Abstract
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.
Highlights
For spaceborne synthetic aperture radar (SAR), the desired radar echoes are received by the antenna after several pulse repetition intervals (PRIs) due to the long distance between the target and the radar
The additional azimuth phase coding introduced by the up and down chirp modulation is derived in this paper, and the range ambiguity suppression effects on both point-liked and distributed targets are analyzed
The attenuation effect of range ambiguous energy would become less effective, but range ambiguous could be still suppressed by the band-passed Doppler filter
Summary
For spaceborne synthetic aperture radar (SAR), the desired radar echoes are received by the antenna after several pulse repetition intervals (PRIs) due to the long distance between the target and the radar. The effect of the additional azimuth phase coding is neglected during derivation of the effect of up and down chirp modulation on point and extended target signals [18]–[21]. The additional azimuth phase coding introduced by the up and down chirp modulation is derived in this paper, and the range ambiguity suppression effects on both point-liked and distributed targets are analyzed. W. Xu et al.: Azimuth Phase Coding by Up and Down Chirp Modulation for Range Ambiguity Suppression
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