A Highly-Squinted TOPSAR Image Formation and Azimuth Resolution Enhancement Using Embedded Focusing Based on Hybrid-Domain Algorithm

TOPSAR has operational advantages over conventional synthetic aperture radars (SARs) by steering the beam in the azimuth direction. However, because of its complex observation geometry, azimuthal degradation occurs when the illumination mode is highly-squinted. In the context of highly-squinted TOPSAR (HS-TOPSAR), targets symmetrically positioned along the flight path exhibit nearly identical Doppler histories, leading to ambiguities, whereas beam steering narrows and skews the spectrum, diminishing signal orthogonality and introducing spectral folding. Consequently, the Doppler gradient diminishes to a degree that makes precise measurement challenging, thereby constraining fine azimuth angular resolution during imaging. To this end, a hybrid-domain algorithm utilizing azimuth iterative focusing is proposed to address azimuth-variant characteristics, resolving ambiguities and enhancing spectral orthogonality for image reconstruction, as verified by simulation results and metrics.