ELINT: The Interception and Analysis of Radar Signals (The Artech House Radar Library)

469 Pages·2006·16.98 MB·English

by  Richard G. Wiley

ELINT

The Interception and Analysis of Radar Signals

For a listing of recent titles in the Artech House
Radar Library, turn to the back of this book.

ELINT

The Interception and Analysis of Radar Signals

Richard G. Wiley

Library of Congress Cataloging-in-Publication Data
Wiley, Richard G.
ELINT: the interception and analysis of radar signals / Richard G. Wiley.
p. cm.—(Artech House radar library)
Includes bibliographical references and index.
ISBN 1-58053-925-4 (alk. paper)
1. Radar.
I. Title.
II. Series.

TK6575.W55
2006
621.3848—dc22
2005058854

British Library Cataloguing in Publication Data
Wiley, Richard G.
ELINT: the interception and analysis of radar signals.—(Artech House radar library)
1. Electronic intelligence
2. Radar
3. Signal detection
I. Title
621.7’34

ISBN-10: 1-58053-925-4

Cover design by Igor Valdman

� 2006 ARTECH HOUSE, INC.
685 Canton Street
Norwood, MA 02062

All rights reserved. Printed and bound in the United States of America. No part of this
book may be reproduced or utilized in any form or by any means, electronic or mechanical,
including photocopying, recording, or by any information storage and retrieval system,
without permission in writing from the publisher.
All terms mentioned in this book that are known to be trademarks or service marks
have been appropriately capitalized. Artech House cannot attest to the accuracy of this
information. Use of a term in this book should not be regarded as affecting the validity of
any trademark or service mark.

International Standard Book Number: 1-58053-925-4
Library of Congress Catalog Card Number: 2005058854

10 9 8 7 6 5 4 3 2 1

Contents

Preface
xiii

CHAPTER 1
Electronic Intelligence
1

1.1
Electronic Intelligence Defined
1
1.2
The Importance of Intercepting and Analyzing Radar Signals
2
1.3
Limitations Due to Noise
4
1.4
Probability of Intercept Problems
4
1.5
Direction Finding (DF) and Emitter Location
5
1.6
Inferring Radar Capabilities from Observed Signal Parameters
5
1.7
Receivers for Radar Interception
6
1.8
Major ELINT Signal Parameters
6
1.9
The Impact of LPI Radar on ELINT
7
References
8

CHAPTER 2
ELINT Implications of Range Equations and Radar Constraints
9

2.1
Range Equations
9
2.2
Radar Constraints
12
2.2.1
Range Resolution Related to Bandwidth
13
2.2.2
Spread Spectrum: Radar Versus Communications
14
2.2.3
Moving Targets and Integration Time Constraints
15
2.2.4
Constraints on Time-Bandwidth Product or Pulse Compression
Ratio
16
2.2.5
Constraints on Doppler Resolution
16
2.2.6
Frequency Agility
19
2.2.7
PRI Agility
19
2.2.8
Power Constraints
23
2.2.9
Pulse Compression Modulation Constraints
23
2.3
Some ELINT Implications of Future Radar Designs
23
2.3.1
Bistatic and Multistatic Radars
24
2.3.2
Radar Trends
24
2.3.3
Wideband Active Adaptive Array Radars
26
2.4
Summary of Radar Design Constraints and Trends
26
2.5
High-Power Microwave Weapons
27
References
28

v

vi
Contents

CHAPTER 3
Characteristics of ELINT Interception Systems
29

3.1
Intercept System Characteristics and Functions
29
3.2
Frequency Coverage
30
3.3
Analysis Bandwidth
31
3.3.1
Wideband Radar Signal Trends
33
3.4
Dynamic Range
35
3.4.1
Dynamic Range Requirements
37
3.5
Sensitivity
39
3.5.1
Noise Figure Measurement
40
3.5.2
Y-Factor Measurement
41
3.5.3
Some Sensitivity Measures
43
3.5.4
Output SNR and Receiver Applications
44
3.5.5
Threshold Detection
45
3.5.6
Sensitivity and the Received Pulse Density
51
3.6
The Ultimate Limits to ELINT Parameter Measurements
52
3.7
ECM and ELINT Receivers
56
3.8
Crystal Video Receivers
56
3.8.1
Crystal Video Applications
59
3.8.2
Postdetection Signal Recording and Sorting
60
3.8.3
CV System Design Considerations
60
3.9
Superheterodyne Receivers
63
3.9.1
Superhet Performance
65
3.9.2
Sweeping Superhet Receivers
67
3.9.3
Tuning Considerations
70
3.9.4
Other Heterodyne Receivers
72
3.10 Instantaneous Frequency Measurement Receivers
74
3.10.1 Limiters Applied to IFMs
74
3.10.2 The Simultaneous Signal Problem
75
3.10.3 CW Signals and IFMs
81
3.10.4 Digitizing the IFM Output
82
3.11 Other Receivers
85
3.11.1 Channelized Receivers
85
3.11.2 Acousto-Optic (Bragg Cell) Receivers
89
3.11.3 Microscan Receivers
90
3.12 System Considerations
93
References
94

