Use or disclosure of the information contained herein is subject to the restrictions on the Cover...
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Use or disclosure of the information contained herein is subject to the restrictions on the Cover Page Lockheed Martin Aeronautics Company 1 Copyright 2006 by Lockheed Martin Corporation. CURRENCY NOTICE: A hard copy of this document may not be the document currently in effect. The current version is always the version in the Lockheed Martin Network. Evaluating and Improving Radiated Immunity Test Systems Performance John D. Osburn
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Use or disclosure of the information contained herein is subject to the restrictions on the Cover PageLockheed Martin Aeronautics Company
1
Copyright 2006 by Lockheed Martin Corporation.
CURRENCY NOTICE: A hard copy of this document may not be the document currently in effect. The current version is always the version in the Lockheed Martin Network.
Evaluating and Improving Radiated Immunity Test Systems Performance
John D. Osburn
2
Use or disclosure of the information contained herein is subject to the restrictions on the Cover PageLockheed Martin Aeronautics Company
Introduction
Purpose — This presentation is intended to: a.) review basic immunity system design, and
b.) identify serious issues in system design and
c.) suggest possible corrections for these problems.
Scope — The discussion is limited to the test equipment setup. Other problems such as test system interaction with the test environment and monitoring for immunity failures are not discussed.
3
Use or disclosure of the information contained herein is subject to the restrictions on the Cover PageLockheed Martin Aeronautics Company
Purpose of Immunity or Susceptibility Testing
Determine if EUT responds to incident electromagnetic radiation at a specific level. Failure to respond to specified electromagnetic levels “assures” continued proper operation of the EUT in a hostile electromagnetic ambient environment.
Standard conditions of testing and test equipment performance are required to allow inter-comparison of test results, between labs and over time.
Use or disclosure of the information contained herein is subject to the restrictions on the Cover PageLockheed Martin Aeronautics Company
4
Copyright 2006 by Lockheed Martin Corporation.
CURRENCY NOTICE: A hard copy of this document may not be the document currently in effect. The current version is always the version in the Lockheed Martin Network.
Immunity Test System Design
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The Immunity Test Equipment Setup
The list of test equipment for immunity testing is straight forward, and can be derived from the requirements of IEC 61000-4-3
The specific list of required equipment is: RF Signal Generator Power Amplifier Linearly Polarized Radiating Antenna Power Level Measurement Device
Optional Equipment Low Pass or Band Pass Filters
6
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Idealized Immunity Test System Block Diagram
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Idealized E-Field Generation Test System Equipment and Function
Signal Generator - Source of test signal, amplitude to 0 dBm and frequency, 80 - 1000 MHz, 80% AM w/ 1 kHz sinusoid
Amplifier - Increases level of test signal to achieve desired test field values
Forward/Reverse Power Coupler - Samples forward and reflected power to radiating device
Power Meter - Reads power values in forward and reverse channels, allows calculation of net forward power to antenna (radiated power)
Antenna - Generates test field at 3 m Field Meter - Reads generated field levels, provides feedback
loop
8
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Immunity Test System Design
The basic design equation is:
Note that all values of the design equation are functions of frequency, and linear performance is implied. Cable losses are neglected.
