup files that are loaded to set up the controller
with one ”master” in control of both stirrers. This setup is used for all settings
except when a time based move in mode tuning is considered.
◦ TwoMaster: This setup file is loaded to the controller to set the controller to
have one ”master” controlling each stirrer. This is only necessary in mode tuning
and using time based movement.
◦ Setup: Setup is the file loaded when resetting the controller and resets the basic
setting for the controller.
◦ Prog0: This is the file holding the current program to run settings except when
a time based move in mode tuning is considered.
◦ Prog1: This file is loaded to the controller when using time based move in mode
tuning. We then need two programs using each to control one master and hence
one stirrer.
◦ Defines: The file holds the controller internally defined variables.
• Drivers for help files: Except for plain text the help files can have tab items,
captions, and headings. For example, when writing the heading in a help file the user
starts the line with the heading text with the command ”heading”. In the same way
for a tab item or a caption the user writes ”tab” or ”caption” for the respective format
on the following text. When the user presses a help button or enters the ”Program
Content” menu in the program, help files will be presented to the user in a text box
object with the correct formatting. Figure 4.3 shows the text of a driver help file.
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Chapter 4. Results
Figure 4.3: Text file with commands and the corresponding text which is loaded when displaying
stirrer help text in the program.
Other formats can easily be added to the program if desired by the user.
4.2
RC software
RC is divided into several menu categories where the user has the ability to save data, load
data, change parameters or interface appearance and perform tests. The structure of the
program is complex and hard to show with a flow diagram. A simplified diagram of the
program structure is shown in Figure 4.4
Figure 4.4: A simplified diagram of the program structure.
4.2. RC software
4.2.1
37
Welcome screen
This menu works as the welcome screen (Figure 4.5). The user has here the possibility to
type in the name, choose a standard to follow and a test to do. Choices made in this menu
affect the options available in the program.
Figure 4.5: Welcome screen in RC.
• Standard: This is where the user can chose between the standards MIL and DO-160F.
If none is selected, then all functionality in the program is available
• Measurement: This is where the user can choose between the measurements radiated
susceptibility and radiated emission. If none is selected, then all functionality in the
program is available
The user can use the ”Quit” button to exit the program. If there are any concerns about the
parameters the ”Help” button is supposed to give information regarding this. The ”OK”
button takes the user to the main page of the program.
4.2.2
Main window
The architecture of the main window (Figure 4.6) is intended to have a commercial layout
and a logical structure with easy overview of chamber outputs.
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Chapter 4. Results
Figure 4.6: Main window in RC.
At the top are the different menus with submenus for configuration and communication with
the program. Under the menu is a control bar with buttons giving easy access to important
features. The different plot windows can be hidden and shown through the buttons on the
control bar. The control bar at the bottom gives information about chamber outputs when
performing a sweep.
The ”Main” tab of the control bar is divided into the sections: Stirrers, Frequency, Markers
and Actions.
Within the ”Stirrers” section the user receives instantaneous data output regarding stirrer
movement during a sweep. There are also three buttons for fast interactions. Within the
frequency section the user receives instantaneous data output regarding frequency stepping
and time consumption.
Within the ”Markers” menu there is one button to generate a marker note within the
strength plot window and one button to clear all marker notes generated during the current
sweep. When running a sweep a constant marker can be scrolled along all strength measurements in the plot window. When pressing the ”Set Marker” button a dialog window
pops up for the user to enter a message. When the message is entered data from that point
will be saved together with the message. Visually an ”X” marks the point where the marker
note was placed.
Then there is an ”Action” section with buttons enabling the user to stop, break or continue
a sweep. For example, the user can stop a sweep and save it as well as load a sweep and
continue it.
There is also an ”Additional” tab on the control bar that is indented to hold outputs and
4.2. RC software
39
interactive features of less importance. Right now buttons enable stepping with the marker
in the strength plot window, but if expanding the program leaves possibilities to implement
more options.
In the bottom of the main window is status strip giving information about time and date,
user, standard, type of measurement and data at the current marker position.
Figure 4.7: Setting a marker and making comments regarding q specific measurement value.
4.2.3
File
The file menu holds general functionality controls for the program. The user can start a
new, or open and old project, and save projects. Other submenus like devices, sweep events
and start sweeps are also found here.
Figure 4.8: The file menu and its selectable submenues.
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4.2.3.1
Chapter 4. Results
New project
The program basically restarts as settings are reset and the welcome menu is displayed.
4.2.3.2
Open
The open function lets the user load projects through a file browser. The executable file
is in the form of a text file. If the project was saved during a sweep the program will
automatically set up equipment and take all necessary actions enabling a continuing sweep.
If the load is aborted the user is alerted with a ”Nothing loaded” message.
4.2.3.3
Save
The user can at any time decide to save the current project, even in the middle of a sweep.
The user is asked where to save the project and the name of the project run file. If the folder
doesn’t exist the program will also ask if that folder is to be created. In the designated folder
together with the project file the program will make a folder containing text files holding all
information about program setup and data at the time the project was saved. If the save is
aborted the user is alerted with a ”Nothing saved” message.
4.2.3.4
Devices
In the devices menu there are options for the different instruments shown. The user here
has the ability to change parameters that specify how to communicate with the instrument.
The menu is divided into three tabs which are the different types of instrument available to
the user; these are a RF Generator, Spectrum analyzer and a Pre Selector.
4.2.3.4.1
RF Generator
Figure 4.9 shows the RF Generator tab. This is where the user can change the name, GPIB
address and file address from where the RF generator GPIB commands are read.
4.2. RC software
41
Figure 4.9: RF Generator tab in the device menu is where the RF Generator can be configured.
• Instrument Name: This list specifies the different RF Generators that are available
to the program.
• GPIB Address: Sets the GPIB address which will be used by the program to communicate with the instrument.
• Instrument driver: Specifies which driver file that will be used by the program.
This file contains the GPIB commands for doing actions with the RF generator.
• Text box: The contents of the chosen driver file will be presented in this text box.
