Frequency-Domain Autofocus Method for High-Squint SAR BP Images

In high-squint synthetic aperture radar (SAR) imaging, the two-dimensional (2-D) coupling and spatially variant characteristics of motion errors severely degrade signal coherence, leading to significant 2-D defocusing artifacts. This paper proposes a frequency-domain autofocus method for high-squint SAR Back-Projection (BP) images. An affine coordinate (AC) system is constructed to partition imaging grids, enabling rapid BP imaging while significantly reducing non-systematic range cell migration (NSRCM) and range defocusing terms in BP images, thereby improving phase error estimation accuracy. A spectrum alignment processing method is introduced to eliminate aliasing effects, ensuring precise estimation of azimuth phase error (APE). Leveraging the prior phase error structure derived from BP image spectra, the estimated APE is inverted into 2-D phase errors to achieve high-precision compensation. Simulation experiments validate the effectiveness of the proposed algorithm in high-squint SAR scenarios.