A Novel NUFFT-Based High-Order Phase Filtering Algorithm for Bistatic SAR

The wavefront curvature error (WCE), which is caused by the planar wavefront assumption in the polar format algorithm (PFA), induces serious degradation to the formed image, especially for the bistatic synthetic aperture radar (BSAR). The existence of a double hyperbola in the bistatic range equation makes it difficult to derive the exact analytical expression for the WCE in the wavenumber domain. Actually, the distortion derives from the first-order WCE and the defocus mainly comes from the quadratic WCE. Moreover, the residual odd-order WCE also affect the main-lobe of the target and the residual even-order WCE lead to the problem of sidelobe asymmetry. To overcome the issues, in this paper, the first-order one-dimensional (1D) Taylor expansion is adopted to effortlessly separate the distortion error and the residual error. The proposed separation strategy can compensate the residual high-order error and maintain the image continuity. In addition, to avoid the interpolation error, which is induced by the wavenumber nonuniformity, the nonuniform fast Fourier transform (NUFFT) is adopted to construct the phase filter. The effectiveness of the proposed algorithm is demonstrated by simulated experiments.