Zusammenfassung ................................................. v
Abstract ...................................................... vii
Acronyms and Symbols ........................................... ix
1 Introduction .................................................. 1
1.1 State-of-the-Art: Synthetic Aperture Radar Remote
Sensing ................................................... 2
1.2 Motivation, Scope, and Structure of this Work ............. 5
2 Conventional SAR Systems-Fundamentals and Constraints ......... 9
2.1 Geometry and Principle .................................... 9
2.2 SAR Signal Model ......................................... 12
2.3 Pulsed Signal Acquisition ................................ 17
2.3.1 Azimuth Ambiguities ................................ 17
2.3.2 Range Ambiguities .................................. 19
2.4 Constraints .............................................. 20
3 Multi-Channel SAR - An Overview .............................. 23
3.1 Multiple Aperture Reception .............................. 23
3.2 Overview of Historical Developments ...................... 24
3.3 First System Concepts .................................... 26
3.3.1 Multiple Apertures in Elevation .................... 26
3.3.2 Displaced Phase Center Antenna in Azimuth .......... 26
3.3.3 Quad Array Antenna ................................. 27
3.4 Processing Strategies .................................... 27
3.4.1 Scan-on-Receive in Elevation (SCORE) ............... 28
3.4.2 Multi-Channel Reconstruction Algorithm in
Azimuth ............................................ 28
3.4.3 Multi-Channel Phase Correction in Azimuth .......... 29
3.4.4 Minimum Variance Distortionless Beamformer ......... 29
3.5 Alternative Approaches ................................... 29
3.5.1 Multiple Beam SAR .................................. 30
3.5.2 Spread Spectrum Waveforms .......................... 31
3.5.3 Sparse Array SAR Constellations .................... 31
4 Multi-Channel SAR in Azimuth ................................. 33
4.1 Multi-Channel Reception in Azimuth ....................... 33
4.2 Multi-Channel Impulse Response and Quadratic
Approximation ............................................ 35
4.3 Spatial Sampling ......................................... 38
4.3.1 Effective Phase Center, Virtual Sample Position
and Spatial Sampling ............................... 38
4.3.2 Uniform Sampling ................................... 40
4.3.3 Special Sampling Scenarios ......................... 41
5 Multi-Channel Azimuth Processing: Reconstruction Algorithm ... 43
5.1 Theoretical Background ................................... 44
5.2 Illustration of Principle ................................ 47
5.3 Multi-Channel Reconstruction in the Framework of STAP .... 49
5.4 Two-Dimensional Reconstruction and Processing ............ 50
5.4.1 Multi-Channel Range Cell Migration ................. 50
5.4.2 Reconstruction Filter Mismatch ..................... 52
5.4.3 Two-Dimcnsional Multi-Channel Reconstruction ....... 53
5.5 Signal Power ............................................. 54
5.6 Residual Reconstruction Error and Azimuth Ambiguities:
AASRN .................................................... 56
5.7 SNR Scaling in Digital Beamforming Networks: Φbf ......... 60
5.8 Noise Equivalent Sigma Zero (NESZ) in Multi-Channel
SAR ...................................................... 66
6 Demonstration With Airborne Measured Data .................... 69
6.1 Reconstruction of E-SAR Measured Data .................... 69
6.2 Reconstruction of F-SAR Measured Data .................... 73
6.2.1 System Setup ....................................... 74
6.2.2 Processing Results ................................. 76
7 System Design Example ........................................ 83
7.1 Requirements and Timing .................................. 83
7.2 System Parameters ........................................ 85
7.2.1 Azimuth Parameters ................................. 85
7.2.2 Cross-Track Parameters ............................. 88
7.3 Simulation Environment ................................... 89
7.4 System Performance ....................................... 89
7.4.1 Azimuth-Ambiguity-to-Signal Ratio: AASRN ........... 90
7.4.2 Geometric Resolution in Azimuth: δaz ............... 92
7.4.3 Signal Peak Power: ps,max ........................... 93
7.4.4 SNR Scaling - Prediction and Simulation ............ 93
7.4.5 Azimuth Loss: Lal ................................... 96
7.4.6 Noise Equivalent Sigma Zero: NESZ .................. 97
8 Optimization Potentials ...................................... 99
8.1 Error Sources and Optimization Approaches ................ 99
8.2 Optimized Parameter Setup: Adaptation of Processed
Doppler Bandwidth ....................................... 101
8.3 Adaptive PRF Management in Sparse Array Systems ......... 102
8.4 Pattern Tapering on Transmit ............................ 103
8.5 Optimized System Design Example ......................... 107
8.6 Phase Center Adaptation on Transmit ..................... 109
8.6.1 System Architecture and Basic Principle ........... 109
8.6.2 Analytic Description .............................. 111
8.6.3 Performance Analysis .............................. 113
8.7 Cascaded Beamforming Networks ........................... 115
8.7.1 System Architecture and Extended System Model ..... 116
8.7.2 Phase Center Adaptation ........................... 119
8.7.3 Compensation for Power Loss in Analog Networks .... 122
8.7.4 Signal Power ...................................... 122
8.7.5 Residual Reconstruction Error and Azimuth
Ambiguities: AASRN,BD............................... 124
8.7.6 SNR Scaling in Cascaded Beamforming Networks:
Φbf,c .............................................. 125
8.7.7 Performance Analysis I - Analog Pre-Beamshaping
on Receive ........................................ 127
8.7.8 Performance Analysis II - Adapted Digital
Beamforming ....................................... 130
9 Multi-Channel Reconstruction in Burst Mode Operation ........ 139
9.1 Motivation of Multi-Channel Burst Mode Systems .......... 139
9.2 Burst Mode Operation .................................... 141
9.2.1 ScanSAR Timing .................................... 141
9.2.2 Burst Mode Target Signal Spectrum ................. 141
9.3 Burst Mode Signal Power ................................. 143
9.4 Azimuth Ambiguities in Burst Mode Operation: AASRN,B ..... 144
9.5 SNR Scaling in Burst Mode Operation: Φbl,B ............... 145
9.6 System Design Example - Multi-Channel ScanSAR ........... 145
9.6.1 Timing and System Parameters ...................... 146
9.6.2 Performance Analysis .............................. 148
9.7 Multi-Channel TOPS Mode ................................. 150
9.7.1 Performance Analysis .............................. 151
9.7.2 Adaptively Squinted Multi-Channel Processing
for TOPS .......................................... 153
10 Discussion ................................................. 157
10.1 Conclusion- Achieved Objectives of the Work ........... 157
10.2 Summary of Results .................................... 158
10.3 Outlook ............................................... 160
Bibliography .................................................. 163
A History of Spaceborne SAR Missions .......................... 171
B Spherical SAR Geometry ...................................... 173
C Quadratic Approximation of Range History .................... 177
D Analogy of Null-Steering and Multi-Channel Reconstruction ... 183
E SNR in Multi- and Mono-Aperture Systems ..................... 187
F SNR Scaling - Further Interpretations ....................... 191
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