If nothing is to be changed, the ”Exit” button can always be used to close the menu. If there
is any concerns about the parameters the ”Help” button is supposed to give information
regarding this. If any parameter is changed the ”Save and exit” button should be used when
exiting the menu.
4.2.3.4.2
Spectrum Analyzer
Figure 4.10 shows the spectrum analyzer tab, where the user can change the name, GPIB
address and file address from where the Spectrum analyzer GPIB commands are read.
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Chapter 4. Results
Figure 4.10: The spectrum analyzer tab in the device menu is where the Spectrum analyzer can
be configured.
• Instrument Name: This list specifies the different Spectrum Analyzers that are
available to the program.
• GPIB Address: Sets the GPIB address which will be used by the program to communicate with the instrument.
• Instrument driver: Specifies which driver file that will be used by the program.
This file contains the GPIB commands for doing actions with the spectrum analyzer.
• Text box: The contents of the chosen driver file will be presented in this text box.
If nothing is to be changed, the ”Exit” button can always be used to close the menu. If there
is any concerns about the parameters the ”Help” button is supposed to give information
regarding this. If any parameter is changed the ”Save and exit” button should be used when
exiting the menu.
4.2.3.4.3
Pre Selector
Figure 4.11 shows the pre selector tab, where the user can change the name, GPIB address
and file address from where the Pre Selector GPIB commands are read.
4.2. RC software
43
Figure 4.11: The pre Selector tab in the device menu is where the Spectrum analyzer can be
configured.
• Instrument Name: This list specifies the different Pre Selectors that are available
to the program.
• GPIB Address: Sets the GPIB address which will be used by the program to communicate with the instrument.
• Instrument driver: Specifies which driver file that will be used by the program.
This file contains the GPIB commands for doing actions with the pre selector.
• Text box: The contents of the chosen driver file will be presented in this text box.
If nothing is to be changed, the ”Exit” button can always be used to close the menu. If there
is any concerns about the parameters the ”Help” button is supposed to give information
regarding this. If any parameter is changed the ”Save Settings” button should be used when
exiting the menu.
4.2.3.5
Sweep events
In the sweep events (Figure 4.12) menu the user can specify events that will happen during
a test. Events can either be a GPIB or a message event. A message event will cause the
program to pause at the chosen frequency and show a message defined by the user. The
program continues as before the pause when pressing OK on the message. A GPIB event
will cause the program to send a GPIB command to the instrument address, both specified
by the user. The chosen event will happen before the specified frequency.
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Chapter 4. Results
Figure 4.12: The sweep events menu is where different events can be specified.
• Frequency column This column contains the different frequencies specified at which
the event will happen.
• Message/GPIB This column specifies the type of event. This is done by writing
either Message or GPIB in the field.
• Address This column sets the address to the instrument that will receive the GPIB
command. If ”message” is chosen in the column before then this is irrelevant.
• Message This is where the user can write the message/GPIB command to send either
to the screen or to the instrument.
The ”Add row” button adds a row to the list and the ”remove row” button removes one row.
If nothing is to be changed, the ”Exit” button can always be used to close the menu. If there
is any concerns about the parameters the ”Help” button is supposed to give information
regarding this. If any field in the list is changed the ”Set list” button should be used when
exiting the menu.
4.2.3.6
Center marker
This menu centers the marker in the strength plot.
4.2.3.7
Sweep
Procedures for both mode tuning and mode stirring are available within the program though
they should be seen as tests of the functionalities of the system as they do not fulfill standard
requirements yet. The program flow for the mode tuning procedure can be seen in figure
4.13.
4.2. RC software
45
Figure 4.13: Program flow for a mode tuning sweep.
First the RF-generator and the spectrum analyzer are preset to initiate measurements according to user specified settings. The field strength is then tuned with the RF-generator
to match the user specified initial value and the frequency is set to its initial value. The
frequency is then updated, i.e. increased or decreased. However, the first time the frequency
stays constant as the first strength measurement is taken at the initial frequency. As the
user has the possibility to arrange the program to skip frequencies a check is then made
if the frequency should be skipped, if this is the case the program loops back to yet again
update the frequency.
Another feature implemented is an event handler where the intention is to have a list of
actions that are executed at certain frequencies. This is checked immediately after the frequency update. Actions are in the form of changing settings for instruments, pause the
sweep and giving messages to the user.
The strength level is then checked to be within preset limits at the current frequency. It is
possible to set up advanced limit conditions within the frequency interval. If not within the
limits the strength is adjusted until within the given limits.
Then the stirrer procedure is started and the program loaded to the controller initiated.
First the stirrer(s) are stepped to the first position. As the stirrer(s) come to a halt the
program dwells for a given time and then reads the current field strength. Then the procedure starts over again until the stirrer(s) have made one full rotation and with strength
measurements corresponding to the number of discrete steps of the stirrer(s). Then the
highest strength is saved as it is the only one interesting for further evaluations.
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Chapter 4. Results
Finally the GUI is updated so that the user can follow the proceedings of the sweep with
comprehensible data.
If the current frequency is not the final frequency initially set by the user the program will
loop back to update the frequency and eventually retrieve a maximal strength value for that
frequency.
Figure 4.14: The main window and the field strength plot during a mode tuning sweep.
4.2. RC software
47
Figure 4.15: The main window and the power output plot during a mode tuning sweep.
The program flow for the stirring procedure can be seen in figure 4.16
Figure 4.16: Program flow for a mode stirring sweep.
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Chapter 4. Results
This procedure is very similar to the tuning procedure but with some small modifications.
When stirring the paddles should be in constant motion and so this is the first thing that
is initiated. All checks and updates then follow the tuning procedure until the strength
measurement. The strength is measured just once at each frequency while paddles are in
constant movement. Finally, like in the tuning procedure, the GUI is updated and the
program loops back to the frequency update state.
Figure 4.17: The main window and the field strength plot during a mode stirring sweep.
4.2. RC software
49
Figure 4.18: The main window and the power output plot during a mode stirring sweep.
4.2.3.8
New Sweep
This submenu resets any earlier sweep by clearing values and vectors needed to start a new
sweep.