CHAPTER 4
Probability of Intercept
97

4.1
Background
97
4.2
Developments in the Theory Behind POI
98
4.2.1
Intercept Description
98
4.2.2
Implications of Today’s Environments/Operations on Intercept
Time
98

Contents
vii

4.2.3
Mathematical Models
100
4.2.4
Recent Developments on POI
108
4.3
Summary
114
References
114

CHAPTER 5
Antennas and Direction Finders
117

5.1
Omni-Directional Antennas
117
5.1.1
Omni-Directional Antenna Applications
117
5.1.2
Parameters for Omni-Directional Antennas
118
5.2
Directional Intercept Antennas
121
5.3
Direction Finding
124
5.4
Instantaneous Direction Finding
126
5.4.1
Amplitude Comparison AOA Measurement
127
5.4.2
Phase Interferometers
131
5.4.3
Bearing Discriminators
139
5.5
Arrays, Lenses, and Subspace DF Methods
144
5.6
Short Baseline TDOA for AOA
145
References
147

CHAPTER 6
Emitter Location
149

6.1
Introduction
149
6.2
Emitter Location Estimation
150
6.3
Deriving the Location Covariance Matrix
152
6.4
Angle of Arrival Location Analysis
153
6.5
Time Difference of Arrival Location Analysis
155
6.6
Time/Frequency Difference of Arrival Location Analysis
159
6.7
Geometric Dilution of Precision
163
6.8
Incorporation of Measurement Error
164
6.9
Summary
167
References
168

CHAPTER 7
Estimating Power at the Transmitter
169

7.1
Power Estimation Through ELINT
169
7.2
Distance to the Horizon
170
7.3
ERP Errors Due to Antenna Pointing Errors
171
7.4
Estimating the Distance to the Radar
174
7.5
Multiple Signal and Multipath Problems
176
7.6
Summary of Power Measurement Requirements
178
7.7
Sample ERP Calculations
179
References
181

viii
Contents

CHAPTER 8
Antenna Parameters
183

8.1
Polarization Defined
183
8.2
Elliptical Polarization
183
8.3
Stokes’ Parameters
185
8.4
Measuring Polarization
187
8.4.1
Polarization Pattern Method
188
8.4.2
Phase-Amplitude Method
189
8.4.3
Multiple Antenna Method
190
8.5
Cross-Polarization
191
8.6
Propagation Effects
194
8.7
System Aspects of Polarization
195
8.8
Antenna Beam Shape
196
8.9
Basic Antenna Pattern Relationships
197
8.10 Beam Patterns from ELINT
199
8.11 Beam Patterns of Array Antennas
205
8.12 Antenna Beam Summary
208
References
209

CHAPTER 9
LPI Radar and the Future of ELINT
211

9.1
What Is LPI Radar?
211
9.2
Radar and ELINT Detection of Signals
212
9.3
Matched Filter Theory
213
9.4
One Interception Strategy: Noncoherent Integration
213
9.5
ESM and Radar Range Compared
214
9.6
Some Pulse Compression Modulation Constraints
217
9.7
Interception Techniques Using the Envelope of the Received Signal
218
9.8
Narrowband Channels and Frequency Modulated Signals
222
9.9
Predetection Processing Methods to Detect Linear FM and Other LPI
Signals
226
9.10 ELINT Receiver Requirements for Interception of Low Peak Power
Signals
232
References
233

CHAPTER 10
Antenna Scan Analysis
235
10.1 Introduction
235
10.2 Some Principles of Searching
236
10.3 Relationships Among Scan Rate, Maximum Unambiguous Range,
and Energy on Target
237
10.4 Fan Beam Scanning: Circular and Sector
239
10.5 Pencil Beam Scanning: Raster, Helical, and Spiral
245
10.6 Tracking Scans and Monopulse
246
10.7 Electronic Scanning
251
10.8 Scan Measurement and Analysis Techniques
252

