Azimuth-Extended Spotlight SAR Based on Multifrequency Subpulse Diversity

Abstract

An azimuth wide-swath spotlight synthetic aperture radar (SAR) imaging method utilizing multifrequency subpulse (MFSP) diversity is proposed. Initially, the MFSP scheme is formulated by dividing the transmit pulse into multiple subpulses, where each is assigned a distinct carrier frequency offset with bandwidth-level spacing. Different subpulses are then steered toward multiple desired subscenes to achieve wide azimuth beam coverage. After receiving the aliased signals from different subscenes, the unambiguous subscene echoes are extracted through a set of bandpass filters. Subsequently, interpolation along the line-of-sight is employed to accurately reconstruct the original sub-images based on the squint geometry of each subscene. Ultimately, following both geometric and radiometric corrections, the complete azimuth-extended spotlight image is generated by merging subscene imagery according to their geometric relationships. Specifically, the key imaging characteristics and parameter design strategies are discussed. The effectiveness of the proposed method is validated through comparisons with traditional methods, demonstrating its capability to expand azimuth width without degrading azimuth resolution or introducing severe wavefront-curvature errors.