4.2.3.9
Power On/off
This functionality lets the user control the frequency and the field strength in the chamber
by moving the marker. The marker position in x-direction sets the frequency for the RF
Generator and the position in y-direction sets the target level for the field strength in the
chamber. The user can at any time set the power off or on. Stirring is the only available
option for this function. The procedure when starting the ”power on” submenu is that:
First the RF-generator and spectrum analyzer are preset to initiate measurements according
to user specified settings. The field strength is then tuned with the RF-generator to match
the limits specified by the user, around the initial marker position(y-direction) and the
frequency is set to the initial position of the marker(x-direction).
The program will then loop a sequence where it sets the frequency and tunes the field
strength dependent of the marker position. This is done until submenu ”Power off” is
pressed which ends the RF generator transmission into the chamber.
4.2.3.10
Sweep Frequency list
The sweep frequency list is a functionality which lets the user sweep a specific list of frequencies. The list is set in submenu ”frequency list”(See section 4.2.5.2) under ”frequency”. The
program flow for this function is almost the same as the program flow for tuning/stirring in
a sweep (See figure 4.2.3.7). The only difference is that the dashed box (skip frequency) is
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Chapter 4. Results
erased. Skip frequency (See 4.2.5.3) is unnecessary when every frequency swept is specified
by the user.
4.2.3.11
Exit
This menu will exit the RC program.
4.2.4
Stirrer
The stirrer menu (Figure 4.19) consists of five submenus that all have to do with communication or settings for stirrer movement.
Figure 4.19: The stirrers menu and its selectable events and submenus.
4.2.4.1
Options
Under this menu settings for stirrer movement can be set. Figure 4.20 shows the opened
menu in the program software. Values are pre set with regards to the type of standard
chosen at start up. When a project is loaded the values under stirrer options will change
accordingly with the values at when the project was saved. Below follows explanations of
each parameter:
4.2. RC software
51
Figure 4.20: The stirrers options menu.
• Mode: Selection of run mode of paddles. Eligible modes are tuning or stirring.
• Acc: Acceleration for the paddle(s) during stepping and jogging. Unit is degrees/s2 .
• Dwell Time: Time of paddles’ stand still before measurement(s). The unit is seconds.
• Steps/Rev: Number of discrete measurement steps per revolution of paddle(s).
• Revolutions: Number of revolutions per measurement frequency.
• Velocity: Paddle(s) target velocity during stepping and jogging. Unit is degrees/s.
• Dec: Deceleration for the paddle(s) during stepping and jogging. Unit is degrees/s2 .
• Step Time: Time for each paddle step when time based move is active. Can only
be active in tuning mode. Limiting values for velocity and acceleration restrict the
possible input. The unit is seconds.
• Time Based Move: Activate time based move. Can only be set in tuning mode.
• Main Paddle Active: Enable main paddle stepping and jogging.
• Second Paddle Active: Enable second paddle stepping and jogging.
• Percent of Main: If both paddles are enabled, this value represents the reduction in
speed for the second paddle as a percentage.
If nothing is to be changed you can always exit the menu by using the ”Exit” button. If
there are any concerns about the parameters the ”Help” button is supposed to give information regarding this.
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Chapter 4. Results
If any parameter is changed the ”Save Settings” button should be used when exiting the
menu. As this button is pressed the program will flash the controller memory with a new
program in accordance with the parameter values set. As this is done a progress bar will be
displayed on the screen indicating the amount of data transferred (Figure 4.21).
Figure 4.21: The main window when flashing program code to the controller.
4.2.4.2
Reset Controller
The basic setup of the controller is specific for the application and can be flashed to the
controller memory like any other program. This option is implemented with the intention
that the controller could be used in other applications which hence need a different setup.
When switching from another application the user will have to run ”Reset Controller” to
reset and set up the controller correctly.
4.2.4.3
Run Setting
This option is implemented with the intention that the user wishes to control the stirrers
with the program developed but take measurements with other software. This is currently
mainly of interest when running mode stirring tests. When ”Run Settings” is executed the
current program flashed on to the controller is executed.
4.2.4.4
Connect
Before being able to communicate with the controller, the user will have to actively connect
to it. This is mainly because it contributes to a higher stability and a larger program access
without controller connection. When the controller is connected a ”Connected” message
is displayed on the screen (Figure 4.22). If any routine demanding the controller to be
connected is executed with a non connected controller, the user should be alerted about this
through warning messages.
4.2. RC software
53
Figure 4.22: The main window when successfully connected to the controller.
4.2.4.5
Disconnect
The program is always started with the controller disconnected, though when connected
the user always has the option of disconnecting the controller. When the controller is
disconnected the user is alerted with a ”Disconnected” message displayed on the screen
(Figure 4.23).
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Chapter 4. Results
Figure 4.23: The main window when successfully disconnected from the controller.
4.2.4.6
Run Setting
This option is implemented with the intention that the user wishes to control the stirrers
with the program developed but take measurements with other software. This is currently
mainly of interest when running mode stirring tests. When ”Run Settings” is executed the
current program flashed on to the controller is executed.
4.2.5
Frequency
The frequency menu is divided into six submenus. The first three are where the user can
adjust parameters that have effect on the frequencies in the chamber. The last three controls
the marker(x-direction) in the strength plot. Figure 4.24 shows the frequency menu.
Figure 4.24: The frequency menu and its selectable events and submenus.
4.2.5.1
Options
The frequency options (Figure 4.25) are parameters such as stop and start frequency, step
size, sweep direction and scale set.
4.2. RC software
55
Figure 4.25: The frequency options menu is where parameters connected to the frequency can be
changed.
• Min Frequency: Sets the minimum frequency for a sweep. This is the start frequency
in normal direction and the stop frequency for inverse direction of a sweep. The unit
is [Hz].
• Max Frequency: Sets the Maximum frequency for a sweep. This is the end frequency
in the normal direction and the start frequency for the inverse direction of a sweep.
The unit is [Hz].
• Scale Frequency: Scales the frequency axis (x) on the strength plot in either linear
or logarithmic[%].
• Step size: Sets the type of frequency step for a sweep. Choose linear for taking
the same length over the whole sweep. The unit is [Hz]. Choose logarithmic for
taking logarithmic steps during the sweep, this means that the next step length is a
percentage of the current frequency.
