A Modified Multistep Frequency-Scaling Algorithm for Ground-Based FMCW-ArcSAR Imaging

Arc synthetic aperture radar (ArcSAR) enables panoramic, high-angular-resolution imaging through platform rotation, overcoming the field-of-view limitations of linear-rail SAR. However, conventional ArcSAR algorithms based on low-order series expansions and reference-range approximations suffer from phase errors at millimeter-wave frequencies, resulting in azimuth defocusing. Moreover, as the azimuth bandwidth increases for close-range targets, bandwidth broadening can cause overcorrection when far-range assumptions break down. This paper introduces the Frequency Scaling Algorithm (FSA) into ArcSAR and proposes an enhanced Multi-Step Frequency Scaling Algorithm (MSFSA). Unlike conventional FSA, which performs scaling solely in the range domain, MSFSA incorporates a Doppler-domain frequency-scaling step prior to range cell migration correction (RCMC). Differential and bulk RCMC are then performed based on Taylor-series expansion and series inversion, followed by a second azimuth-frequency-scaling step to restore phase fidelity. With the integration of precise azimuth matched filtering, overall image quality is further improved. Simulation and experimental results using frequency-modulated continuous-wave (FMCW) radar demonstrate that MSFSA achieves imaging performance comparable to the Range Doppler Algorithm (RDA) with sinc interpolation and the Back Projection Algorithm (BPA), while maintaining higher computational efficiency by avoiding interpolation and point-by-point processing. Compared with existing methods, MSFSA provides superior close-range imaging quality and reduced far-range phase error, making it a promising technique for high-resolution, wide-swath ArcSAR imaging.