Digital Beamforming on Receive: Techniques and Optimization Strategies for High-Resolution Wide-Swath SAR Imaging

Kurzfassung

Synthetic Aperture Radar (SAR) is a well-proven imaging technique for remote sensing of the earth. However, conventional SAR systems are not capable to fulfill the increasing demands for im-proved spatial resolution and wider swath coverage. To overcome these inherent limitations, several innovative techniques have been suggested which employ multiple receive-apertures to gather addi-tional information along the synthetic aperture. This paper reviews these digital beamforming (DBF) on receive techniques with particular emphasis on the multi-aperture signal processing in azimuth and presents a multi-aperture reconstruction algorithm that allows for the unambiguous recovery of the Doppler spectrum. The impact of Doppler aliasing is investigated and an analytic expression for the residual azimuth ambiguities is derived. Further, the influence of the processing on the signal-to-noise-ratio (SNR) is analyzed, resulting in a pulse repetition frequency (PRF) dependent factor describing the SNR scaling of the multi-aperture beamforming network. The focus is then turned to a complete high-resolution wide-swath SAR system design example which demonstrates the intricate connection be-tween multi-aperture azimuth processing and the system architecture. In this regard, alternative process-ing approaches are compared with the multi-aperture reconstruction algorithm. In a next step, optimiza-tion strategies are discussed as pattern tapering, pre-beamshaping-on-receive, and modified processing algorithms. In this context, the analytic expressions for both the residual ambiguities and the SNR scal-ing factor are generalized to cascaded beamforming networks. The suggested techniques can moreover be extended in many ways. Examples discussed in this paper are a combination with ScanSAR burst mode operation and the transfer to multistatic sparse array configurations.