FM Airborne Passive Radar

148 Pages·2013·2.99 MB·English

FM Airborne Passive Radar
James W. A. Brown
A thesis submitted to University College London for the degree of
Doctor of Philosophy in Electronic Engineering
Department of Electronic and Electrical Engineering
University College London
April 2013
I, James W. A. Brown confirm that the work presented in this thesis is my own. Where
information has been derived from other sources, I confirm that this has been indicated in
the thesis.
James W. A. Brown
London, April 2013
1
Abstract
The airborne application of Passive Bistatic Radar (PBR) is the latest evolution of the now
established international interest in passive radar techniques. An airborne passive system
is cheaper to construct, easier to cool, lighter and requires less power than a traditional
active radar system. These properties make it ideal for installation on an Unmanned
Aerial Vehicle (UAV), especially for the next generation of Low Observable (LO) UAVs,
complementing the platforms LO design with an inherently Low Probability of Intercept
(LPI) air-to-air and air-to-ground sensing capability.
A comprehensive literature review identified a lack of practical and theoretical research
in airborne passive bistatic radar and a quantitative model was designed in order to un-
derstand the theoretical performance achievable using a hypothetical system and FM as
the illuminator of opportunity. The results demonstrated a useable surveillance volume,
assuming conservative estimates for the receiver parameters and allowed the scoping and
specification of an airborne demonstrator system.
The demonstrator system was subsequently designed and constructed and flown on
airborneexperimentstocollectdataforbothair-to-airandair-to-groundoperationanalysis.
Subsequentprocessingdemonstratedthesuccessfuldetectionofairtargetswhichcorrelated
with the actual aircraft positions as recorded by a Mode-S/ADS-B receiver. This is the
first time this has been conclusively demonstrated in the literature.
Doppler Beam Sharpening was used to create a coarse resolution image allowing the
normalised bistatic clutter RCS of the stationary surface clutter to be analysed. This is the
first time this technique has been applied to an airborne passive system and has yielded
the first quantitive values of normalised bistatic clutter RCS at VHF.
This successful demonstration of airborne passive radar techniques provides the proof
of concept and identifies the key research areas that need to be addressed in order to fully
develop this technology.
3
Acknowledgements
This work represents four five years of mental and physical investment during which I have
strayed between the lab, the Frontline and full-time employment. This would not have
been possible without the generous and patient support of Dr. Karl Woodbridge, both on
the ground and at 10,000 feet. Equally, the enthusiasm and sharp eyes of Dr. Andy Stove
and Prof. Simon Watts provided context, depth and direction, ensuring successful delivery
of this research.
The following people have provided a creative sounding board and technical advice in
the course of this work and deserve special mention: Prof. Hugh Gri�ths, Dr. Daniel
O’Hagan, Prof. Chris Baker, Prof. Paul Brennan, Dr. Kenneth Tong, Dr. Karl Erik
Olsen, Prof. Mike Inggs and Dr. David Brandwood.
I have enjoyed the experience, in no small part due to the people and personalities who
have made UCL an enjoyable, inspiring and memorable environment to work in: Dr. Matt
Ritchie, Dr. Matt Ash, Dr. Alessio Balleri, Dr. Graeme Smith, Raimund, the UCL Radar
Group and Anthony Newman.
The work would not have been possible without the funding support of Thales UK
through an EPSRC Industrial CASE Award and through the AHW Beck Memorial Schol-
arship.
1
Publications
The following papers were published as a result of this PhD research:
J. Brown, K. Woodbridge, A. Stove, and S. Watts. “Air target detection using airborne
passive bistatic radar”. Electronics Letters, 46(20):1396-1397, 30 2010.
J. Brown, K. Woodbridge, H. Gri�ths, A. Stove, and S. Watts. “Passive bistatic radar ex-
periments from an airborne platform”. IEEE Aerospace and Electronic Systems Magazine
Special Issue on PCL, 2012.
The following paper was presented at Radar 2012 and shortlisted for the best student
paper prize:
J. Brown, K. Woodbridge, A. Stove, and S. Watts. “VHF airborne passive bistatic radar
ground clutter investigation”. IET Radar Conference 2012. October 22nd to 25th 2012.
