Table Of ContentP r i n c i p l es of s p a c e - t i me
a d a p t i ve p r o c e s s i ng
R i c h a rd K l e mm
The Institution of Electrical Engineers
Published by: The Institution of Electrical Engineers, London,
United Kingdom
©2002: The Institution of Electrical Engineers
This publication is copyright under the Berne Convention and the
Universal Copyright Convention. All rights reserved. Apart from any fair
dealing for the purposes of research or private study, or criticism or
review, as permitted under the Copyright, Designs and Patents Act, 1988,
this publication may be reproduced, stored or transmitted, in any forms or
by any means, only with the prior permission in writing of the publishers,
or in the case of reprographic reproduction in accordance with the terms
of licences issued by the Copyright Licensing Agency. Inquiries
concerning reproduction outside those terms should be sent to the
publishers at the undermentioned address:
The Institution of Electrical Engineers,
Michael Faraday House,
Six Hills Way, Stevenage,
Herts. SG1 2AY, United Kingdom
While the author and the publishers believe that the information and
guidance given in this work is correct, all parties must rely upon their own
skill and judgment when making use of it. Neither the author nor the
publishers assume any liability to anyone for any loss or damage caused
by any error or omission in the work, whether such error or omission is
the result of negligence or any other cause. Any and all such liability is
disclaimed.
The moral right of the author to be identified as author of this work has
been asserted by him/her in accordance with the Copyright, Designs and
Patents Act 1988.
British Library Cataloguing in Publication Data
Klemm, Richard
Principles of space-time adaptive processing.
(Radar, sonar, navigation and avionics series; no. 12)
1. Moving target indicator radar
I. Title II. Institution of Electrical Engineers
621.3'84S
ISBN 0 85296 172 3
Printed in England by MPG Books Ltd., Bodmin, Cornwall
To my wife Erika
who likes living beings much better than technical matters
Biography
Richard Klemm was born in 1940 in Berlin, Germany. He received his Dipl.-Ing. and
Dr.-Ing. degrees in communications from the Technical University of Berlin in 1968
and 1974, respectively.
From 1968 to 1976 he was with FGAN-FFM (Research Institute for Radio and
Mathematics, a branch of the German Defence Research Establishment) at Wachtberg,
Germany. His main field of activity has been adaptive clutter and jammer suppression
for radar.
From 1977 to 1980 he was with SACLANT ASW Research Centre, La Spezia,
Italy, where he conducted studies on spatial signal processing for active and passive
sonar, with emphasis on matched field processing for shallow water applications.
Since 1980 he has again been with FGAN-FFM where he has been working on
aspects of anti-jamming and detection of moving targets for moving sensor platforms.
He has published numerous articles on various aspects of radar and sonar signal
processing, with particular emphasis on space-time adaptive processing. He is a
permanent reviewer of renowned journals such as IEEE Transactions on Aerospace
Systems and IEE Proc. Radar, Sonar and Navigation. Richard Klemm has given
several invited seminars on STAP in different countries.
Dr. Klemm has been a member of the Sensor and Propagation Panel of AGARD
(nowadays the RTO-SET panel) and is a member of Commission C (Signals and
Systems) of URSI. He chaired several AGARD and RTO symposia and was chairman
of the AGARD Avionics Panel. He initialised and chaired the first European
Conference on Synthetic Aperture Radar (EUSAR'96), March 1996, in Konigswinter,
Germany.
In his spare time Richard Klemm is a passionate classical pianist. Under the
headline Science and Music he likes to combine his technical and musical sides by
giving piano recitals at technical conferences. Dr. Klemm is married and has three
children and four grandchildren.
Preface to the first edition
Space-time processing has become very popular in the past few years. In particular
space-time adaptive processing (STAP) with application to airborne MTI radar has
become a key topic of international radar conferences. Although mainly used for
airborne MTI (moving target indication) radar other applications are possible.
Air- and spaceborne radar plays an important role for civilian and military
use. There are numerous applications such as earth observation, surveillance,
reconnaissance and others. Among a large number of facets of air- and spaceborne
radar the capability of moving target detection plays an important role. This book
focuses on a specific part of air- and spaceborne MTI radar: the suppression of clutter
returns.