E dB V m SG dB V AG dB TAF dBmout( / ) ( ) ( ) ( ) 1
where:E dB V m( / ) = The E-field test levelSG dB Vout ( ) = The signal generator outputAG dB( ) = Amplifier gainTAF dBm( ) 1 = The transmit antenna factor
TAF dbm G dB d mi( ) ( ) . log[ ( )] 1 2 22 20
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Fundamental Test System Design:Frequency Coverage
Test System operating range is set by the operating range of the components
1 10 100 1000
Boonton 9200A
AR 10W1000
NARDA 3020
HP 8642A
EMCO 7100
Probe Subsystem Response
Power Meter Response
Power CouplerResponse
Amplifier Response
Signal Generator Response
Frequency, MHz
Valid SystemResponse
10
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Fundamental Immunity System Design RF Power Requirements
DESIRED FIELD= 10 V/m= 140 dB µV/m
TAF=-8.66 dB m-1
Vin = 148.66 dB µV
SGout = 101dB µV = -7 dBm
Summary of Input Power Allowances for Sizing an Amplifier
Factor Allowance (dB)VSWR 2:1 1True Linear operation 1Calibration Distance 2.5Modulation Allowance 5.1TOTAL 9.6
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Idealized Equipment Performance - Signal Generator
Generates basic signal Requires at least 0.X dBm
resolution for amplitude for calibration of test setup
dB µV setting desirable for greater resolution of output
Level at reference point must be within -0, +10% or lower to achieve -0, +6 dB calibration
Must cover frequency range Must provide 80% AM
12
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Idealized Equipment Performance - Power Amplifier
Wide bandwidth power amplifiers have large ripple values, as much as 4 dB
Rated gain is typically at 0 dBm input (maximum value of input)
Linear gain region is at 1 dB compression
Maximum gain is at saturation (increase in input produces no increase in output)
Should operate in linear region for repeatable results
13
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Idealized Equipment Performance - Antenna
Two important parameters of antenna, Transmit Antenna Factor, and input VSWR
TAF is evaluated at a specific distance, under specific conditions
VSWR should be 2:1 for optimum results, giving 1 dB error
TAF dBmr
Gi( ) . 1 10 6
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Theoretical Probe System Response
Probe system used diode detector, loses frequency information
Responds to sum of all signals present
Must use calibration factors for adequate accuracy
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Other System Component Constraints
Cables should have transmission and reflection loss measured periodically
Very short cable from the F/R coupler to the antenna, compensate for cable loss in design
Do NOT over tighten RF connectors Antenna mount should be non conducting Cable should be routed straight back from transmit
antenna for 2 m for repeatability Once calibration complete, position of antenna, etc., very
important
16
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Summary of Fundamental System Design
Fundamental design allows: Definition of equipment requirements Selection of equipment Establishing of basic operating parameters
Many or even most immunity test system designs are felt to be complete at this point
Use or disclosure of the information contained herein is subject to the restrictions on the Cover PageLockheed Martin Aeronautics Company
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Copyright 2006 by Lockheed Martin Corporation.
CURRENCY NOTICE: A hard copy of this document may not be the document currently in effect. The current version is always the version in the Lockheed Martin Network.
Practical Issues in
Immunity Test System Design
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Technical Issues
Begins with fundamental design complete Addresses:
Non ideal performance of sub-system components Interaction between non-ideal components
Assures test repeatability and meaningful inter-lab comparisons
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Signal Generator Non-Ideal Characteristics
Significant harmonics of the fundamental can be present Transient behavior on switching in amplitude and/or
frequencies Inadequate resolution for precision control during
calibration
20
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Real Performance - Signal Generator Output
0 200 400 600 800 10000
20
40
60
80
100
Third harmonic = 50.2 dB µV
Second Harmonic = 56.7 dB µV
Output = 102 dB µV
Sig
nal G
ener
ator
Out
put,
dB
µV
X axis title
1st Harmonic is 46 dB down
12 Discernible harmonics present
21
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Signal Generator Switching Characteristics
12 dB Overshoot
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Power Amplifier Non-Ideal Performance Characteristics
Gain varies over as much as 9 dB range (1 dB compression values)