• Inverse Frequency: The default setting is to sweep from min to max frequency. If
this box is checked the sweep goes from max to min.
If nothing is to be changed, the ”Exit” button can always be used to close the menu. If there
are any concerns about the parameters the ”Help” button is supposed to give information
regarding this. If any parameter is changed the ”Save and exit” button should be used when
exiting the menu.
4.2.5.2
Frequency List
In the frequency list (Figure 4.26) menu the user has the ability to create a list of specific
frequencies that are desirable to test. These frequencies are swept from the sub menu ”sweep
frequency list” under the ”file” menu.
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Chapter 4. Results
Figure 4.26: The frequency list menu is where a list of specific frequencies to sweep can be specified.
• List of frequencies: This is where a list of frequencies to sweep can be specified.
The unit is [Hz].
”Add row” button adds a row to the list and the ”remove row” button removes one row. If
nothing is to be changed, the ”Exit” button can always be used to close the menu. If there
are any concerns about the parameters the ”Help” button is supposed to give information
regarding this. If any field in the list is changed the ”Set list” button should be used when
exiting the menu.
4.2.5.3
Skip Frequencies
In skip frequencies (Figure 4.27) menu the user has the ability to specify a list of frequency
intervals that the program will skip during the sweep.
4.2. RC software
57
Figure 4.27: The skip frequencies menu.
• From: This list specifies the start frequencies of the intervals that will be skipped
during a sweep. The unit is [Hz].
• To: This list specifies the end frequencies of the intervals that will be skipped during
a sweep. The unit is [Hz].
”Add row” button adds a row to the list and the ”remove row” button removes one row. If
nothing is to be changed, the ”Exit” button can always be used to close the menu. If there
are any concerns about the parameters the ”Help” button is supposed to give information
regarding this. If any field in the list is changed the ”Set list” button should be used when
exiting the menu.
4.2.5.4
Go to Value
The go to value menu is for moving the marker to a specific value on the frequency axis (x).
Figure 4.28 shows the menu.
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Chapter 4. Results
Figure 4.28: The frequency go to value menu is used for moving the marker to a specific value on
the x-axis.
• Step up: Moves the marker by one step up with the amount specified in frequency
options. See section 4.2.5.1
• Step down: Moves the marker by one step down with the amount specified in frequency options. See section 4.2.5.1
4.2.6
Strength
The strength menu (Figure 4.29) is divided into six submenus. The three first is where the
user can adjust parameters that affect the strength in the chamber. The last three controls
the marker (y-position) in the strength plot window.
Figure 4.29: The strength menu and its selectable submenus.
4.2.6.1
Options
Strength options are divided into two different tabs, strength and power. In the strength
tab, options for controlling the field strength limits and appearance of the strength plot can
be found.
4.2. RC software
59
Figure 4.30: The strength options menu is where parameters connected to the field strength and
power can be changed.
• Min Strength: This is the minimum strength that is shown in the strength plot.
• Max Strength: This is the maximum strength that is shown in the strength plot.
• Tolerance max: Max tolerance level by which the electric field strength can exceed
the target value. The target vector is set in menu 4.2.6.2.
• Tolerance min: Minimum tolerance level by which the electric field strength can be
below the target value. The target vector is set under menu 4.2.6.2.
• Strength scale: Scales the Strength axis (y) in the strength plot as, either linear or
logarithmic.
• Step size: Type of step to take when power is on. Linear is chosen for taking a specific
step length each step. Logarithmic is chosen for taking logarithmic steps during the
sweep. This means that the next step length is a percentage of the current strength.
The unit is [dBm].
In the power tab, options for controlling the input power to the chamber from the RF
generator are found. Figure 4.31 shows the power option tab.
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Chapter 4. Results
Figure 4.31: The power options menu and the strength tab.
• Min power: This sets the minimum power for the RF Generator. It is also the initial
power from which the Generator starts when starting a sweep. The unit is [dBm].
• Max power: This sets the maximum power that the RF Generator is allowed to give.
The unit is [dBm].
• Max Step: This is the maximum step that the RF generator is allowed to take. The
unit is [dBm].
• Step size: This is the step size for the RF generator when adjustment of the strength
is done. The unit is [dBm].
If nothing is to be changed, the ”Exit” button can always be used to close the menu. If
there is any concern about the parameters the ”Help” button is supposed to give information
regarding this. If any parameter is changed the ”Save and exit” button should be used when
exiting the menu.
4.2.6.2
Target
In the target menu (Figure 4.32)the user has the ability to create a target vector that the
program will aim for during a test. How close to the target line the strength needs to be is
set in strength options (Section 4.2.6.1) by the min/max tolerance level. The target vector
is created through points that are specified in this menu and then interpolated to a vector.
4.2. RC software
61
Figure 4.32: The strength target vector menu.
• Frequency: List of points on the frequency axis. The unit is [Hz].
• Strength: List of points on the strength axis. The unit is [dBm].
The ”Add row” button adds a row to the list and the ”remove row” button removes one
row. If nothing is to be changed, the ”Exit” button can always be used to close the menu. If
there is any concern about the parameters the ”Help” button is supposed to give information
regarding this. If any field in the list is changed the ”Set list” button should be used when
exiting the menu.
4.2.6.3
Adjust strength
It is necessary to adjust the strength measured by the antenna from voltage to field strength
by using the antenna factor. Other adjustments necessary could be losses in the antenna,
cables and other losses. This menu lets the user choose up to four files which contain values
to adjust the field strength. Figure 4.33 shows the adjustment menu.
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Chapter 4. Results
Figure 4.33: The adjust strength options menu is where the user can add files to adjust the field
strength.
Every file has two columns which contain frequency(x) and strength(y) values. The loaded
values are plotted in the adjustment plot (Figure 4.34). Regression between the points is
then done during the sweep to find out what value to add to the measured strength.
Figure 4.34: The main window with the adjust strength plot shown.
4.2. RC software
63
• Antenna factor: A correction needed is to convert the measured voltage to voltage
per meter. This is done by adding a file with antenna factor adjustment values. See
Chapter 3.5 for antenna factor theory.
