A novel PGA technique for circular SAR based on echo regeneration

Circular SAR (CSAR) can obtain images of high resolution. However, the image quality is very sensible to sub-wavelength motion errors caused by platform position uncertainty. Due to the limit of accuracy of the inertial measurement units (IMU) systems, a robust autofocus technique has to be used to cope with the demands of CSAR image formation. Because of the serious coupling between range and azimuth, and also the spatial-variant property of the phase error in the spatial frequency domain, the robust Phase Gradient Autofocus (PGA) technique that widely used in conventional spotlight SAR with a straight path can not readily be applied to CSAR. In this paper, a novel PGA technique for CSAR based on echo regeneration is presented to reduce the accuracy requirement from the order of a wavelength to the order of a range cell. The proposed approach is validated via simulation.