Acronyms and Symbols ............................................ v
1 Introduction ................................................. 1
1.1 State-of-the-Art SAR System ............................. 1
1.2 Motivation and Contributions of this Work ............... 3
1.2.1 Challenges in Modem SAR .......................... 4
1.2.2 HRWS SAR Concept ................................. 6
1.2.3 Contributions and Outline of this Work ........... 7
2 Novel MIMO SAR Approach ..................................... 11
2.1 System Configuration ................................... 12
2.1.1 Transmit and Receive Antennas ................... 12
2.1.2 Transceiver Subsystem ........................... 13
2.1.3 Digital Waveform Modulator and Demodulator ...... 13
2.1.4 HRWS SAR Processing Unit ........................ 14
2.2 System Operation ....................................... 14
2.2.1 Data Acquisition ................................ 14
2.2.2 Spatial Sampling Criteria ....................... 16
2.2.3 Multimodal Operation Principles ................. 18
2.3 Generic MIMO SAR Processing ............................ 21
2.4 Challenge in MIMO SAR Implementation ................... 23
2.4.1. Overview of Current Approaches ................. 24
3 Principles of MIMO SAR Techniques ........................... 29
3.1 MIMO SAR Signal Model .................................. 29
3.1.1 MIMO Geometry ................................... 29
3.1.2 MIMO Radar Signal Model ......................... 30
3.1.3 Expansion to the MIMO SAR Signal Model .......... 32
3.2 Digital Beamforming in Elevation ....................... 35
3.2.1 Fundamentals .................................... 35
3.2.2 Multiple Spatial Filtering ...................... 37
3.2.3 SCORE Technique ................................. 40
3.3 Digital Beamforming in Azimuth ......................... 42
3.3.1 Principle of Azimuth Ambiguity Suppression ...... 42
3.3.2 Multichannel Reconstruction Algorithm ........... 43
3.3.3 Minimum Variance Distortionless Response
Method .......................................... 45
3.4 Multiple Subcarrier Technique: OFDM .................... 47
3.4.1 Principle of OFDM ............................... 47
3.4.2 Implementation of OFDM Systems .................. 49
4 Novel Waveform for MIMO SAR ................................. 53
4.1 Orthogonal OFDM Waveforms using Chirp Signals .......... 54
4.1.1 Reinterpretation of Chirp Signal ................ 54
4.1.2 OFDM Modulation using Chirp for Dual Tx
Antennas ........................................ 56
4.1.3 Time Domain Generation .......................... 58
4.1.4 Signal Power Consideration ...................... 60
4.2 OFDM SAR Signal Demodulation ........................... 61
4.2.1 Requirements for the OFDM Demodulation .......... 62
4.2.2 Segmentation: Spatial Filtering ................. 63
4.2.3 Circular-Shift Addition ......................... 65
4.2.4 Demodulation with 2N-DFT ........................ 67
4.2.5 Verification .................................... 69
4.3 Performance Investigation for Doppler Effect ........... 73
4.3.1 Inter-Carrier Interference (IСI) ................ 73
4.3.2 Compression Loss ................................ 76
4.3.3 Doppler Tolerance Improvement ................... 77
4.4 Performance Investigation for Multiple Targets ......... 81
4.4.1 Signal-to-Leakage Power Ratio ................... 81
4.4.2 Speckle Effect .................................. 83
4.5 Coherence Evaluation ................................... 87
4.5.1 Interferometric Coherence ....................... 88
4.5.2 Coherence between Quad-Polarization Data ........ 92
5 System Design Parameters .................................... 97
5.1 Receive Antenna Design Criteria ........................ 97
5.1.1 Receive Antenna Length .......................... 97
5.1.2 Receive Antenna Height .......................... 99
5.1.3 Height of Array Elements in Elevation .......... 101
5.2 Transmit Antenna Design Criteria ...................... 102
5.2.1 Transmit Antenna Height ........................ 102
5.2.2 Transmit Antenna Length ........................ 103
5.3 OFDM Parameters: Δƒ and N ............................. 103
5.4 System Design Example ................................. 104
5.4.1 PRF Selection .................................. 105
5.4.2 Antenna Dimension Specification ................ 105
5.4.3 Summary of Design .............................. 108
5.5 Performance Estimation ................................ 1ll
5.5.1 Noise Equivalent Sigma Zero .................... 1ll
5.5.2 Range Ambiguity-to-Signal Ratio ................ 112
6 Ground-Based Multichannel SAR Demonstrator ................. 115
6.1 System Configuration and Specification ................ 115
6.2 SAR Data Acquisition .................................. 117
6.3 Antenna Subsystem ..................................... 118
6.3.1 Transmit Antenna: Corrugated Pyramidal Horn
Antenna ........................................ 118
6.3.2 Receive Antenna: Microstrip Patch Array ........ 121
6.4 Transceiver Subsystem ................................. 126
6.4.1 Transmitter .................................... 126
6.4.2 Receiver ....................................... 127
6.5. Platform and Operation Software ....................... 132
7 Ground-Based Experiments for MIMO SAR Techniques ........... 135
7.1 Experimental MIMO SAR Processor ....................... 135
7.1.1 Overview ....................................... 135
7.1.2 Channel Balancing .............................. 136
7.1.3 Post-Processing: Higher Order Phase Error
Correction ..................................... 140
7.2 Demonstration of Digital Beamforming in SAR ........... 140
7.2.1 Geometry of the Ground-Based SAR Experiment .... 140
7.2.2 SAR Image Reconstruction with DBF .............. 143
7.3 Digital Beamforming with Non-uniformly Sampled Data ... 152
7.3.1 Geometry and Data Acquisition .................. 152
7.3.2 Ambiguity Suppression Performance .............. 153
7.4 Experiments of MIMO OFDM SAR .......................... 158
7.4.1 Virtual MIMO Antenna Constellation ............. 159
7.4.2 Data Conversion ................................ 160
7.4.3 Processing of MIMO OFDM SAR signal ............. 162
7.4.4 MISO OFDM SAR Experiment ....................... 162
7.4.5 MIMO OFDM SAR Experiment: Multiple Targets
Imaging ........................................ 165
8 Conclusions ................................................ 169
Bibliography .................................................. 181
A DPCA Principle: Geometric Aspect ........................... 185
B Derivation of MVDR Beamformer .............................. 187
C Discrete Signal Theories ................................... 189
C.l. Polyphase Decomposition ............................... 189
C.2. Expansion and Repetition Properties of DFT ............ 190
D Phase Gradient Autofocus Method ............................ 193
E Timing Diagram ............................................. 197
F Low-IF Topology: Image Rejection Principle ................. 199
F.l. Image Rejection Principle ............................. 199
F.2. Effect of I-Q Channel Imbalance ....................... 201
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