• Cable loss: Transmitting the power received by the antenna to the measure device
is done through cables where the signal loses strength. This is adjusted by adding a
file with cable adjustment values.
• Antenna loss: The antenna usually has internal losses. This is adjusted by adding a
file with antenna adjustment values.
• Other: ”Other” can be used for adding other adjustments values if necessary.
4.2.6.4
Go to value
The go to value menu is used for moving the marker to a specific value on the strength axis
(y). The menu is shown in 4.35
Figure 4.35: The strength go to value menu is used for moving the marker to a specific value on
the y-axis.
4.2.6.5
Step up
Moves the marker by one step up with the amount specified in strength options (Section
4.2.6.1).
4.2.6.6
Step down
Moves the marker by one step down with the amount specified in strength options (Section
4.2.6.1).
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4.2.7
Chapter 4. Results
Calibration
Under this menu the user can choose to open specific PDF documents within the program.
The idea is to have documents with simplified procedures for conducting calibrations and
measurements according to the different standards. These could then be used as guide lines
when using the system.
Figure 4.36: Calibration menu with information from previously conducted calibrations and stipulated procedures for current standards.
4.2.7.1
DO160-F/MIL/IEC
The documents are revised versions of the standards that could be used as guidance when
calibrating the chamber or running tests.
4.2.8
Plot
The menu (Figure 4.37) consists of four submenus enabling export of sweep data, settings
for saving and plotting and closing of all plot windows.
Figure 4.37: The plot menu and its selectable events and submenus.
4.2.8.1
Export data
Under ”Export Data” the user has the possibility to export measurement data to either a
text or Excel document. When exporting data to an Excel file the program automatically
starts, sets up columns with measurement data and generates a plot. This makes it easy to
switch between quantities in the plot window and compare results.
4.2.8.2
Settings
Under the ”settings” menu are three tabs with settings for saving measurement data. Under the one called ”Markers” the user can choose the directory and file name for marker
information gathered during chamber runs. Stored data are field strength, frequency and
comments for each marker set in the plot window. Filename and directory can also be
chosen for the text file under the second tab. Under the third tab the user can choose the
title and label for the plot that is generated when exporting data to Excel.
4.2. RC software
4.2.8.3
65
Close All
The menu option ”close all” closes all open plot windows. There is also a fast button for
this on the tool bar next to the plot buttons.
4.2.9
View
The view menu (Figure 4.38) gives the possibility of hiding or showing tool bar and menu
strip.
Figure 4.38: Menu enabeling hide/show option for tool bar and status strip.
4.2.9.1
Toolbar
The user can choose whether to hide or show the tool bar.
4.2.9.2
Status Bar
The user can choose whether to hide or show the status bar.
4.2.10
Help
The menu (Figure 4.39) gathers help files and information around the program and its
content.
Figure 4.39: The help menu and its selectable submenus.
4.2.10.1
Program content
Here .NET can really show its potential in the form of a search application for the help
files. The help files are written in external text files which at start up are loaded into the
program. Under the menu ”Program Content” there is a text box gathering all the help
files together in one scrollable textbox. To the left there is a list with the topics of all the
help files. By selecting the topic in the list and pressing the ”Show” button, the text box
automatically scrolls down to the specific help file topic. The same thing can also be done
by just double clicking the topic in the topic list.
If the user is looking for a specific word or sentence the search field can be used. If the
user, for example, makes a search for a sentence and it is found, the textbox automatically
scrolls down to the line where that sentence was first found. At the same time, if any of the
66
Chapter 4. Results
words in the sentence are found within the text, they are marked with the color blue. If the
sentence is found on another line the user can just press the search button again and the
textbox will scroll down to the next line. When there is nothing more to be found in the
text the user will be alerted with a ”Search Ended” message and the textbox will scroll up
to the top. If the user wishes to clear the search field and reset the text box, the ”Clear”
button can be used. The application can be seen in Figure 4.40.
Figure 4.40: Help menu to view and search through help files.
4.2.11
Equipment
4.2.11.1
Instrument communication
The following instruments are used during the project:
• RF generator - HP E8257D:
• spectrum analyzer - HP 8566B:
• Pre selector - HP 85685A:
All communication with the instruments was carried out with GPIB commands. GPIB
stands for general purpose interface bus and is designed to connect computers with instruments, which is supported in VEE 9.0. Sending GPIB commands to an instrument through
VEE is done by using an object given in VEE to send instrument commands. Figure 4.41
shows the instrument communication object.
4.2. RC software
67
Figure 4.41: Instrument communication object i VEE.
By using this object it is only the address and the actual command that needs to be set.
RC is using the same object for all instrument communication by dynamically changing
the address to the wanted instrument before sending the command. Figure 4.42 shows the
instrument communication flow.
Figure 4.42: Instrument communication flow in RC.
4.2.11.2
Stirrers communication
The control system running the stirrers (excluding the actual paddles) consists of an ACR9000
Motion Controller communicating with a Packaged Microstepping System, both manufactured by the company Parker Hannifin. The control function is through high-level commands
distributed from the host controller, in our case a desktop computer, to the motion controller. The motion controller in a multi-axis system may then control several drives and
motors. The Packaged Microstepping System consists of a stepper drive together with the
actual motor. Generally, the task of the drive is to supply electrical power to the respective
motor after interpretation of low-level signals from the controller.
• ACR9000 Motion Controller
The ACR9000 is a compact motion controller for controlling servo and stepper drives.
The indexer/controller determines the motor actions like speed, distance, direction,
and acceleration rate. It is designed to enable direct panel-mounting and supplying
multiple connection options.
Main features of the controller are:
◦ Up to 8 axes of servo or stepper control
◦ Advanced Multi-tasking of up to 24 simultaneous programs
68
Chapter 4. Results
◦ interpolation of 8 axes in any combination
◦ 10/100 Base-T Ethernet
◦ USB 2.0
◦ Ethernet/IP compatibility
◦ Absolute Encoder support via SSI
◦ ACR-View Software Development Kit
◦ 24 VDC optically isolated onboard inputs and outputs
◦ CANopen expansion I/O
◦ 120/240 VAC power input
◦ CE (EMC & LVD), UL, cUL approval
• S, SX & SXF Series Packaged Microstepping System
The packaged standalone drive/indexer system can perform registration moves as well
as complex move profiling.
