Monopulse Principles and Techniques

419 Pages·2011·5.2 MB·English

by  Samuel M. Sherman

Monopulse Princ ip les and Techn iques
Sec ond Edi tion
For a list ing of re cent ti tles in the Artech House Rad ar Series,
turn to the back of this book.
Monopulse Princ ip les and Techn iques
Sec ond Edi tion
Sam uel M. Sherman
Da vid K. Barton
artechhouse.com
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ISBN-13 978-1-60807-174-6
Cover de sign by Vicki Kane
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10 9 8 7 6 5 4 3 2 1
Contents
Preface to the Second Edition . . . . . . . . . . . . . . . . . . . xiii

Preface to the First Edition . . . . . . . . . . . . . . . . . . . . xv

Chapter 1 Introduction . . . . . . . . . . . . . . . . . . . . . 1
1.1 Review of Radar Principles . . . . . . . . . . . 1
1.2 Tracking Radars and the Evolution of Monopulse . . . 2
1.3 A “Baseline” Monopulse Radar . . . . . . . . . . 6
1.4 Advantages and Disadvantages of Monopulse . . . . 13
1.5 Nonradar Uses of Monopulse . . . . . . . . . . 15
References . . . . . . . . . . . . . . . . . . . . . 16

Chapter 2 Terminology, Definitions, and Notation . . . . . . . . . . 19
2.1 The Meaning of Monopulse . . . . . . . . . . . 20
2.2 Apertures and Illumination Functions . . . . . . . 22
2.3 Patterns, Lobes, and Beams . . . . . . . . . . . 22
2.4 Sum and Difference Patterns . . . . . . . . . . . 24
2.5 Sum and Difference Notation . . . . . . . . . . 26
2.6 Error Signals . . . . . . . . . . . . . . . . . 27
2.7 Complex Signal Representation and Complex
Envelopes . . . . . . . . . . . . . . . . . 27
2.8 Elevation, Azimuth, and Traverse . . . . . . . . . 31
References . . . . . . . . . . . . . . . . . . . . . 38

Chapter 3 The Monopulse Output as a Complex Ratio . . . . . . . . 39
3.1 General Principles . . . . . . . . . . . . . . . 39
3.2 Relative Phase of Difference and Sum . . . . . . . 41
3.3 Some Useful Relationships and Formulas . . . . . . 41
References . . . . . . . . . . . . . . . . . . . . . 44
v
vi Monopulse Principles and Techniques
Chapter 4 Components Used in Monopulse . . . . . . . . . . . . . 45
4.1 Antenna Mounts . . . . . . . . . . . . . . . . 45
4.2 Antennas . . . . . . . . . . . . . . . . . . . 46
4.2.1 Lens Antennas . . . . . . . . . . . . . 47
4.2.2 Single-Reflector Antennas . . . . . . . . 50
4.2.3 Cassegrain (Double Reflector) Antennas . . 51
4.2.4 Polarization-Twisting Reflector Systems . . 52
4.3 Feeds . . . . . . . . . . . . . . . . . . . . 54
4.4 Devices for Forming Sums and Differences . . . . . 57
4.4.1 Hybrid Junctions . . . . . . . . . . . . 57
4.4.2 Directional Couplers . . . . . . . . . . 60
4.4.3 Comparators . . . . . . . . . . . . . 63
4.4.4 Other Methods of Obtaining Monopulse Sum
(or Reference) and Differences . . . . . 65
4.4.5 Graphical Symbols . . . . . . . . . . . 66
4.5 Receivers . . . . . . . . . . . . . . . . . . 68
References . . . . . . . . . . . . . . . . . . . . . 69

