Abstract
Scan-on-receive (SCORE) digital beamforming (DBF) in elevation can significantly improve the signal-to-noise ratio (SNR) and suppress range ambiguities in spaceborne synthetic aperture radar (SAR). It has been identified as one of the important methods to obtain high-resolution wide-swath (HRWS) SAR images. However, with the improvement of geometric resolution and swath width, the residual pulse extension loss (PEL) due to the long pulse duration in the conventional spaceborne onboard DBF processor must be considered and reduced. In this paper, according to the imaging geometry of the spaceborne DBF SAR system, the reason for the large attenuation of the receiving gain at the edge of the wide swath is analyzed, and two improved onboard DBF methods to mitigate the receive gain loss are given and analyzed. Taking account of both the advantages and drawbacks of the two improved DBF methods presented, a novel onboard DBF processor with multi-frequency and multi-group time delays in HRWS SAR is proposed. Compared with the DBF processor only with multi-group time delays, the downlink data rate was clearly reduced, while focusing performance degradation due to phase and amplitude errors between different frequency bands could be mitigated compared with the DBF processor only with multi-frequency time delays. The simulation results of both point and distributed targets validate the proposed DBF processor.
Highlights
Synthetic aperture radar (SAR) is a powerful active microwave remote sensing system that can be used in almost all weather and time conditions
Seven point targets could be well compressed by the matched filter after the proposed digital beamforming (DBF) processor, as shown in Figure 11c, while interpolations of compression results of the nearest, middle, and farthest targets are shown in Figure 11d, which show the good pulse compression behavior
DBF with multiple sub-apertures uniformly distributed in elevation can be widely adopted in future spaceborne SAR missions to achieve the High-resolution wide-swath (HRWS) imaging capacity
Summary
Synthetic aperture radar (SAR) is a powerful active microwave remote sensing system that can be used in almost all weather and time conditions. For conventional spaceborne SAR systems, wide swaths require a lower pulse repetition frequency (PRF), which will limit the azimuth resolution. Hampered by this contradiction, conventional spaceborne SAR cannot acquire imaging capacities of high resolution and wide swaths simultaneously [6,7]. Conventional spaceborne SAR cannot acquire imaging capacities of high resolution and wide swaths simultaneously [6,7] To overcome this problem, multiple new technologies and modes have been proposed in recent years, such as signal reconstruction [8,9], space-time adaptive processing (STAP) [10], and digital beamforming (DBF) [11,12,13,14].
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