Efficient BiSAR PFA Wavefront Curvature Compensation for Arbitrary Radar Flight Trajectories

The polar format algorithm (PFA) is a popular choice for general bistatic synthetic aperture radar (BiSAR) imaging due to its computational efficiency and adaptability to situations with complicated geometries or arbitrary flight trajectories. However, efficient and accurate compensation of 2-D residual phase errors induced by the wavefront curvature remains challenging when obtaining high-quality BiSAR PFA images. In this article, an analytical expression for the phase errors in the wavenumber domain is derived. With this, the inherent structural characteristics of the phase errors are formulated, where the 2-D phase errors can be reduced to 1-D phase errors for an optimal coordinate system. Moreover, the mapping relationship between distorted point targets in the optimal imaging coordinates and their actual point targets in the original imaging coordinates is investigated. By exploiting the structural characteristics and the mapping relationship, a highly efficient BiSAR PFA wavefront curvature compensation method is proposed. This allows a reduced-dimensional space-variant filter to be constructed to mitigate the 2-D defocusing effect without compromising the compensation accuracy, with the distortion correction being performed using interpolation. The proposed method significantly reduces the complexity required for residual 2-D phase error compensation while simplifying the distortion correction, resulting in notable robustness. The effectiveness of the method is demonstrated using point target and scene target simulations.