Far-Field Limit of PFA for SAR Moving Target Imaging

A new formulation of the polar format algorithm (PFA) for spotlight synthetic aperture radar (SAR) imaging is presented, which is useful when investigating its response to the moving target. Our work starts with examining the commonly adopted implementation of the PFA, i.e., the separable 1-D range and azimuth resampling procedures for their roles in range cell migration (RCM) correction, respectively. It is shown that the former performs RCM predeformation, while the latter is, substantially, the combination of RCM linearization and the keystone transform (KT), i.e., a well-known technique for SAR imaging of moving targets. The new formulation approach is applied to analyze the moving target. The far-field limit of the PFA for moving target focusing is derived, which can be used to predict the target´s impulse response (IPR) function. The work presented might be helpful when considering a SAR system with the capability of ground moving target indication and imaging (GMTI&Im).