Look at the following simple formula
It shows the dependence of the clutter Doppler frequency on the angle between an
individual clutter scatterer and the flight direction. It seems hard to believe that one
can write a thick book on such a simple matter. But it's true - this book deals with the
consequences arising from this little formula.
The directional dependence of the clutter Doppler frequency as given by the above
formula leads to the concept of adaptive space-time clutter filtering which is expanded
in some detail. The design of suboptimum processors promising near optimum
performance at low cost, reduced computing time, weight, energy consumption, etc.,
in other words, enabling real-time operation on small radar platforms, is the main goal
of this book. The basis for space-time signal processing is a multichannel phased array
antenna which provides spatial sampling of the backscattered echo field.
Since I started this work the radar world has changed considerably. While 15
years ago phased array antennas were still considered to be futuristic because the
technology was still in an early stage they are nowadays state of the art. In the
same timeframe dramatic progress in digital technology took place which led to
powerful programmable signal processors, including parallel processing architectures.
Moreover, a lot of theoretical work has been devoted to the development of new array
processing techniques and algorithms. For a large number of applications the next
generation of radar will include active multichannel phased array antennas. Such radar
offers high flexibility, reliability, and, in conjunction with appropriate array processors,
the potential of multichannel signal processing. In other words, the technology for
real-time airborne MTI is there.
When I started working on airborne MTI there was not much material available in
the open literature. The first publications date back to the 1970s (papers on DPCA even
earlier). The first paper on adaptive clutter cancellation for airborne radar is the one
by BRENNAN et al. [53]. In the meantime research on space-time adaptive processing,
nowadays widely known by its acronym 'STAP', has grown tremendously. There are
activities all over the world, especially in the USA and China.
A lot of the existing literature is concerned with the problem of suboptimum
processor design. 'Suboptimum' means that the clutter rejection performance should
be as close as possible to the optimum processor, however at much less cost and
complexity. It was not my intention to summarise and compare all the various technical
solutions proposed in the literature - this would exceed the limits of such book, and
at the end the reader is still left with the problem of selecting his favourite solution. I
tried instead to present as much insight as possible into the problems in order to help
the reader understand the phenomena associated with adaptive space-time processing.
I hope the reader will appreciate this.
Besides taking a lot of literature by other authors into consideration I tried to
summarise mainly the insights and results of about 15 years of my own research in
the field of air- and spaceborne MTI radar. In that sense this book certainly does not
cover the whole STAP area. However, there are nowadays so many proposals for STAP
processor architectures in the literature that it is hardly possible to describe all of them
or even to compare them. By following the line of my own research and communicating
the insights I obtained I hope to contribute to a better understanding of the associated
problems. Maybe this makes this book even more valuable than presenting an overview
of the existing literature.
The text includes in essence a selection of numerical results obatined for linear
antenna arrays. These results are based on a specific parameter constellation which is
given in Chapter 2. Consequently, the results are not exhaustive and are not meant to
be. It is certainly not possible to address all potential combinations of radar parameters.
Moreover, linear arrays are normally not used in radar applications. However, they are
relatively easy to handle numerically and exhibit some fundamental properties which
form a good basis for understanding the various effects. In that sense the examples
presented are meant to be a guideline for the radar designer on how to proceed finding
the solution for his actual problem.
I should mention that all beforementioned results have been obtained by
calculations based on simple signal and clutter models. I agree that beyond the
information presented to the reader many open questions will remain, which are in
part related to the 'real world', i.e., the limited validity of computer models. Such
limitations are mostly caused by differences between an ideal and a real radar sensor
and also by the statistical behaviour of the target and clutter environment. Some
of the results obtained may turn out to be too optimistic and need experimental
verification. Nevertheless, I am convinced that in general such model studies are very
useful to understand the mechanisms behind the observed phenomena, and can be used
to pre-select promising practical solutions. Following this line some of the results
presented here have contributed to international projects such as EUCLID, SWORD
and AMSAR.
It is assumed that the reader has some basic knowledge of pulse Doppler radar,
including the radar range equation, conventional MTI techniques, antenna arrays,
signal and array processing, and is familiar with some fundamentals of statistical
detection theory and complex matrix algebra.
