Time-varying step-transform algorithm for high squint SAR imaging

High-squint angle synthetic aperture radar (SAR) imaging has applications i n specific situations such as providing looking angle-dependent scattering information and revisiting an area of interest. It is very difficult for cu rrent SAR-imaging algorithms to be used directly in high-squint configurati ons. This is due to the large range-cell migration and the nonnegligible cu bic-phase term in the signal. In this paper, an improved algorithm called t he time-varying step-transform algorithm is proposed. It uses different chi rp rates to deramp the signal in different subapertures to alleviate the ra nge-focus problem. The interval between subapertures is also varied accordi ng to the deramping chirp rate. The nonnegligible cubic-phase term is inclu ded in the focusing procedure. The performance of the proposed algorithm in high-squint-angle mode is excellent, By reducing the subaperture length as the squint angle is increased, the performance of the algorithm is almost independent of squint angle. The proposed algorithm is also flexible for mu ltilook processing and motion-error compensation.