A multiple-subapertures autofocusing algorithm for circular SAR imaging

Due to trajectory complexity of circular synthetic aperture radar (CSAR), it is very difficult to compensate motion errors accurately using conventional frequency-based SAR autofocusing approaches. With point-by-point coherent integration, autofocus back projection (ABP) algorithm is promising for motion error correction in the case of complex trajectory. However, the exiting ABP methods usually assume that the radar cross section (RCS) of targets are constant in a synthetic aperture time, which are not suitable for wide-angle CSAR imaging. In addition, these ABP algorithms also suffer from less accuracy and time-consuming. To overcome the above disadvantages of ABP and compensate motion error of CSAR, a novel method is proposed in this paper. In the scheme, the full aperture data of CSAR is firstly divided into serval sub-apertures, and then the phase errors in each sub-aperture are estimated based ABP algorithm. Furthermore, to improve computational efficacy, only dominant scatters are selected to estimate these phase errors in each sub-aperture. Different simulation results demonstrate the effectiveness of the method.