My book is intended to be a systematic introduction to airborne MTI system design.
It is organised in the following way: First a brief overview of potential array and signal
processing techniques and the signal and clutter models used is presented (Chapters 1-
3). Some basic properties of airborne clutter are summarised. Secondly the discussion
of space-time adaptive clutter filters starts with optimum processing as given by
array processing theory (Chapter 4). In this part the basic behaviour of space-time
clutter suppression techniques is discussed, keeping in mind that the implementation
of such techniques in practical systems is not realistic. In the sequel (Chapters 5-7)
suboptimum processing techniques based on linear arrays will be presented which are
more and more adapted to practical requirements, including aspects of on-board and
real-time processing. The techniques discussed in these chapters are based on signal
processing in a vector subspace. Such techniques have been frequently referred to as
partially adaptive.
Chapter 8 deals with non-linear antenna configurations. Circular planar arrays
with realistic numbers of sensors are discussed. Chapter 9 deals with space-frequency
techniques. In Chapter 10 aspects of clutter suppression under jamming conditions are
considered. In particular the question is raised whether clutter and jamming should be
filtered simultaneously or by cascaded anti-jamming/anti-clutter filters. In Chapter 11
two applications for space-time processing in SAR or ISAR are presented. Although
the applications are quite different in nature it is shown that they are based on the same
mathematical background. In Chapter 12 finally miscellaneous aspects (array errors,
aspects of implementation, computational complexity of processing techniques, etc.)
and issues of space-time filtering are presented. Each of the twelve chapters concludes
with a short summary highlighting the major findings of the individual chapter. The
book concludes with a listing of more than 350 references which I collected up to the
last moment before delivering the manuscript. By doing so I intended to include recent
literature as much as possible.
Although this book contains a lot of numerical results it is not meant to be a
handbook from which the user can extract technical data. It is merely intended to
present the principles of space-time processing and to show the radar designer how to
find his personal solution. In that sense I also anticipate that the book may serve as a
background document for courses at universities or other technical institutions. I hope
sincerely that the reader will find this book useful and will be stimulated to do his own
research in this magic area.
The motivation to summarise all the work done on air- and spaceborne MTI radar
in the past 15 years originates from several seminars which I gave on invitation by
Ericsson, Sweden, and by three universities in China. The interest in this field is
currently very strong so that I felt I should communicate as many details as I know
to the public. There is at least one item which I have contributed to the world of space-
time adaptive processing: to my knowledge all authors working in this field denote the
number of antenna elements by TV and the number of echo pulses by M as I did in my
paper of 1983 [238]. I will keep with that tradition.
Acknowledgements. I would like to thank Dr. habil. J. Grosche, director of
FGAN-FFM, for his generous and enthousiastic support of this work.
Dr. Wirth, head of the Electronics Department of FFM, suggested that I start
research into adaptive airborne MTI as early as 1980. His continuous encouragement
and numerous fruitful discussions and suggestions improved my understanding of the
problems considerably. Dr. Wirth's co-operation is gratefully acknowledged.
I would like to thank my colleagues Dr. U. Nickel and Dr. J. Ender for contributing
a number of valuable ideas. Furthermore, I owe thanks to O. Kreyenkamp for numerous
discussions and helpful suggestions. I thank Dr. W.-D. Wirth and O. Kreyenkamp for
their help in proofreading the manuscript.
In particular I would like to thank Mrs. G. Gniss. She carried out all the numerical
evaluation and listened to my explanations of various physical matters with patience.
Thus she helped me to understand at lot of the phenomena just by listening. It would
have been impossible to write such a book without her continuous and ambitious
assistance. More than 25 years of excellent co-operation with Mrs. Gniss are gratefully
acknowledged.
I am indebted to H. Wolff of the German Ministry of Defence for his continuous
support of my research activities over many years which have now been summarised
in this book.
I feel obliged to thank Osten Erikmats of Ericsson, Molndal, Sweden, who invited
me to give a seminar at the radar division of his company. This invitation encouraged
me to compile all my material on space-time processing which in turn stimulated the
idea of summarising my work in a book.