Contents
ix

10.9 A Three-Dimensional Search Example
253
References
254

CHAPTER 11
Intrapulse Analysis
255

11.1 Introduction
255
11.2 Pulse Envelope Parameters
257
11.3 Envelope Parameter Measurements
258
11.3.1 Rise and Fall Times
260
11.4 Some Radar Performance Limits Related to Pulse Envelope
264
11.5 Multipath Effects
266
11.6 Intrapulse Frequency and Phase Modulation
268
11.6.1 Choosing the Receiver Bandwidth
271
11.7 Intentionally Modulated Pulses
272
11.8 Incidental Intrapulse Shape—Uses and Causes
275
11.9 Comparing Wave Shapes
278
References
280

CHAPTER 12
Pulse Repetition Interval Analysis
281

12.1 Introduction
281
12.2 Common PRI Categories
282
12.2.1 Constant PRI
282
12.2.2 Jittered PRIs
284
12.2.3 Dwell and Switch PRI
285
12.2.4 PRI Stagger
285
12.2.5 Sliding PRIs
286
12.2.6 Scheduled PRIs
286
12.2.7 Periodic PRI Variations
287
12.2.8 Pulse Groups
287
12.3 Time Interval Measurements
287
12.3.1 SNR Limitations
288
12.3.2 Limitations Due to Pulse Amplitude Changes
289
12.3.3 Improving Interval Measurements
292
12.3.4 Digital Thresholding
294
12.4 PRI Analysis Techniques
295
12.4.1 Raster Displays
296
12.4.2 PRI Sounds
297
12.5 PRI Analysis Theory and Practice
298
12.5.1 Statistical Techniques
300
12.5.2 Delta-T Histogram
303
12.6 Interpreting the Results
307
12.6.1 Delay Line PRI Generators
308
12.6.2 Crystal Oscillators and Countdown Circuits
308
12.7 PRI and Range Velocity Ambiguities
313
12.8 MTI Radar Blind Speeds
313

x
Contents

12.9 Moving Target Detection
314
References
315

CHAPTER 13
Deinterleaving Pulse Trains
317

13.1 Pulse Sorting
317
13.2 PRI-Based Gating
319
13.3 Deinterleaving Algorithms
320
13.4 Delta-T Histogram Applied to Deinterleaving
322
13.5 The Pulse Train Spectrum
331
13.6 Combining Pulse Bursts
332
13.7 Raster Displays and Deinterleaving
333
13.8 Measuring Deinterleaver Performance
333
References
334

CHAPTER 14
Measurement and Analysis of Carrier Frequency
335

14.1 Pulsed Signal Carrier Frequency
335
14.1.1 Frequency Measurement Accuracies
335
14.1.2 Doppler Shifts
337
14.1.3 Drift Measurement
337
14.1.4 FM Ranging in Radar
338
14.2 Intrapulse Frequency or Phase Modulation
338
14.2.1 Analysis of Predetection Data
342
14.3 Coherence (Short-Term RF Stability)
342
14.3.1
RMS Phase Fluctuation
346
14.3.2
RMS Frequency Fluctuations
347
14.3.3
Signal Repeatability
350
14.3.4
Effects of Variations in �0
352
14.3.5
Frequency-Domain Stability Measures
353
14.3.6
Bandwidth Limitations on Allan Variance Measurements
354
14.3.7
Noise Limitations on Allan Variance Measurements
356
14.3.8
Frequency Stability Measures for Power Law Spectra
357
14.3.9
Sinusoidal FM and Linear Frequency Drift
359
14.3.10 Short-Look Problem
359
14.4 Frequency Character of CW Signals
361
14.5 Pulsed Signal Example
361
14.6 Measuring Coherence
364
14.7 Effects of Drift
365
References
365

CHAPTER 15
Determining ELINT Parameter Limits
367

15.1 Introduction
367
15.2 Histograms Used to Determine Parameter Limits
367
15.3 Types of Histograms
370

Contents
xi

15.4 Two-Sigma Parameter Limits
373
15.5 Histogram Analysis Techniques
375
15.5.1 Parameter Limits Example
375
15.5.2 Intercepts Separated into Accuracy Classes
377
15.5.3 Most Probable Values
378
15.6 Analysis Problems
379
15.6.1 Signal Identification Errors
379
15.6.2 Transforming Parameters and Their Accuracies
379
15.7 Histogram Analysis Summary
381
References
382