Main features of the system are:
◦ Torques from 65 to 1,900 oz-in
◦ Speeds to 50 rps (3,000 rpm) continuous
◦ 16 user selectable motor resolutions to 50,800 steps/rev
◦ Three-state current control for reduced motor heating
◦ User-selectable current waveform for smooth operation
◦ Zero phase input resets phase currents to the power up positions
◦ Fault output for remote signaling and diagnostics
◦ Optically isolated step and direction, shutdown and zero phase inputs
◦ Anti-resonance eliminates mid-range instability
4.2.12
Software to Controller communication
As stated above there is a versatility of server connections for the controller. For this application we have used Ethernet to communicate with the ACR9000. A .NET wrapper (by
the controller manufacturer denoted ”Motion COMponents”) is then used to synchronize
the programming software and controller to gain access to a DLL (ComACRsrvr.dll) file.
A wrapper is a subroutine that translates a library’s existing interface into a compatible
interface which ultimately enables cross language communication with the DLL file. A DLL
(Dynamic linked library) file is a Microsoft ”shared library” file which in this case holds subroutines for communication with the controller. A restriction for the application software is
for it to be compatible with Microsoft protocol OLE (Object Linking and Embedding) and
COM (Component Object Model) interface standard.
The concept of interaction between the programming software and the control system is
illustrated in figure 4.43
4.2. RC software
69
Figure 4.43: Diagram showing the interaction between application and controller.
In communication with the controller, specific actions can be initiated both through function calls and through direct communication with the controller terminal.
As the controller holds a flash memory it can store code segments and programs which then
can be actively executed. There are routines which enables uploading of code from a text
file to the controller memory. The internal programming language for the controller is called
”AcroBASIC” and consists of simple ASCII mnemonic commands to interact with controller
parameters and bits.
70
Chapter 4. Results
Chapter 5
Conclusions
Looking back at the major parts of the goals there was definitely a satisfactory outcome
regarding the instrument and stirrer communication, as well the look and functionality of
the user interface. The achievement of implementing two out of three standards in the program can be discussed, as the program cannot execute a real measurement yet, but fulfills
a lot of criteria to do it. Not being in the position to be able to use the program for a real
measurement at the end of the project was obviously unsatisfying.
The instrument communication works as planned. It fulfills the demand of a flexible solution where instruments often change. It uses driver text files for the GPIB commands where
sequences of commands can be specified. This lets the user prepare driver files for different
instruments and just change the driver file within the program. The RF generator driver file
has been extended to include limitations for certain instrument parameters, which needs to
be included for other instrument driver files. During the project three types of instruments
have been implemented and tested. The standards require use of more instruments which
should be easy to implement into the program with the use of current functions.
The system in its current form flashes a program into the controller memory which is then
executed when initiating a frequency sweep. The execution of the program located on the
controller is controlled by direct communication with the controller terminal. In the same
way as there are function commands for loading programs from text files into the controller
memory there are several other usable functions and terminal commands for extracting data
and direct stirrer movement. Hence it should be possible to control all movement of the
stirrers with function calls and direct terminal commands and to have the whole program
sequence within Agilent VEE. However, during program development this generated unexpected errors to the extent that it became excluded.
The interfaces tested with the controller are USB and Ethernet. To be able to access a
control function one has to connect to a class defining that control. To communicate with
the controller terminal one has to connect to it as well. A difference between USB and
Ethernet is that with Ethernet the program can stay connected to all classes and the terminal simultaneously when communicating with the controller. Using USB the program
can only stay connected to one class or the terminal at any time. This forces the program
to connect and disconnect, respectively, before and after the controller command. As seen
during the program development, running a series of commands rapidly with USB connec71
72
Chapter 5. Conclusions
tion tends to generate unexpected errors, probably because of communication delays. This
is mainly the reason why the code for the program is only compatible with Ethernet in
its current form. Hence, to be able to use a USB connection, connect and disconnect communication must be added to the program at the cost of stability and maybe program speed.
One of the settings for the stirrers is the number of steps per revolution. Choosing four
steps per revolution will result in four steps taken each being 90 deg. The user can also
choose the number of revolutions to run per frequency which literary multiplies the number of steps with the revolution number. The reverberation chamber at Combitech AB is
equipped with two stirrers. If tuning is run and both stirrers are active the stirrers will
take turn in stepping. This means that when choosing four steps per revolution with two
stirrers the stirrers will step only half of a physical revolution per revolution set in the program software. Hence getting one full rotation for both stirrers per frequency would in this
case require the user to choose two revolutions. Taking odd steps per one revolution and
frequency with two stirrers will result in the starting stirrer taking the first and last step at
each frequency. To alter the starting paddle for every frequency would consequently require
the code to be changed from its current appearance.
5.1
Discussion
Time planning has definitely been an issue during the project as we were very optimistic
about how much to be able to accomplish within the 20 weeks. Projects during earlier
studies always have a solution and when running into trouble there are always answers and
explanations within short reach. In a real working environment you are far more independent and this is a lesson that has been very valuable and something that will be considered
when planning projects in the future. There are a lot of unforeseen events that can occur
during a project, for instance, delivery time for new components is one example that happened during this project.
Considering the goals maybe they should early have been broken down into more partial goals which would have made the work feel more rewarding when reaching them. This
could also have led to a better overview of project requirements and the time consumption
needed for implementation.
There was not an extensive knowledge around Agilent VEE and its program flow at the
beginning of the project. As we have large experience on Matlab and it is partially integrated within VEE we believed it to be very usable, but we soon discovered that Matlab
is not that compatible with VEE and could not be used as planned. Instead it was the
.NET Framework integration that became really useful. As the project was coming to an
end we could see that more or less the whole program is .NET except for the equipment
connections. Considering this it maybe would have been better to use some other programming environment better suited for .NET programming and not using VEE at all. Agilent
VEE is probably not designed to be used for project this extensive. Its strength is in the
simplicity of quickly setting up connections with instruments and to extract data through
ActiveX objects and thread programming. An indication for this is the fact that there is
not a lot of documentation, code or previous work to be found online. The reason for this
may also partially be that it is hard to document the code in a reasonable way.