17 + discernible harmonic signals present Non-saturated output assumed Linear operation assumed
23
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Amplifier Gain vs Frequency
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Real Performance - Power Amplifier with Some Signal Generator Harmonics present
0 200 400 600 800 1000
40
60
80
100
120
89.4 dB µV
90.6 dB µV
119.1 dB µVV
olta
ge
outp
ut,
dB µ
V
Frequency, MHz
1 st harmonic is -29 dBc
96 dB µV
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Test Signal Generation Antenna Performance
Antenna - free space mismatch is large below 80 MHz
Ideal operation at VSWR 2:1 not possible at frequencies below 120 MHz
Must size amplifier to accommodate VSWR
10 100 10001
10
100
VSW
R, M
odel
314
1Frequency, MHz
2:1
80 MHz
4:1
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Correction for Additional Power Due to Antenna Mismatch
1 100.01
0.1
1
10
100
Ad
ditio
na
l A
pm
lifie
r O
utp
ut
Re
qu
ire
d d
ue t
o m
ism
atc
h,
dB
Load SWR
210
11
1
1log20
SWRSWR
CorrectionSWR
27
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Actual Probe Response
Probe systems respond to all signals present in the environment
If harmonics are present, their value will be added to the fundamental response
The actual indication from the probe is the Peak Envelope power, computed from
nmVdB
iE
real hmVdBE fund
2
]20/)/([20/10log20)/(
28
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Actual Probe Response to Harmonic Rich Spectrum
Probe Reading for this Spectrum
= 121.3 dB µV
Actual Level = 119.1 dB µV
200 400 600 8000
20
40
60
80
100
120
Volta
ge o
utp
ut,
dB
µV
Frequency, MHz
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Actual Probe System Response
ENTER HARMONIC AMPLITUDE
2nd 3rd 4th 5th 6th 7th 8th 9th 10th PEP (dBc) Volts/m
0 -100 -100 -100 -100 -100 -100 -100 -100 6.02 20.00-3 -100 -100 -100 -100 -100 -100 -100 -100 4.65 17.08-6 -100 -100 -100 -100 -100 -100 -100 -100 3.53 15.01-10 -100 -100 -100 -100 -100 -100 -100 -100 2.39 13.16-13 -100 -100 -100 -100 -100 -100 -100 -100 1.76 12.24-17 -100 -100 -100 -100 -100 -100 -100 -100 1.15 11.41-20 -100 -100 -100 -100 -100 -100 -100 -100 0.83 11.00-20 -30 -40 -40 -100 -100 -100 -100 -100 1.23 11.52-18 -25 -28 -35 -40 -100 -100 -100 -100 1.94 12.50-13 -20 -18 -30 -29 -100 -100 -100 -100 3.62 15.17-16 -20 -22 -29 -30 -40 -100 -100 -100 3.02 14.15-18 -19 -21 -23 -20 -22 -40 -40 -40 4.12 16.07-20 -20 -20 -20 -20 -20 -20 -20 -20 5.58 19.00-20 -20 -20 -20 -100 -100 -100 -100 -100 2.92 14.00-20 -20 -26 -26 -100 -100 -100 -100 -100 2.28 13.00-20 -20 -30 -30 -40 -40 -100 -100 -100 2.17 12.83-20 -30 -30 -40 -50 -50 -60 -60 -60 1.46 11.83-30 -30 -30 -30 -30 -30 -30 -30 -30 2.18 12.85-40 -40 -40 -40 -40 -40 -40 -40 -40 0.75 10.90-50 -50 -50 -50 -50 -50 -50 -50 -50 0.24 10.28-60 -60 -60 -60 -60 -60 -60 -60 -60 0.08 10.09-20 -20 -20 -20 -100 -100 -100 -100 -100 2.92 14.00-30 -30 -30 -30 -100 -100 -100 -100 -100 1.03 11.27-20 -30 -28 -38 -50 -50 -100 -100 -100 1.51 11.90-20 -100 -100 -100 -100 -100 -100 -100 -100 0.83 11.00-20 -30 -50 -50 -50 -50 -50 -50 -50 1.24 11.54-25 -32 -50 -50 -50 -50 -50 -50 -50 0.86 11.03
30
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Incorporating Real Equipment Constraints in an Immunity Test Setup
Remember Osburn’s Second Law “Precision is achieved at the cost of complexity.”
Additional subsystem components needed to control equipment problems: Attenuator to control Signal Generator
Switching transients Series of low pass, high power filters to
control harmonic content, improve accuracy, computer switched
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Recommended Test Instrumentation Setup
Signal Generator
Programmable Antenna
Amplifier Switch F/R
0.06-0.12LP
0.12-0.25 LP
0.25 -0.5LP
0.5 -1.OLP
Switch
Power Meter
32
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Continuous Monitoring of Test System Performance`
Addition of a simple sense antenna, at a convenient location, allows a independent measurement of the existence of the test signal
Will probably not read test level, look for changes from signal received during calibration
Assures no harmonic content in test signal Uses readily available existing equipment
Spectrum Analyzer
Limiter30 dBPad
SenseAntenna
33
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Recommendations for Better Immunity Test Setups
Control non-ideal behavior of system components Signal Generator
Transients Harmonics
Amplifier Harmonic generation Gain issues Output power requirements
Probe Sum of all signals response
34
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Summary
Have reviewed fundamental immunity test system design Have identified second tier design problems and
proposed solutions Have looked deeper into issues of immunity testing,
hopefully in an organized manner, to address problems that while recognized, might not have been adequately addressed.