CHAPTER 16
ELINT Data Files
383

16.1 Introduction
383
16.2 Signal Identification
385
16.3 ELINT Data for Radar Warning Receiver Design
386
16.4 ELINT Data for Simulation and Training
388
16.5 Adding Non-ELINT Data
388
16.6 Summary
389
Reference
389

APPENDIX A
Spectrum Widths: 3-dB and First Nulls for Trapezoidal Pulses
391

A.1
Introduction
391
A.2
Rectangular Pulses
391
A.3
Trapezoidal Pulses: Equal Rise and Fall Times
391
A.4
Trapezoidal Pulses: Unequal Rise and Fall Times
393

APPENDIX B
Some ELINT Considerations of FM Signals
395

B.1
Introduction
395
B.2
Effects of Sinusoidal Interference on Phase- and Frequency-
Demodulated Signals
395
B.3
Signals with Sinusoidal Frequency Modulation
398
B.4
Carson’s Rule
400
B.5
Modification of Carson’s Rule for ELINT Applications
401
B.6
FM Demodulation Degradation by RF Band Limiting
403
B.7
Effects of Noise on FM Demodulated Signals
408
References
412

APPENDIX C
A Frequency Hop Radar Example
413

C.1
Probability That One or More Pulses Occur at the Desired Frequency
413
C.2
Probability That Exactly One Pulse Occurs at the Desired Frequency
414
C.3
Probability That Exactly k Pulses Occur at the Desired Frequency
415

xii
Contents

C.4
Probability That Several Pulses Occur at the Desired Frequency Less
Than G Pulses Apart
415
C.5
Probability Distribution of the Interval Between Two Pulses
418
C.6
Determining an Optimum Receiver Sweep Rate
427

APPENDIX D
History and Fundamentals of the IFM
429

D.1 The Broadband Microwave Frequency Discriminator
433
References
439

APPENDIX E
Emitter Location Partial Derivatives
441

About the Author
445

Index
447

Preface

More than 20 years have passed since the publication of Electronic Intelligence:
The Analysis of Radar Signals (Artech House, 1983) and Electronic Intelligence:
The Interception of Radar Signals (Artech House, 1985). Much of what those
books contained remains valid today. With this new book, I have again avoided
emphasizing specific hardware and software currently available because it changes
too rapidly. My hope is that this book remains useful for the next 20 years. This
book is partially based on my earlier works, Electronic Intelligence: The Analysis
of Radar Signals (Artech House, 1983), Electronic Intelligence: The Analysis of
Radar Signals, Second Edition (Artech House, 1993), and Electronic Intelligence:
The Interception of Radar Signals (Artech House, 1985).
It is appropriate to list those people who introduced me to the exciting field
of ELINT and who continue to provide insights and inspiration. Professor E. M.
Williams of Carnegie-Mellon University introduced me to the field. Dr. Thomas
F. Curry provided my early training. Both are now gone but often remembered.
There is no way to adequately recognize the contributions of Robert B. Shields,
my friend and business associate for more than 45 years. He always grasps the
‘‘big picture’’ and asks the right questions at the right time.
For their contributions to this book, I am grateful to Arthur Self for his work
on Chapter 4 and to Charles Estrella for his work on Chapter 6.
I am also grateful to the many people who work in ELINT and who have
shared their experiences and insights with me. This includes not only my coworkers
at Research Associates of Syracuse, Inc., but also the several thousand people who
have attended continuing education courses I have presented over the past 20
years—many for the Association of Old Crows. The struggle to answer their
questions is one of the motives in writing this book.
The continued support of my wife, Jane, and the good start in life provided
by my parents Mildred and Asa (1911–1995) were key to the creation of this book.
I am also thankful for the support of my six children, their spouses, and our 13
grandchildren. Many of them are now in their teens and approaching adulthood.
It is my hope and prayer that vigilance through ELINT and other means helps
keep them and all children everywhere in safety and freedom.

‘‘Lord God Almighty, in whose Name the founders of this country won liberty
for themselves and for us, and lit the torch of freedom for nations then unborn:
Grant that we and all the people of this land may have grace to maintain our
liberties in righteousness and peace. . . .’’

—Collect for Independence Day, page 241, The Book of Common Prayer (1979)
According to the use of the Episcopal Church

xiii