5.2. Future Work
5.2
73
Future Work
There is no doubt that the current system, including program software, has the capacity
and ability to be expanded to fulfill measurements stipulated in the EMC standards in question. Getting there still demands the program to update the handling of sequential data
flow within Agilent VEE in an effective way. With sequential execution the problem comes
of running parallel events and VEE:s answer to this is to divide code into different thread
objects. Though handling threads and parallel events was definitely not as simple as first
expected, resulting in a lot of unexpected errors and communication problems. When running threads you can’t have code within the thread that is too dependent on code outside, as
it should run independently of other parts of the program. This adds a lot of complexity to
the programming and, as the documentation is limited, a good solution to handle this issue
was never really found. The way of handling communication with thread objects has been
through global objects but there are still questions as to how independent the thread objects
need to be. Trying to use the Matlab engine within thread objects only led to unexpected
errors.
Before the program software can be considered ready for live measurements, extensive error test should be done to secure that there are no bugs or loose threads. This is crucial,
as measurement and testing equipment can be very sensitive and valuable, and the field
strength within the chamber can reach dangerously high levels. As the program software is
connected with the amplifier stage and the corresponding sending antenna, caution should
also be taken as theoretical assumptions have been made to calibrate the software to the
amplifier. Logical updates to the program code, enhancing the speed of finding the desired
field strength with the amplifier, can be made. Future live measurements with subsequent
updates and adjustments are also important.
The user-interface for the program is well-developed though there is always room and abilities for updates. The current program layout lets the user choose standard and type of
measurement at start up. The intention was to have the program automatically adjust
settings that are crucial to the standard chosen. However, setting the values has not been
implemented yet because of lacking time. As Agilent VEE lets the constructed program
be run as an executable the thought was to link to all drivers and files in reference of the
executable file. This would mean that the program could be installed with one install file
on any computer having the runtime version. Some work is still needed, mainly in changing
and generalizing links within the program code.
74
Chapter 5. Conclusions
References
[1] M. Bäckström; O. Lundén; P.-S. Kildal. Reverberation Chambers for EMC Susceptibility
and Emission Analyses. Wiley-Interscience, John Wiley & Sons, Inc, New York, 2002.
Review of Radio Science 1999-2002, Chapter 19.
[2] Paul R. Clayton. Introduction to Electromagnetic Compatibility. John Wiley & Sons,
Inc, 1992.
[3] Staffan Johansson; Per Carlsson. Modern elektronisk mätteknik. Liber AB, first edition,
1997.
[4] ZTEC Instruments Inc. Waveform generator fundamentals. Internet, 2009. http:
//www.ztecinstruments.com/waveform-generator-fundamentals.
[5] Tom Harris. How amplifiers work. Internet, 2008. http://www.howstuffworks.com/
amplifier.htm.
[6] Zhong Chen. Emc antenna fundamentals. Internet, 2007. http://www.conformity.
com/artman/publish/printer_49.shtml.
[7] Robert E. Collin. Foundations for microwave engineering. McGraw-Hill, Inc, 1966.
[8] Carl Nordling; Jonny Österman. Physics Handbook for Science and Engineering. Studentlitteratur, Lund, seventh edition edition, 2004.
[9] M. Bäckström; J. Lorén; G. Eriksson; H-J Åsander. Microwave Coupling into a Generic
Object. Properties of Measured angular Receiving Pattern and its Significance for Testing. in Proceedings of the 2001 IEEE International Symposium on Electromagnetic
Compatibility, Montreal, Canada, .
[10] Richard L. Scheaffer; James T. McClave. Probability and Statistics for Engineers.
Wadsworth Publishing Company, fourth edition, 1995.
[11] Seemant Teotia. Saddlepoint approximation for calculating performance of spectrumsliced wdm systems. Master’s thesis, Virginia Polytechnic Institute and State University, Blacksburg, Virginia, July 1999. Appendix B:93-94.
[12] Harima Katsushige; Sugiyama Tsutomu; Yamanaka Yukio; Shinozuka Takashi. Total
radiated power of radio transmitters measured in a reverberation chamber. Journal of
the National Institute of Information and Communications Technology, Vol.53 No.1:71–
73, 2006.
[13] Gilbert M. Masters. Renewable and efficient electric power systems. Wiley-Interscience,
John Wiley & Sons, Inc, New Jersey, 2004.
75
76
REFERENCES
[14] John D. Kraus. Antennas. McGraw-Hill, Inc, second edition, 1988.
[15] O. Lundén; M. Bäckström. Pulsed Power 3 GHz feasibility study for a 36,7 m3 Mode
Stirred Reverberation Chamber. IEEE International Symposium on EMC, Hawaii, USA,
July 8-13 2007.
[16] Prasad V. Kodali. Engineering Electromagnetic Compatibility : principles, measurements, technologies, and computer models. Institute of Electrical and Electronics Engineers, Inc, 2001.
[17] RTCA, Inc. RTCA/DO-160F : Environmental Conditions and Test Procedures for
Airborne Equipment, December 6 2007. Section 20, Radio Frequency Susceptebility
(Radiated and Conducted).
[18] RTCA, Inc. RTCA/DO-160F : Environmental Conditions and Test Procedures for Airborne Equipment, December 6 2007. Section 21, Emission of Radio Frequency Energy.
[19] Michel V. Ianoz; Torbjörn Karlsson; Frederick M. Tesche. EMC Analasis Methods and
Computational Models. John Wiley & Sons, Inc, 1997.
[20] Department of Defence, United States of America. MIL-STD-461-F : Interference Standard, December 10 2007. Requirements for the control of electromagnetic interference
characteristics of subsystems and equipment.
[21] dmoz open directory project. Visual programming launguages. Internet, 2009. http:
//www.dmoz.org/Computers/Programming/Languages/Visual/.
