A Quadtree Beam-segmenting based Wide-Swath SAR Polar Format Algorithm

The Polar Format Algorithm (PFA) is the most suitable imaging algorithm for high-resolution and highly-squinted spotlight Synthetic Aperture Radar (SAR), but the approximation of planar wavefront in this algorithm limits the effective scene size of PFA. To meet the wide-swath requirement in modern SAR system, a quadtree beam-segmenting based PFA is proposed in this paper. The original full-beam echo signal is filtered recursively as a quadtree, generating multiple sub-beams. Each sub-beam only illuminates a small part of the total swath. As long as the sub-beam is narrow enough, standard PFA could be utilized to process the sub-beam data. Each sub-beam data will result in a fully focused sub-image. Finally, all fully focused sub-images are mosaicked to get a big image perfectly focused. This divide-and-conquer approach breaks the image size limit in traditional PFA, extensively enlarges the effective scene. The processing flows are derived in detail and the algorithm is validated by simulated and measured data. Via the experiments, it could be seen that when the scene size exceeds the PFA limit, there would be serious defocus in the image obtained by traditional PFA, and the defocus could be eliminated by our new approach.