Radar techniques using array antennas

491 Pages·2001·18.69 MB·English

by  Wulf-Dieter Wirth

R a d ar t e c h n i q u es
u s i ng a r r ay a n t e n n as
W u l f - D i e t er W i r th
The Institution of Electrical Engineers
Published by: The Institution of Electrical Engineers, London,
United Kingdom
© 2001: The Institution of Electrical Engineers
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British Library Cataloguing in Publication Data
Radar techniques using array antennas.
(Radar, sonar, navigation and avionics series; no. 10)
1. Radar 2. Antenna arrays
I. Wirth, W.
621.3' 8483
ISBN 0 85296 798 5
Typeset by Newgen Imaging Systems, India
Printed in England by Antony Rowe Ltd., Chippenham
To Christiane
Preface
The intention of this book is to give the reader an introduction into the area of modern
radar techniques based on active array antennas, either for use in development and
research or as a decision and planning aid for the authorities within government
or industry. In particular, many new possibilities are discussed which should find
consideration for future radar systems. I have assumed the general basics of radar
technology to be familiar to the reader; introductory literature is widely available.
I have tried to present the techniques, procedures and concepts, which can mostly
be derived from signal-theoretical views and which are described with approaches
and equations, from an engineering point of view, with a minimum of mathematical
treatment. As far as is possible, a descriptive and functional explanation is given for
each procedure.
Despite its already long history, radar technology will continue to receive attention
for many years to come. The importance of radar results from its ability to provide
reconnaissance, especially target detection, location and imaging, in all weather con-
ditions and from short to long ranges. This ability results from the relatively small
propagation attenuation of the electromagnetic waves with wavelengths in the cen-
timetre to metre range. These wavelengths also permit sufficient location accuracies
and resolutions with reasonable antenna dimensions. Radar works actively, illuminat-
ing the scene to be observed with its own transmitter. From this results its ability to
measure target range and its independence from daylight, in contrast to visual optics.
One can thus expect future lively interesting and importance for radar technology.
This statement is among other aspects confirmed by a well-established regular series
of international radar conferences organised by respected and famous professional
institutions such as IEE (UK), IEEE (USA), DGON/ITG (GE), SEE (F).
The idea of writing this book was first developed by contributions and the sci-
entific coordination of the training course 'Future radar systems' of the Carl Cranz
society in Germany. Here in this book the material is presented in much more detail
than is possible in a short course. Beyond this, the book is essentially based on experi-
ences, implementations and new concepts which my colleagues and I have developed
and collected in the course of more than 30 years of scientific work in the radar
field at the Forschungsinstitut fur Funk und Mathematik (FFM, which translates
into Research Institute for Radio Sensors and Mathematics) of the Forschungs-
Gesellschaft fiir Angewandte Naturwissenschaften (FGAN, which translates into
Research Association for Applied Natural Sciences).
In the introduction a general representation of the substantial future requirements
for radar systems is given. Afterwards, the future importance of multifunction sys-
tems on the basis of electronically-steered array antennas is discussed. In the chapters
2, 3 and 4 there follows a short introduction into representation of signals, into the
statistical signal theory and into the substantial characteristics, architectures and rela-
tionships of array antennas. These array antennas may be of linear, planar, cylindrical
or volume type. These chapters shall be used as a basis for the following chap-
ters. In chapter 5 the receiver beamforming is discussed. Chapter 6 deals with the
time-discrete signal sampling and derivation of the orthogonal signal components.
Chapter 7 is dedicated to pulse compression with the use of polyphase codes, with
special compression procedures for sidelobe reduction and an improvement of the
range resolution. In chapter 8 we treat problems and possibilities for target detection
from signal series, i.e. incoherent and coherent integration, Doppler filtering, adap-
tive clutter suppression and the coherent processing of very long pulse series with
a special test function. Chapter 9 presents sequential detection for radar application
and its advantages, together with a solution for the problem of simultaneously testing
multiple range bins.
Chapters 10 to 15 are dedicated to concepts, procedures and applications of array
signal processing. In chapters 10, 11 and 12 adaptive jammer suppression, correction
of monopulse under jamming conditions and angular superresolution are discussed. In
chapters 13 and 14 the additional possibilities and special problems of radar on flying
platforms are presented, especially with respect to the detection of slowly moving tar-
gets, that is space-time adaptive processing (STAP) procedures and synthetic aperture
radar (SAR) with moving target indication (MTI) and target imaging. In chapters 15
the principles of inverse synthetic aperture radar (ISAR) are introduced as a way
of generating radar images for detected moving targets. In chapter 16 fluctuation
and spectral target characteristics, especially by jet engine modulation, are described.
Both of these last chapters demonstrate the contributions to target classification which
can be achieved with a multifunction radar.
In chapter 17 a survey of the experimental phased array radar system ELRA
which has been developed at FFM is given. In chapter 18 follows the description of a
special system concept with omnidirectional or floodlight transmission and a multi-
beam receiving system for radar operation with protection against antiradar missiles
(ARMs). An additional application of this concept is the detection and classification of
hovering helicopters. The corresponding experimental system OLPI following these
concept ideas is described. Finally, in chapter 19 some remarks are made on system
parameter relations and their choice for a multifunction radar system which is based
on a phased-array antenna.
I would like to thank all my colleagues at the department EL (electronics) of
FGAN-FFM for my long, very fruitful and enjoyable time as department head.
Especially I am grateful for many years of scientific cooperation, with numerous
stimulating discussions, with W. Buhring, J. Ender, I. Groger, E. Hanle, R. Klemm,
U. Nickel, W. Sander, K. V. Schlachta and H. Wilden. Their contributions to our work
are also documented by the references at the end of each chapter.
I would also like to thank Dr. Robin Mellors-Bourne, Diana Levy and Dr. Roland
Harwood who, as the Book Publishing Department at the IEE, provided much support.
The excellent co-operation that I received is very much appreciated. I also owe thanks
to the editors of the IEE radar series, Professor E. D. R. Shearman and Professor
P. Bradsell, and to the anonymous reviewers for their numerous corrections, creative
comments and suggestions.
Finally, I thank the director of the FFM Dr. Jiirgen Grosche and the head of
the responsible department section within the German Ministry of Defence (BMVg)
Hartmuth Wolff for the promotion of my work over many years in the exciting area
of modern radar techniques and for the encouragement to write this book.
Wulf-Dieter Wirth
October 2000
Contents
Preface ................................................................................ xv
1. Introduction ................................................................. 1
2. Signal Representation and Mathematical
Tools ............................................................................ 5
2.1 Vectors, Matrices ........................................................... 5
2.2 Computing with Matrices ............................................... 6
2.2.1 Addition and Subtraction .............................. 6
2.2.2 Multiplication ................................................ 7
2.2.3 Identity Matrix .............................................. 8
2.2.4 Inverse Matrix .............................................. 9
2.2.5 Eigenvalue Decomposition ........................... 9
2.2.6 QR Decomposition ....................................... 10
2.3 Fourier Transform .......................................................... 10
2.3.1 Fast Fourier Transform, FFT ........................ 12
2.4 Filter in the Frequency and Time Domain ..................... 12
2.5 Correlation ..................................................................... 15
2.6 Wiener Khintchine Theorem .......................................... 16
2.7 References .................................................................... 17
3. Statistical Signal Theory ............................................ 19
3.1 The General Tasks of Signal Processing ...................... 19
3.2 Introduction to Basics of Statistics ................................. 20
3.2.1 Probabilities for Discrete Random
Variables ...................................................... 21

