 | Hubert S. Spaceborne SAR systems with digital beamforming and reflector antenna / Deutsches Zentrum für Luft-und Raumfahrt, Institut für Hochfrequenztechnik und Radarsysteme, Oberpfaffenhofen. - Köln: DLR, 2014. - xv, 217 p.: ill. - (Forschungsbericht; 2014-09). - Bibliogr.: p.204-217. - 150 р. - Пер. загл.: Космические радиолокационные системы с синтетической апертурой с цифровым формированием луча и рефлекторной антенной. - ISSN 1434-8454
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Acronyms and Symbols ............................................ v
1 Introduction ................................................. 1
1.1 A Brief Historical Review ............................... 2
1.2 State-of-the-art and Motivation ......................... 3
1.3 Scope of the Work ....................................... 6
2 Theoretical Background ....................................... 9
2.1 Radar Scattering ........................................ 9
2.1.1 The SAR Imaging Equation ........................ 12
2.2 Spectral Representation of Point Targets ............... 14
2.2.1 Ewald Sphere Constructions ...................... 18
2.2.2 SAR Systems and Resolution ...................... 20
2.2.3 SAR Signal Sampling ............................. 22
2.3 SAR Signals and Ambiguities ............................ 24
2.4 Signal-to-Noise Ratio .................................. 27
3 Conventional SAR Systems .................................... 28
3.1 Comparison: Planar versus Reflector Antenna SAR
System ................................................. 29
3.1.1 Planar Array Antennas ........................... 30
3.1.2 Array-fed Reflector Antennas .................... 32
3.2 Wide-Swath SAR System Operation ........................ 40
3.3 Limitations ............................................ 44
4 Multi-Channel Reflector SAR Systems ......................... 49
4.1 Multi-Channel Reflector SAR System Model ............... 51
4.1.1 The Narrowband Approximation .................... 53
4.2 Digital Beamforming for Side-Looking SAR Systems ....... 55
4.2.1 Digital Beamforming and Extended Pulses ......... 56
4.2.2 Digital Beamforming with Range Compressed Data .. 58
4.2.1 Digital Beamforming in the Time-Wavenumber
Domain .......................................... 60
4.2.4 Digital Beamforming in 3-D Time-Wavenumber
Space ........................................... 62
4.3 Optimal Beamforming Techniques ......................... 64
4.3.1 Cost Function and Constraints ................... 65
4.3.2 Beamforming by Channel Switching ................ 69
4.3.3 Minimum Variance Distortionless Response
Beam-forming .................................... 71
4.3.4 Linear Constraint Minimum Variance Beamforming .. 73
4.4 Beamforming with Spaceborne Reflector SAR Sensors ...... 76
4.4.1 Digital Beamforming in Elevation ................ 80
4.4.2 Digital Beamforming in Azimuth .................. 90
4.4.3 Digital Beamforming for Polarimetrie
Applications .................................... 97
5 Reflector SAR System Design Example ........................ 104
5.1 Reflector Design Equations ............................ 104
5.1.1 Reflector and Feed Array Design in Azimuth ..... 109
5.1.2 Reflector and Feed Array Design in Elevation ... 111
5.2 System Performance .................................... 113
5.2.1 Elevation Performance .......................... 115
5.2.2 Azimuth Performance ............................ 127
5.2.3 Polarimetrie Performance ....................... 140
5.3 Error and Sensitivity Analysis ........................ 143
6 Optimization Strategies .................................... 150
6.1 Digital Beamforming with Robust Constraints ........... 150
6.1.1 The Digital Sidelobe Canceller ................. 151
6.1.2 LCMV Beamforming as Spatial Band-Stop Filter ... 153
6.2 A Reflector Concept Robust against Feed Failures ...... 157
6.2.1 One-dimensionally Defocused Reflector
Antennas ....................................... 158
6.2.2 Performance .................................... 161
6.2.3 Performance under Failure Conditions ........... 164
6.2.4 Discussion ..................................... 165
7 Digital Beamforming Demonstrator ........................... 168
7.1 Data Preprocessing .................................... 170
7.2 Demonstration of Principle: Unity and MVDR
Beamforming ........................................... 171
7.3 A DBF Experiment in Elevation ......................... 174
7.3.1 Discussion ..................................... 177
8 Conclusions ................................................ 179
8.1 Outlook ............................................... 181
A Electromagnetic Scattering ................................. 183
A.1 Field Solutions ....................................... 184
В Linearly Filtered Processes ................................ 189
С Matched Filtered Chirp Signals ............................. 193
D Quadratic Optimization ..................................... 195
E SNR for Time-Variant Beamformers ........................... 197
F Optimal Time-Variant Beamforming ........................... 200
G Integrated and Peak-Sidelobe Ratio ......................... 202
H Hilbert Transform Relations ................................ 203
Bibliography .................................................. 204
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