I owe many thanks to the Chinese Professors Peng Yingning (Beijing), Wu Shunjun
and Bao Zheng (Xi'an), and Huang Shun-Ji (Chengdu), for offering me the opportunity
to give lectures on space-time adaptive processing at their universities. The discussions
with them as well as with their colleagues and students were of high value for this
undertaking.
Writing a book means first of all learning a great deal. I wish to thank all
those authors who contributed to the field of space-time adaptive processing with
publications and contributions to international conferences. I apologize for any
publication I may have overlooked.
The excellent co-operation with the publisher, in particular the commissioning
editor, J. Simpson, should be emphasised. I feel indebted to Prof. H. Griffiths, editor
of Proc. IEE on Radar, Sonar and Navigation, for his encouraging support. I owe
many thanks to the editors of the IEE radar series, Prof. E. D. R. Shearman and P.
Bradsell, and also C. Wigmore and Dr. N. Steward of Siemens-Plessey for reviewing
the manuscript and giving many helpful suggestions. In particular I am grateful to
Dr. John Mather of DERA for carefully reviewing the manuscript. His numerous
comments and suggestions improved considerably the quality of this book.
R. Klemm, Wachtberg, 1997
Preface to the second edition
The worldwide interest in space-time adaptive processing continues to be strong. The
little Doppler formula on which all STAP activities (and, moreover, SAR) are based
(see the preface to the first edition) has not lost its magic fascination. No future military
air- or spaceborne observation radars will be designed without the capability of slow
moving target detection. We felt that a second edition of this book would be useful as
an introduction to this still fascinating field. In the meantime many new results and
additional insight into the various problems have been gained.
The second edition has been enlarged by almost 30%. In detail the following major
changes have been made:
• A few errata have been corrected. I am grateful for all the advice I received from
several readers.
• A new Chapter 10 has been added which deals with the effect of radar
ambiguities in range and Doppler.
• The new Chapter 12 gives an introduction to space-time adaptive clutter
suppression for bistatic radar configurations
• The new Chapter 14 addresses the problem of estimating the target azimuth and
velocity in the presence of Doppler coloured clutter. The Cramer-Rao bounds
for various processor architectures are treated as well as the impact of radar
parameters on the estimation accuracy. The performance of adaptive monopulse
is studied.
• The degradation of the performance of the space-time FIR filter by temporal
decorrelation due to internal clutter motion has been added (Chapter 7).
• The effect of range walk has been incorporated in Chapters 2, 3, 4 and 7.
• The effect of Doppler spread in large range bins has been analysed (Chapters 2
and 4)
• Some discussion of the range dependence of the clutter Doppler and related
compensation techniques has been added to Chapter 10.
• The use of the space-time FIR filter with staggered PRI has been added to
Chapter 10.
• The bibliography has been updated by including over 210 recent publications.
I hope that the reader will appreciate this effort and that the second edition will be
received by the international radar community in the same way as the first one.
Acknowledgements. I would like to thank Prof. Dr. K. Krucker, Director of
FGAN-FHR, for his support of this work. Dr. J. Ender, head of FGAN-FHR/EL,
contributed numerous knowledgeable suggestions which improved my insight into
certain problems. I am indebted to my colleague Dr. U. Nickel who contributed a
number of valuable ideas. As in the first edition Mrs. G. Gniss performed the numerical
evaluation. I am grateful for her enthusiastic assistance in completing this work.
I feel obliged to thank Prof. G. Galati (Italy), R. T. Hill, Dr. E. J. Ferraro
(USA), Dr. P. Bhartia (Canada), G. P. Quek (Singapore), Dr. E. Velten, Prof. K.
Krucker (Germany), Dr. W. Klembowski (Poland), Prof. B. Kutuza (Russia), and
Dr. S. Kent (Turkey) for offering me the opportunity to give seminars on space-time
adaptive processing in their organisations and to discuss details with their colleagues
and students.
I am particularly grateful to to P. Richardson who thoroughly reviewed the
entire manuscript. He made a number of valuable suggestions which have all been
incorporated in the text. Finally, the excellent cooperation with the publisher, especially
the commissioning editor, Dr. R. Harwood, and the production editor, Diana Levy, is
greatly appreciated.
R. Klemm, Wachtberg, 2001