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viii Contents
3.2.2 Continuous Random Variables ..................... 23
3.2.3 Functions of Random Variables ................... 26
3.2.4 Statistical Averages ..................................... 30
3.2.5 Correlation ................................................... 32
3.2.6 Gaussian Density Function .......................... 32
3.2.7 Correlated Gaussian Variables .................... 33
3.2.8 Complex Gaussian Variables ....................... 34
3.3 Likelihood-ratio Test ...................................................... 35
3.4 Parameter Estimation .................................................... 40
3.4.1 Variance of the Estimate and
Cramér-Rao Limit ........................................ 41
3.5 Estimation of a Signal .................................................... 45
3.5.1 Maximum-likelihood Estimation .................... 45
3.5.2 Signal Estimation with Least-mean-
square Error ................................................. 46
3.5.3 Interference Suppression by the
Inverse Covariance ...................................... 47
3.5.4 Improvement of Signal-to-noise-and-
interference Ratio (SNIR) ............................. 49
3.6 Summary ....................................................................... 49
3.7 References .................................................................... 50
4. Array Antennas ........................................................... 51
4.1 Array Factor ................................................................... 52
4.2 Array Parameters .......................................................... 57
4.2.1 Half-power Beamwidth ................................. 58
4.2.2 Bandwidth Limitation with Phase
Steering ....................................................... 58
4.2.3 Antenna Element Spacing Without
Grating Lobes .............................................. 60

