Abstract
The paper proposes special multiple-input single-output synthetic aperture radar (MISO-SAR) and multiple-input multiple-output SAR (MIMO-SAR) for bidirectional imaging, which can simultaneously illuminate two areas from different directions in azimuth. For the proposed MISO-SAR, two subpulses with the same carrier frequency and phase coding are transmitted with different azimuth directions by switching the phase coefficients in the transmit modules, and echoes corresponding to the subpulses are received by the main lobe and the first grating lobe of the whole antenna. To suppress mutual interference, the two subpulses are transmitted with different range-frequency bands, and their echoes are demodulated and recorded in different channels in the proposed MIMO-SAR. This paper presents the system design of these modes and analyzes their azimuth ambiguity to signal ratio (AASR). Besides, simulation results on points are carried out to validate the proposed bidirectional imaging modes.
Highlights
The repeated acquisition of synthetic aperture radar (SAR) images is very useful for multiple observation applications, such as moving targets detection, terrain change detection, and velocity measurements by along-track interferometry [1,2,3]
For the desired azimuth ambiguity to signal ratio (AASR) level as shown in Figure 4, the selected pulse repetition frequency (PRF) should be more than 6500 Hz in the single channel bidirectional SAR system, while the selected PRF only should be more than 5100 Hz in the proposed MISO-SAR system
The paper has put forward two novel imaging modes named MISO-SAR and MIMO-SAR for bidirectional imaging, and both modes allow for single-satellite short-term repeated SAR acquisitions in the range of seconds
Summary
The repeated acquisition of synthetic aperture radar (SAR) images is very useful for multiple observation applications, such as moving targets detection, terrain change detection, and velocity measurements by along-track interferometry [1,2,3]. The single channel bidirectional SAR imaging mode is proposed in [1] and implemented via a phased planner antenna to generate both main lobe and grating lobes to illuminate different areas. This imaging mode was first achieved by TerraSAR-X satellite [6,7,8,9,10]. Two subpulses are transmitted in turn with different azimuth antenna beams by switching the phase coefficients in the transmit modules, and echoes of the two subpulses are simultaneously received by the main lobe and the first grating lobe of the whole antenna and recorded in a single channel This imaging scheme with two transmitted subpulses and a single receive channel is named as multipleinput single-output SAR (MISO-SAR) for bidirectional imaging.
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