Cumulant based algorithms for autofocusing in ISAR/SAR systems

In this paper we present a SAR/ISAR image autofocusing technique based on bispectrum analysis. The noncompensated SAR/ISAR imaging system can be modeled as a bandlimited complex linear time invariant (LTI) filter, so the autofocusing problem is equivalent to the problem of reconstructing the phase of a bandlimited complex LTI system. The complex transfer function of the imaging system is recovered from the estimated bispectrum of the received data by means of an ad-hoc algorithm. The advantage of this technique with respect to those based on the time-frequency analysis is that it allows to compensate for the phase term due to the motion of the radar with respect to the target also in the absence a dominant scatterer in the observed scene