2
Contents
List of Figures 5
List of Tables 6
Nomenclature 9
1 Introduction 10
1.1 Overview and Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
1.2 Aims . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
1.3 Layout of Thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
1.4 Contributions Made by this Thesis . . . . . . . . . . . . . . . . . . . . . . . 13
2 Background 14
2.1 Bistatic Radar Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.1.1 Geometry Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.1.2 Range Relationships . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.1.3 Doppler Relationships . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.1.4 Sensitivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.1.5 Clutter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.2 Passive Bistatic Radar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.3 Literature Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
2.3.1 FM Ground Based Systems and Techniques . . . . . . . . . . . . . . 25
2.3.2 Digital Based Systems . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.3.3 Airborne Bistatic Systems and Techniques . . . . . . . . . . . . . . . 30
2.3.4 Airborne Passive Radar Research . . . . . . . . . . . . . . . . . . . . 31
2.3.5 Literature Review Summary. . . . . . . . . . . . . . . . . . . . . . . 32
2.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
3 Airborne PBR Simulation 36
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.1.1 Simulation Methodology . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.2 Line of Sight Limited Coverage . . . . . . . . . . . . . . . . . . . . . . . . . 37
3.3 Sensitivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
3.3.1 Simulation Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
3.3.2 Signal-to-Noise Ratio. . . . . . . . . . . . . . . . . . . . . . . . . . . 45
3.3.3 Signal-to-Interference Ratio . . . . . . . . . . . . . . . . . . . . . . . 48
3
3.4 Dynamic Receiver E↵ects . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
3.4.1 Clutter Doppler. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
3.4.2 Target Doppler Shift . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
3.4.3 Bistatic Multipath Analysis . . . . . . . . . . . . . . . . . . . . . . . 55
3.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
4 Hardware Development 59
4.1 System Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
4.1.1 ADC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
4.1.2 Analogue Receive Chain . . . . . . . . . . . . . . . . . . . . . . . . . 62
4.1.3 Sampling Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
4.1.4 Power Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
4.1.5 Theoretical Receiver Gain and Noise Figure . . . . . . . . . . . . . . 68
4.1.6 Operating Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
4.2 Receiver Characterisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
4.2.1 Receiver Linearity . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
4.2.2 Absolute Signal Levels . . . . . . . . . . . . . . . . . . . . . . . . . . 71
4.2.3 System Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
4.3 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
5 Airborne Experiments 78
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
5.2 Experimental Scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
5.2.1 The Airborne Platform . . . . . . . . . . . . . . . . . . . . . . . . . 78
5.2.2 FM Illuminators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
5.2.3 Air Targets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
5.3 Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
5.3.1 Airborne Experiment 1 . . . . . . . . . . . . . . . . . . . . . . . . . 88
5.3.2 Airborne Experiment 2 . . . . . . . . . . . . . . . . . . . . . . . . . 90
5.4 Initial Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
5.5 Summary and Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
6 Aircraft Detection 93
6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
6.2 Target Detection Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
6.2.1 Baseband Signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
6.2.2 DSI Mitigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
6.2.3 Matched Filtering . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
6.2.4 CFAR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
6.2.5 Target Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
6.3 Experimental Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
6.3.1 Static Receiver Experiments . . . . . . . . . . . . . . . . . . . . . . . 100
6.3.2 First Flight Experiments . . . . . . . . . . . . . . . . . . . . . . . . 104
6.3.3 Second Flight Experiment . . . . . . . . . . . . . . . . . . . . . . . . 106
6.4 Summary and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
4
7 Ground Clutter Analysis 111
7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
7.2 Doppler Beam Sharpening . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
7.2.1 Geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
7.2.2 Bistatic Stationary Clutter . . . . . . . . . . . . . . . . . . . . . . . 113
7.2.3 Cartesian Projection of Stationary Clutter . . . . . . . . . . . . . . . 114
7.3 Clutter RCS Estimation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
7.4 Bistatic Clutter Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
7.4.1 Clutter RCS Variation with Grazing Angles . . . . . . . . . . . . . . 124
7.4.2 Clutter RCS Variation with Bistatic Angle . . . . . . . . . . . . . . 124
7.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
8 Conclusions and Future Work 128
8.1 Summary of Findings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
