A second order synchrosqueezing S-transform for ISAR imaging

A second order synchrosqueezing S-transform for inverse synthetic aperture radar (ISAR) imaging is proposed in this paper. In the ISAR imaging, the received signal usually tends to appear as a mixture of two typical components, low-frequency stationary rigid body components and high-frequency non-stationary micro-Doppler components. In time-frequency analysis, it should hold a higher frequency resolution in the low frequency region and a higher time resolution in the high frequency region, which is consistent with the characteristics of the S-transform. This paper applies second-order synchrosqueezing to S transform. The time-frequency concentration is significantly improved, while the multi-resolution characteristics of original S-transform is retained. That will provide an effective processing tool for accurate imaging and micro-Doppler characterization. Both simulation and measured data show that the proposed method can well represent the micro-Doppler information of the target while improving the accuracy of rigid body imaging.