Improved Parametric Polar Format Algorithm for High-Squint and Wide-Beam SAR Imaging

High-squint and wide-beam synthetic aperture radar (SAR) imaging is challenging for current popular SAR imaging algorithms, because the severe spatial-variant motion error precludes the precise motion compensation (MOCO). Especially, the azimuth-variant motion error (AVME) would bring not only the azimuth-variant phase error but also the non-negligible nonsystemic range cell migration (NsRCM). This article proposes a novel SAR imaging algorithm to deal with the NsRCM and the azimuth-variant phase error in high-squint and wide-beam SAR imaging. For RCM correction (RCMC), a parametric keystone transform algorithm (PKTA) introducing the three-axis trajectory deviations as parameters is developed. It can correct the nominal RCM and the NsRCM through a time-variant scaling transform along slow time. The robust RCMC paves the way to precisely compensate for the azimuth-variant phase error. In the following, a fast and precise subaperture MOCO algorithm, which applies the recursive discrete Fourier transform (RDFT), is embedded in the azimuth focus procedure to adjust the azimuth-variant phase error. The proposed algorithm can handle the high-squint and wide-beam SAR data with severe motion errors based on these improvements. Finally, extensive experiments with simulated and real-measured SAR data demonstrate the proposal’s superiority and robustness.