Contents Abstract v Declaration vii Acknowledgements ix List of Figures xi List of Tables xix Abbreviations xxi Symbols xxv Publications xxix 1 Introduction 1 1.1 Problem Description .................................................................................................... 1 1.2 Outline of Thesis and Main Contributions .................................................................. 4 2 GPS Bistatic Radar Background for Target Detection 7 2.1 Introduction ................................................................................................................. 7 2.2 Background of Passive Bistatic Radar ........................................................................ 7 2.3 PBRs Performance Comparison ................................................................................ 10 2.4 Background of GPS ................................................................................................... 11 2.4.1 GPS Signal Detection Techniques .................................................................. 13 2.5 GPS Bistatic Radar Detection Applications .............................................................. 18 2.6 GPS Signal Air Target Detection for Passive Bistatic Radar ................................... 20 2.6.1 Coherent Integration ....................................................................................... 21 2.6.2 Non-coherent Integration ................................................................................ 22 2.6.3 Radar Cross-section ........................................................................................ 23 i ii CONTENTS 2.6.4 Phased-array Technique .................................................................................. 24 2.6.5 MIMO Radar Technique ................................................................................. 25 2.7 Proposed Research .................................................................................................... 27 2.7.1 Coherent Integration ....................................................................................... 27 2.7.2 Phased-array Technique .................................................................................. 29 2.7.3 MIMO Radar Technique ................................................................................. 30 2.8 Conclusion ................................................................................................................. 30 3 Feasibility of Target Detection using Phased-array Technique 33 3.1 Introduction ............................................................................................................... 33 3.2 Estimation of Parameters for GPS Bistatic Radar ..................................................... 34 3.2.1 Power Measurement of Target Scattering ...................................................... 34 3.3 Background of Phased-array Technique ................................................................... 39 3.3.1 Phased-array Receiver for PBR ...................................................................... 40 3.3.2 Null-Steering ................................................................................................... 43 3.3.3 Discussion of Phased-array Technique for GPS Bistatic Radar ..................... 43 3.4 Antenna Array Calibration Technique ...................................................................... 45 3.4.1 Background ..................................................................................................... 45 3.4.2 Phase Error Calibration for GPS Bistatic Radar ............................................. 47 3.4.3 Attitude Calibration of Receiving Array for GPS Bistatic Radar ................... 49 3.5 Target Verification and Identification Process.......................................................... 50 3.5.1 Target Detection Modelling ............................................................................ 52 3.5.2 Simulation Example of Target Detection ....................................................... 54 3.5.3 Target Parameter Estimation .......................................................................... 60 3.5.4 Simulation Example of Target Parameters Estimation ................................... 64 3.6 Conclusion ................................................................................................................. 71 4 GPS Bistatic Radar using MIMO Technique 75 4.1 Introduction ............................................................................................................... 75 4.2 MIMO Radar Target Detection Model for GPS Bistatic Radar ................................ 76 4.3 Performance of MIMO Technique for GPS Bistatic Radar ...................................... 79 CONTENTS iii 4.3.1 Target Detection Performance ........................................................................ 80 4.3.2 Target Location Estimation Accuracy ............................................................ 83 4.3.3 Computational Complexity ............................................................................. 85 4.4 Simulation of Target Detection Results for GPS MIMO Radar ............................... 85 4.4.1 Target Detection (SISO vs. MISO) ................................................................ 86 4.4.2 Target Detection (MISO vs. MIMO) .............................................................. 93 4.4.3 Detection for Multiple Targets (SISO vs MISO vs MIMO)........................... 98 4.4.4 Target Tracking for GPS MISO/MIMO Radar ............................................ 101 4.5 Conclusion ............................................................................................................... 108 5 Experimental Target Detection Performance for GPS Bistatic Radar 113 5.1 Introduction ............................................................................................................. 113 5.2 Experimental Receiver for Air Search GPS Bistatic Radar .................................... 116 5.2.1 Description of Receiver’s Design ................................................................. 116 5.2.2 Receiver Performance Benchmark ............................................................... 121 5.3 Direct-path Signal Acquisition ................................................................................ 123 5.4 Experimental Antenna Array Calibration Results ................................................... 130 5.4.1 Antenna Array Deployment .......................................................................... 130 5.4.2 Calibration Process and Outcome ................................................................. 130 5.4.3 Verification of Calibration Results ............................................................... 132 5.5 Direct-path Signal Interference Cancellation Technique ........................................ 