Misure di compatibilita’
Elettromagnetica
Roberto Sacchi
Electronic Measurements Group
Agilent Technologies
What is EMC?
Electromagnetic Compatibility (EMC): The ability of equipment to operate in its
electromagnetic environment without introducing intolerable disturbances into other
devices.
Combination of Interference and Immunity.
Electromagnetic Interference (EMI):
Electromagnetic energy emanating from one device which causes another device to
have degraded performance.
Electromagnetic Immunity (Susceptibility, EMS): Tolerance in the presence
of electromagnetic energy (Performance degradation due to electromagnetic energy).
Definitions
EMC –
ElectroMagnetic Compatibility
EMI –
ElectroMagnetic
Interference
EMS –
ElectroMagnetic
Susceptibility
(aka Immunity)
Sources of Electromagnetic Interference
• Natural Sources
Lightning
Sun Spots
• Unintentional emitting products
Power lines
Motors (mixers, hair dryers etc)
Lighting, appliances
• Devices that intentionally emit signals
Most computers
Hand held communication devices
Radar, transceivers, broadcast equipment etc
EMI measurement system
EMI receiver minimum requirements
A CISPR 16-1-1 receiver must have the following functionality:
 A normal +/- 2 dB absolute accuracy
 CISPR-specified resolution bandwidths (-6 dB)
 Peak, quasi-peak, EMI average, and RMS average detectors
 Input impedance with a nominal value of 50 ohms
Pre-compliance vs. Full compliance measurements
Pre-compliance measurements
Evaluate the conducted and radiated emissions
of a device using correct detectors and
bandwidths before going to a test house for
compliance testing
Full Compliance measurements
Full compliance testing requires a receiver that
meets the requirements of CISPR part 16-1-1 (for
commercial) or MIL-STD-461 (for military), a
qualified open area test site or semi anechoic
chamber and an antenna tower and turntable to
maximize EUT signals.
Field Strength Unit
Radiated EMI emissions measurements measure the
electric field. The field strength is calibrated in dBμV/m.
Pt = total power radiated from an isotropic radiator
Pd = the power density at a distance from the isotropic radiator
(far field >λ/2π)
Pt
Pd 
4   r 2
R 120  
E2
Pd 
R
Pt
E2

R 4   r 2
[ohm] Free Space Impedance
r
E
Pt  30
r
[V/m]
Field Strength and Antenna factors
Radiated EMI emissions tests measure the electric field. The
field strength is calibrated in dBμV/m.
Antenna factors is the ratio of the electric field (V/m) present
at the plane of the antenna versus the voltage out of the
antenna connector.
Log units:
AF(dB/m) = E(dBμV/m) - V(dBμV)
E(dBμV/m) = V(dBμV) + AF(dB/m)
Notes:
Antenna factors are not the same as antenna gain.
dBμV = dBm + 107
Broadband antenna examples
Double ridged horn antennas
Log Periodic
antenna
Hybrid log periodic
Biconical antenna
Hybrid log periodic
General Process for Making EMI Measurements

Determine the country or countries in which the product
will be sold which in turn identifies the regulator agency.

Select the limit lines to be tested to (conducted/radiated).

Select the band to be used.

Correct for transducer loses and amplifiers gains.

Identify signals above the limit that must be evaluated.

Zoom in on failed signal and perform quasi-peak or
average measurements.
Precompliance Conducted Emissions Setup
To Mains
X-Series Signal
Analyzer
LISN
DUT
With N6141A
EMC App
DUT power cord*
Transient
Limiter
*Keep the power cord short to avoid
becoming an antenna
Precompliance Radiated Emissions Setup
Perform testing in both the
horizontal and vertical position
3 or 10 Meter distance
DUT
X-Series Signal Analyzer
with N6141A EMC App
Ground Plane
The goal is to find and record the maximum emissions from the DUT by rotating the
turn table, changing the polarity and the height of the antenna.
Agilent Solutions
N6141A EMI Measurement Application
PXA
MXA
Pre-compliance
EXA
CXA
Compliance
Agilent MXE N9038A
W/N6141A EMC measurement application
 Full Featured Pre-compliance Application
 Available in all X-Series models