Residual high-order wavefront curvature error compensation for the polar format algorithm in widefield spotlight SAR imaging

Abstract

ABSTRACT Polar format algorithm (PFA) is an efficient image formation algorithm for spotlight-mode synthetic aperture radar (SAR). However, the derivation of PFA relies upon the approximation of planar wavefront, and the resulting wavefront curvature error (WCE) causes severe SAR image degradation, e.g., distortion and defocus. The distortion stems from the first-order WCE and the defocus mainly comes from the quadratic WCE. To eliminate the defocusing effects, the existing space-variant post-filtering algorithms (SVPFAs) mainly compensate the quadratic term of WCE and ignore the residual high-order terms. Actually, the residual odd-order WCE will also broaden the main-lobe of the target and the residual even-order WCE will lead to the problem of sidelobe asymmetry. To tackle these issues, this letter proposes a modified SVPFA to correct both the quadratic and the residual high-order WCE. First, based on the derivation of PFA, the accurate expression of WCE is obtained. Second, the quadratic and residual high-order WCE are separated without complicated high-order two-dimensional Taylor expansion. Finally, the WCE is corrected by phase compensation and geometric distortion correction, respectively. The effectiveness of the proposed algorithm is verified by simulation experiments.