A Unified Postprocessing Framework for Beam-Steering Mode Back-Projection SAR Imaging

The back-projection (BP) algorithm has the capability for unified processing of nonlinear trajectories and different imaging modes, with low pulse repetition frequency requirements, meeting the growing demands of SAR imaging for higher resolution and wider swaths, and thus has broad application prospects. Although unified imaging is achievable in practical applications, the main challenges in processing beam-steering mode BP images lie in defocusing and high sidelobe issues, which are difficult to resolve. Therefore, researching postprocessing techniques is an important foundation for expanding the application scope of BP. For this aim, a unified postprocessing framework for beam-steering mode BP SAR imaging is proposed in this article. In this framework, a BP grid layout strategy with minimal errors is introduced to reduce error magnitude and estimation difficulty. Then, the beam-steering mode BP spectrum is uniformly analyzed, and a unified spectrum compression function is constructed into the BP process, enabling the autofocus algorithm to be used for motion error elimination. Finally, an azimuth time-domain windowing method for tracking the beam is proposed to suppress sidelobe amplitude and clutter signals introduced by sidelobes. Through the postprocessing method proposed in this article, imaging and postprocessing operations can be completed on any plane, requiring only one imaging process.