Chapter 5 Amplitude-Comparison and Phase-Comparison Classification . 71
5.1 Definitions and Examples . . . . . . . . . . . . 72
5.1.1 Definitions . . . . . . . . . . . . . . 72
5.1.2 Interpretation . . . . . . . . . . . . . 72
5.1.3 Optimum Monopulse . . . . . . . . . . 74
5.1.4 Amplitude-Comparison Monopulse Antenna
Example . . . . . . . . . . . . . . 78
5.1.5 Phase-Comparison Monopulse Antenna
Example . . . . . . . . . . . . . . 80
5.2 Phase Fronts, Phase Centers, and Related Concepts . . 82
5.2.1 Transmitting Antennas . . . . . . . . . 82
5.2.2 Receiving Antennas . . . . . . . . . . 85
5.2.3 Targets . . . . . . . . . . . . . . . 85
5.2.4 An Example: Phase Fronts of a Two-Element
Source . . . . . . . . . . . . . . . 86
5.2.5 Simplification at Large Distances . . . . 87
5.2.6 Phase Centers of Array Antennas . . . . 90
5.2.7 Phase Centers of Reflector Antennas . . . 93
5.3 Distinguishing Between Phase- and Amplitude-
Comparison Monopulse . . . . . . . . . . . . 93
5.3.1 Reflector Antenna Examples . . . . . . 93
5.4 Distinction Based on Relative Phase of Illumination
Functions . . . . . . . . . . . . . . . . . 98
5.5 Distinction Based on Sum and Difference Patterns . . 99
5.6 Apparent Conversion of One Class to the Other . . . .100
Contents vii
5.7 Summary of Amplitude-Comparison and Phase-
Comparison Classification . . . . . . . . . . . 102
References . . . . . . . . . . . . . . . . . . . . . 103

Chapter 6 Optimum Feeds for Space-Fed Amplitude-Comparison
Monopulse Antennas . . . . . . . . . . . . . . . . 105
6.1 Nature of Optimization . . . . . . . . . . . . 105
6.2 f/D Ratio . . . . . . . . . . . . . . . . . . 107
6.3 Effect of Squint Angle in a Four-Horn Feed . . . . 108
6.4 Optimization of Squint Angle . . . . . . . . . . 111
6.5 Comparison with Measured Patterns . . . . . . . 113
6.6 Beacon Operation . . . . . . . . . . . . . . 116
6.7 Comparison of Beam Squint Angle and Feed
Offset Angle . . . . . . . . . . . . . . . . 116
6.8 Effect of Squint Angle on Normalized Difference
Pattern . . . . . . . . . . . . . . . . . . 117
6.9 Other Feed Configurations . . . . . . . . . . . 118
6.10 Summary of Feed Optimization . . . . . . . . . 122
References . . . . . . . . . . . . . . . . . . . . . 123

Chapter 7 Monopulse in Array Antennas . . . . . . . . . . . . . 125
7.1 Principles of Operation . . . . . . . . . . . . 125
7.2 Array Coordinates . . . . . . . . . . . . . . 128
7.3 Arrays with Space Feeds . . . . . . . . . . . . 128
7.4 Arrays with Constrained Feeds . . . . . . . . . 132
7.4.1 Constrained-Fed Arrays Divided into
Quadrants or Subarrays . . . . . . . 132
7.4.2 Constrained-Fed Arrays with Independent
Illuminations . . . . . . . . . . . 134
7.4.3 Efficient Illumination Tapers for Phased
Arrays . . . . . . . . . . . . . . 136
7.5 Classification as Amplitude or Phase Comparison . . 138
7.6 Special Types of Arrays . . . . . . . . . . . . 141
References . . . . . . . . . . . . . . . . . . . . . 141

Chapter 8 Monopulse Processors . . . . . . . . . . . . . . . . 143
8.1 Functions and Properties of Monopulse Processors 144
8.2 Range Gating . . . . . . . . . . . . . . . . 146
8.3 Angular Coordinates for Monopulse Calibration . . 147
8.4 Exact Monopulse Processor . . . . . . . . . . . 148
8.5 Processor Using Phases and Linear Amplitudes of
s and d . . . . . . . . . . . . . . . . . . 150
8.6 Processor Using I and Q . . . . . . . . . . . . 152
viii Monopulse Principles and Techniques
8.7 Processor Using Phases and Logarithmic Amplitudes
of s and d . . . . . . . . . . . . . . . . . 153
8.8 Processor Using Dot-Product Detector with AGC . . 155
8.9 An Approximate Dot-Product Detector . . . . . . 158
8.10 Noncoherent Processor Using Sum and Difference
of |v | and |v | . . . . . . . . . . . . . . . 162
1 2
8.11 Processor Using s + d and s − d . . . . . . . . . 165
8.12 Processor Using log |v | and |v | . . . . . . . . . 166
1 2
8.13 Processor Using s ± jd . . . . . . . . . . . . . 170
8.14 Two-Channel Monopulse Using s + d and s − d . . . 174
8.15 Phase-Amplitude Monopulse . . . . . . . . . . 177
8.16 Multiplexed Monopulse Receivers . . . . . . . . 178
8.17 Conopulse . . . . . . . . . . . . . . . . . 181
8.18 Summary of Monopulse Processors . . . . . . . 182
References . . . . . . . . . . . . . . . . . . . . . 185