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Contents ix
4.2.4 Gain of Regularly Spaced Planar
Arrays with d = λ/2 ....................................... 61
4.2.5 Reduction of Sidelobes by Tapering ............ 61
4.3 Circular Array ................................................................. 64
4.4 Phase and Amplitude Errors ......................................... 65
4.5 Architectures of Passive and Active Array
Antennas ........................................................................ 71
4.5.1 Comparison of Efficiency for Active and
Passive Arrays ............................................. 75
4.5.2 Radar Equation for Active Arrays ................. 75
4.6 Concepts for an Extended Field of View ....................... 76
4.6.1 Volume Array for Complete Azimuth
Coverage ..................................................... 77
4.7 Monitoring of Phased-array Antennas .......................... 79
4.7.1 Antenna Measurement ................................. 80
4.7.2 Transmit/Receive Module (TRM)
Monitoring .................................................... 81
4.8 Appendix: Taylor and Bayliss Weighting ....................... 83
4.9 References .................................................................... 85
5. Beamforming ............................................................... 87
5.1 Single Receiving Beam ................................................. 89
5.1.1 RF Beamforming .......................................... 89
5.1.2 Subarrays and Partial Digital
Beamforming ............................................... 89
5.1.3 Dynamic Range Requirements .................... 91
5.1.4 Subarray Configuration for Digital Sum
and Difference Beamforming ....................... 92
5.1.5 Correction of Antenna Failures .................... 96
5.1.6 Digital Beamforming at Element Level ......... 97
5.2 Broadband Beamforming .............................................. 97

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x Contents
5.3 Multiple Beams .............................................................. 101
5.3.1 RF Multiple Beamforming ............................. 102
5.3.2 RF Multiple Beamforming Using
Subarrays .................................................... 103
5.3.3 IF Multiple Beamforming by a Resistive
Network ....................................................... 104
5.3.4 Baseband Multiple Beamforming ................. 104
5.3.5 Time-multiplex Beamforming for
Arbitrary Directions ...................................... 104
5.3.6 Digital Multiple Beamforming Using
Subarrays .................................................... 104
5.3.7 Multiple Beam Cluster for Target
Search ......................................................... 106
5.4 Deterministic Spatial Filtering ........................................ 107
5.5 References .................................................................... 109
6. Sampling and Digitisation of Signals ........................ 111
6.1 Analytical Signal ............................................................ 111
6.2 Sampling and Interpolation ............................................ 114
6.3 Extraction of the Components I and Q in Digital
Format ............................................................................ 116
6.4 Third-order Intercept Point (TOI) and Dynamic
Range ............................................................................ 121
6.5 References .................................................................... 123
7. Pulse Compression with Polyphase Codes ............. 125
7.1 Introduction .................................................................... 125
7.2 Requirements and Basic Structure for Pulse
Compression .................................................................. 126
7.3 Binary Phase Codes ...................................................... 127
7.4 Polyphase Code as an Approximation of Linear
Frequency Modulation ................................................... 128

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