Azimuth Phase Coding by Up and Down Chirp Modulation for Range Ambiguity Suppression

High range ambiguity level will impair the spaceborne SAR image quality and hamper following SAR image applications. The range ambiguity suppression effect of the up and down chirp modulation on spaceborne SAR images is analyzed in this paper. Without taking care of ambiguity signal suppression in azimuth, the mere use of up and down chirp modulation signal would be only useful for point-liked targets and void for distributed targets. The additional azimuth phase coding introduced by the up and down chirp modulation is analyzed in this paper, and it results in Doppler spectra of part of range ambiguities shifting. Therefore, range ambiguity energy would be suppressed for both point-liked and distributed targets in spaceborne SAR with the up and down chirp modulation. The range ambiguity suppression effects of the up and down chirp modulation on both point-liked and distributed target are analyzed, and simulation results validate the presented analysis results.