137 5.5.1 Background ................................................................................................... 137 5.5.2 Simulation Examples of DSI cancellation technique ................................... 140 5.5.3 Experimental results using DSI cancellation technique ............................... 143 5.6 Experimental Results from Air Target Detection ................................................... 145 5.6.1 Experiment Scenario for Target Detection ................................................... 145 5.6.2 Phased-array Detection Technique ............................................................... 148 5.6.3 MISO Radar Detection Technique ............................................................... 160 5.7 Conclusion ............................................................................................................... 165 6 Conclusion 167 iv CONTENTS 6.1 Summary and Contributions.................................................................................... 167 6.2 Further Recommendations ...................................................................................... 170 References 171 Abstract GPS passive bistatic radar uses signals transmitted by navigation satellites to perform target detection. This research aims to develop a ground-based receiver that detects the reflected GPS signals from air targets. The main challenge for GPS bistatic radar is the difficulty in detecting the extremely weak power GPS signal reflections from a target since GPS satellites are located at very high altitudes and transmit signals at relatively low power levels. The research in this thesis investigates the minimum power of the reflected GPS signal that can be reliably detected by applying several techniques for enhancing the receiver detection performance. The proposed techniques for GPS bistatic radar target detection model include: using a large scale antenna array at the receiver, applying long coherent integration times for the captured data and non-coherently summing the power returns of targets from multiple satellites or receivers. This detection model requires the radar system to incorporate the signal information from a large number of receiving channels and non-cooperative transmitters to perform air target detection. This research also incorporates additional techniques at the pre-detection stage that are essential for the target detection model. Among these techniques include: direct-path GPS signals acquisition that obtains the Doppler frequency component and C/A code pattern from each satellite, array calibration that realigns the inter-element phase errors and orientation of phased-array receiver using the GPS system, and direct-path signal interference cancellation. The GPS bistatic radar target detection performance was initially investigated using the results produced by computer simulations. Then, a prototype phased-array GPS bistatic radar receiver was built to capture target reflections from an aircraft and investigate the detection performance of the system experimentally. The system was able to successfully detect and locate the position of a nearby aircraft, which demonstrates that the techniques introduced for GPS bistatic radar in this thesis do work in practice. The experimental results also provide a v vi Abstract benchmark that can be used to estimate the scale of the receiver required for detecting objects at a greater distance. Declaration I certify that this work contains no material which has been accepted for the award of any other degree or diploma in my name, in any university or other tertiary institution and, to the best of my knowledge and belief, contains no material previously published or written by another person, except where due reference has been made in the text. In addition, I certify that no part of this work will, in the future, be used in a submission in my name, for any other degree or diploma in any university or other tertiary institution without the prior approval of the University of Adelaide and where applicable, any partner institution responsible for the joint- award of this degree. I give consent to this copy of my thesis when deposited in the University Library, being made available for loan and photocopying, subject to the provisions of the Copyright Act 1968. I also give permission for the digital version of my thesis to be made available on the web, via the University’s digital research repository, the Library Search and also through web search engines, unless permission has been granted by the University to restrict access for a period of time. I acknowledge the support I have received for my research through the provision of an Australian Government Research Training Program Scholarship. Signature: Date: vii viii Acknowledgements Firstly, I would like to thank my first co-supervisor, Mr. Matthew Trinkle, for being willing to spend his precious time with me together investigating the problems addressed in my research and accompany me during the excursions to perform the air target detection experiments. He is also the person who introduced me to study the topic of GPS bistatic radar. I had learnt a lot of skills in RF electronic system, PCB and FPGA designs from him since I did my undergraduate honours project under his supervision. These knowledges are potentially useful for my future career in the electrical and electronic engineering field. Besides, I would like to thank my second co-supervisor, Prof. Doug Gray, for admitting me as a student member of the Adelaide Radar Research Centre (ARRC), which granted me access to the radar laboratory and numerous resources for designing, testing and building the experimental GPS bistatic radar receiver for my research. Besides, he has provided much useful feedback that greatly improved the writing quality of my thesis. Also, I would like to thank my principal supervisor, Dr. Brian Ng, for his role in supervising and managing my PhD candidature during these years. He provided useful information and advice before I started writing this thesis. He also encouraged me when I at times lost concentration in writing the thesis. There are several staff members at the School of Electrical and Electronic that I am indebted for their assistance and advice. Mr. Danny di Giacomo provided me with a wide range of electronic components suitable for my experimental receiver and placed orders when components were required. Mr. Pavel Simcik helped me to fabricate PCBs for several modules in the system. Ian Linke provided materials for building the receiver’s structure and performed safety inspection for its worthiness in mounting on a car prior to performing the field test. Ms. Rose-Marie Descalzi managed the paperwork and expenses for my travel to conferences. In addition, I would like to thank Dr. Abraham du Plooy from Opt-Osl Systems for fabricating the phased-array elements for the radar receiver. Besides, I would like to thank Dr. ix