Chapter 9 Response to Unresolved Targets . . . . . . . . . . . . 187
9.1 Review of Monopulse Response to a Point Target . . 190
9.2 The Meaning of Unresolved Targets . . . . . . . 191
9.3 Superposition as an Approximation . . . . . . . . 191
9.4 The Two-Target Problem . . . . . . . . . . . . 193
9.5 The Complex Indicated Angle . . . . . . . . . . 195
9.6 Physical Interpretation . . . . . . . . . . . . . 200
9.7 Measurement of the Imaginary Part (Quadrature-
Phase) Component . . . . . . . . . . . . . 201
9.8 Effect of Local-Oscillator Frequency . . . . . . . 203
9.9 Detection of Presence of Unresolved Targets . . . . 203
9.10 Mean and Variance of Indicated Angle . . . . . . 204
9.11 Weighted Mean of Indicated Angle . . . . . . . . 207
9.12 Possibility of Determining Angles of Unresolved
Targets . . . . . . . . . . . . . . . . . . 209
9.13 Information Derivable from Real Part . . . . . . 214
9.14 Removal of Initial Assumptions . . . . . . . . . 216
9.15 Extensions of Monopulse Techniques and
Fundamental Limitations . . . . . . . . . . . 217
9.16 Closed-Loop Tracking . . . . . . . . . . . . . 218
9.17 More Than Two Targets . . . . . . . . . . . . 219
9.18 Nonindependent Targets . . . . . . . . . . . . 221
References . . . . . . . . . . . . . . . . . . . . . 222

Chapter 10 Monopulse Angle Errors . . . . . . . . . . . . . . . 225
10.1 Error Due to Noise . . . . . . . . . . . . . . 226
10.1.1 Analytical Model . . . . . . . . . . 227
Contents ix
10.1.2 Noise Statistics . . . . . . . . . . . 227
10.1.3 Conversion of Voltages to Powers . . . . 229
10.1.4 Conversion of d/s Error to Angular
Error . . . . . . . . . . . . . . 229
10.1.5 Bias in Monopulse Ratio . . . . . . . 231
10.1.6 Exact Solution for Probability Density
Function of d/s . . . . . . . . . . 233
10.1.7 First-Order Approximation for S/N >> 1 235
10.1.8 Higher-Order Approximation for S/N > 1 238
10.1.9 Multiple-Pulse Estimates . . . . . . . 241
10.1.10 Fluctuating Targets . . . . . . . . . 242
10.1.11 “Inexact” Monopulse Processors . . . . 247
10.1.12 Closed-Loop Versus Open-Loop Operation 247
10.2 Errors Due to Clutter . . . . . . . . . . . . . 247
10.2.1 Random Error from Clutter Distributed
Across the Beam . . . . . . . . . 248
10.2.2 Number of Independent Clutter Samples 249
10.2.3 Random Error from Clutter at a Specific
Angle in the Beam . . . . . . . . 250
10.2.4 Bias Error Due to Clutter . . . . . . . 252
10.3 Dynamic Lag Error . . . . . . . . . . . . . . 252
10.3.1 Tracking-Loop Error Coefficients . . . 252
10.3.2 Pass-Course Problem . . . . . . . . . 254
10.4 Radar-Dependent Errors . . . . . . . . . . . . 256
10.4.1 Monopulse Network Effects on the
Boresight Axis . . . . . . . . . . 256
10.4.2 Boresight Axis Shift with Radar Frequency 259
10.4.3 Polarization Effects . . . . . . . . . 261
10.5 Target-Dependent Noise Errors . . . . . . . . . 263
10.5.1 Glint Error . . . . . . . . . . . . . 263
10.5.2 Scintillation Error . . . . . . . . . . 266
References . . . . . . . . . . . . . . . . . . . . . 269

Chapter 11 Multipath . . . . . . . . . . . . . . . . . . . . . 271
11.1 Flat-Earth Specular Model . . . . . . . . . . . 272
11.2 Effect on Detection . . . . . . . . . . . . . . 276
11.3 Effect on Closed-Loop Elevation Tracking . . . . . 277
11.4 Types of Multipath Remedies . . . . . . . . . . 280
11.5 Beam Pattern Design . . . . . . . . . . . . . 281
11.6 Range and Doppler Resolution . . . . . . . . . 282
11.7 Smoothing and Averaging . . . . . . . . . . . 285
11.8 “Low-E” Modes . . . . . . . . . . . . . . . 286
11.9 Offset-Null Tracking . . . . . . . . . . . . . 288