[22] Paul J. Morrison.
Flow-based programming.
jpaulmorrison.com/fbp/index.shtml.
Internet, 2009.
http://www.
[23] Inc Agilent Technologies. Information and data on agilent vee. PDF, September 1,
2008. http://cp.literature.agilent.com/litweb/pdf/5989-9641EN.pdf.
[24] Microsoft Corporation. .net framework conceptual overview. Internet, 2009. http:
//msdn.microsoft.com/sv-se/library/zw4w595w(en-us).aspx.
[25] Chancey Mathews.
Common language infrastructure.
Internet, June 6
2007. http://en.wikipedia.org/wiki/File:Overview_of_the_Common_Language_
Infrastructure.png.
[26] Inc Agilent Technologies. Information and data on agilent vee. PDF, October 1, 2008.
http://cp.literature.agilent.com/litweb/pdf/5989-9833EN.pdf.
Appendix A
Tables
Frequency Range
fs to 4fs
4fs to 8fs
Above 4fs
Number of required log spaced frequencies
50 per decade
50 per decade
20 per decade
Table A.1: Reverberation test criterion [17].
Tuner Steps
9
10
12
18
20
24
30
36
40
45
60
90
120
180
R
1.957
2
2.08
2.25
2.3
2.38
2.47
2.54
2.59
2.64
2.76
2.92
3.04
3.2
Table A.2: Maximum to average ratio of squared magnitude of E-field [17].
77
78
Chapter A. Tables
Frequency Band
6dB Bandwidth(BW)
0.150 - 30 MHz
30 - 100 MHz
100 - 400 MHz
0.4 - 1 GHz
1 - 6 GHz
1KHz
10KHz
10KHz
100KHz
1MHz
Minimum
sweep time
for
frequency band
(seconds)
N/A
N/A
9
1
1
Minimum
measurments time for
analog
measurement receivers
0.015 sec/KHz
1.5 sec/MHz
1.5 sec/MHz
0.15 sec/MHz
15 sec/GHz
Table A.3: Susceptibility scanning [18].
Frequency Range
30 Hz - 1 MHz
1 MHz - 30 MHz
30 MHz - 1 GHz
1 GHz - 40 GHz
Analog Scans Maximum Scan Rates
0.0333 f0 /sec
0.0667 f0 /sec
0.00333 f0 /sec
0.00167 f0 /sec
Stepped Scans Maximum Step Size
0.05 f0
0.01 f0
0.005 f0
0.0025 f0
Table A.4: Susceptibility scanning [20].
Frequency Range (MHz)
200-300
300-400
400-600
above 600
Tuner Positions
50
20
16
12
Table A.5: Required number of tuner positions for a reverberation chamber [20].
79
Figure A.1: Radiated susceptibility test levels versus category [17].
80
Chapter A. Tables
Appendix B
Figures
Figure B.1: Suitable probe location for chamber calibration [17].
Figure B.2: Standard deviation curve for field uniformity confirmation [17].
81
82
Chapter B. Figures
Figure B.3: Maximum Level of Radiated RF Interference - Category B and L [18].
Figure B.4: Maximum Level of Radiated RF Interference - Category M [18].
Figure B.5: Maximum Level of Radiated RF Interference - Category H [18].
83
Figure B.6: Maximum Level of Radiated RF Interference - Category P [18].
84
Chapter B. Figures
Appendix C
Work Distribution
C.1
Theory
General theory has been divided in the sense that each of us has taken responsibility of
gathering the necessary information and writing about his part. However getting an overall
theoretical understanding is important and there has been a lot of discussion and collaboration in order to understand major concepts of the theory. Erik has been responsible for
theory around basic concepts of EMC, chamber statistics, stirrers and programming language and software. Jonny has been responsible for theory regarding basic concepts of a
reverberation chamber, instruments used and theory around antenna measurements. The
first intention was to study one standard each. While working through the standards it
became clear that the standard DO-160F was more extensive than anticipated and harder
to interpret. This resulted in Erik taking care of the radiated susceptibility part of the
DO-160F standard and Jonny covering the radiated emission part of the same standard.
MIL-STD standard was also covered by Jonny as this gave us an even work load and covered theory. More specifically, chapter responsibilities are:
Erik
• Chapter 3.1 - Electromagnetic compatibility
• Chapter 3.2.6 - Stirrer System
• Chapter 3.4 - Field Statistics
• Chapter 3.8.1.1 - Radiated Susceptibility (RS) Test; Alternative Procedure - Reverberation Chamber
• Chapter 3.9 - Agilent VEE
Jonny
• Chapter 3.2 (except for 3.2.6) - Equipment
• Chapter 3.3 - Reverberation chamber
• Chapter 3.5 - Antenna factor
• Chapter 3.6 - Losses
85
86
Chapter C. Work Distribution
• Chapter 3.7 - E-Field in the Chamber
• Chapter 3.8.1.2 - Radiated Emissions (RE) Test; Alternative Procedure - Reverberation Chamber - mode stirring
• Chapter 3.8.2 - MIL-STD-461F Standard
C.2
Results
The main result is a program software built up by functions and other elements that has
been built and updated by both students throughout the project. Generally, functions and
menus that regard stirrer communication and movement have been Erik’s responsibility,
whereas functions and menus regarding instrument communication have been Jonny’s responsibility. On many levels there are functions and routines that are connecting the two
areas which make it difficult to specifically say who has done what on a programming level.
Menus that are directly related to the instruments are ”Strength” and ”Frequency” which
are under Jonny’s responsibility. Menu ”Stirrers” is in the same way directly related to the
stirrers and under Erik’s responsibility. The ”Help” menu is also developed mainly by Erik.
More specifically, chapter responsibilities are:
Erik
• Chapter 4.2.4 - Stirrer
• Chapter 4.2.10.1 - Help
• Chapter 4.2.11.2 - Stirrer communication
Jonny
• Chapter 4.2.3.4 - Devices
• Chapter 4.2.5 - Frequency
• Chapter 4.2.6 - Strength
• Chapter 4.2.11.1 - Instrument communication