8.2 Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
Bibliography 134
3
List of Figures
2.1 Bistatic geometry and vector definition . . . . . . . . . . . . . . . . . . . . . 15
2.2 In plane range resolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.3 Contours of constant Signal-to-Noise Ratio and constant bistatic range . . . 20
2.4 Typical ambiguity performance of a broadcast FM waveform . . . . . . . . 24
3.1 Baseline variation with receiver height . . . . . . . . . . . . . . . . . . . . . 39
3.2 Common coverage area example for typical receiver and transmitter altitudes 40
3.3 Vertical radiation pattern approximation to Wrotham FM transmitter. . . . 42
3.4 Multipath geometry for calculation of range di↵erence relative to direct path 43
3.5 ModelledSignal-to-NoiseRatioforvaryingreceiverbaselinesfromthetrans-
mitter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
3.6 Modelled Signal-to-Interference Ratio for varying baselines . . . . . . . . . . 49
3.7 Modelled Signal-to-Interference Ratio for varying baselines and additional
analogue cancellation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
3.8 Schematic for clutter Doppler analysis . . . . . . . . . . . . . . . . . . . . . 51
3.9 Bistatic Doppler scenario for stationary clutter . . . . . . . . . . . . . . . . 53
3.10 Bistatic Doppler scenario for non-stationary clutter . . . . . . . . . . . . . . 54
3.11 Geometryusedforanalysisofthemultipathonthedirectsignalforamoving
receive platform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
4.1 Receiver system block diagram . . . . . . . . . . . . . . . . . . . . . . . . . 60
4.2 Measured FM band filter S . . . . . . . . . . . . . . . . . . . . . . . . . . 63
21
4.3 Theoretical free-space received power . . . . . . . . . . . . . . . . . . . . . . 64
4.4 USB controlled oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
4.5 Measured IF filter S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
21
4.6 Sampling frequency selection . . . . . . . . . . . . . . . . . . . . . . . . . . 67
4.7 Frequency spectrum before and after sampling . . . . . . . . . . . . . . . . 68
4.8 Channel circuit diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
4.9 LabView control GUI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
4.10 1 dB compression point measurements . . . . . . . . . . . . . . . . . . . . . 71
4.11 Third order intercept point extrapolation for the reference channel . . . . . 72
4.12 Pre-IF filter noise figure measurement . . . . . . . . . . . . . . . . . . . . . 73
4.13 System noise figure measurement . . . . . . . . . . . . . . . . . . . . . . . . 74
4.14 Completed receiver - under the lid . . . . . . . . . . . . . . . . . . . . . . . 75
4.15 Completed receiver - front aspect . . . . . . . . . . . . . . . . . . . . . . . . 75
4.16 Completed receiver - rear aspect . . . . . . . . . . . . . . . . . . . . . . . . 77
4
LIST OF FIGURES LIST OF FIGURES
5.1 PA 28-181 G-BMIW airborne. . . . . . . . . . . . . . . . . . . . . . . . . . . 79
5.2 PA 28-181 dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
5.3 Air chart of airborne experiments . . . . . . . . . . . . . . . . . . . . . . . . 80
5.4 Local and national BBC FM transmitter locations . . . . . . . . . . . . . . 84
5.5 Air truth flight paths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
5.6 Air truth altitude distribution . . . . . . . . . . . . . . . . . . . . . . . . . . 87
5.7 Air truth airspeed distribution . . . . . . . . . . . . . . . . . . . . . . . . . 88
5.8 System installation in the PA 28-181 . . . . . . . . . . . . . . . . . . . . . . 89
5.9 Flightpath for the first airborne experiment . . . . . . . . . . . . . . . . . . 89
5.10 Flightpath for the second airborne experiment . . . . . . . . . . . . . . . . . 90
5.11 Matlab processing block diagram . . . . . . . . . . . . . . . . . . . . . . . . 92
6.1 Target detection processing overview . . . . . . . . . . . . . . . . . . . . . . 94
6.2 Direct signal suppression filtering of surveillance channel . . . . . . . . . . . 96
6.3 CFAR window construction . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
6.4 Example ARD for the static system . . . . . . . . . . . . . . . . . . . . . . 101
6.5 Example ARD for the static system . . . . . . . . . . . . . . . . . . . . . . 101
6.6 Cumulative detection surface for stationary receiver . . . . . . . . . . . . . 102
6.7 Cumulative detection surface for stationary receiver with air truth . . . . . 103
6.8 Aggregated detections in range-Doppler plane for the second experiment . . 104
6.9 First airborne target detections in Cartesian plane . . . . . . . . . . . . . . 106
6.10 Raw detections from Wrotham transmitter . . . . . . . . . . . . . . . . . . 107
6.11 Raw detections from Oxford transmitter . . . . . . . . . . . . . . . . . . . . 108
6.12 Second airborne experimental results in range-Doppler plane . . . . . . . . 109
7.1 Geometry for Doppler Beam Sharpening derivation . . . . . . . . . . . . . . 112
7.2 Bistatic image formation starting product . . . . . . . . . . . . . . . . . . . 115
7.3 Cross-range beam width variation across a scene . . . . . . . . . . . . . . . 116
7.4 Doppler beam sharpened surface . . . . . . . . . . . . . . . . . . . . . . . . 117
7.5 Clutter cell area estimation for a typical scenario . . . . . . . . . . . . . . . 118
7.6 Doppler beam sharpened PPI image example . . . . . . . . . . . . . . . . . 120
7.7 Estimated transmitter and receiver Line-of-Sight for the second experiment 121
7.8 Surface clutter-to-noise ratio Doppler Beam Sharpened image . . . . . . . . 123
7.9 Estimated median clutter power variation with bistatic angle . . . . . . . . 125
7.10 Estimated median normalised RCS variation with bistatic angle . . . . . . . 126
5