This paper analyzes the azimuth spectrum folding problem which arises from the dependence of the Doppler centroid on range frequency in squinted spotlight synthetic aperture radar (SAR). Based on the analysis, a novel approach for squinted spotlight SAR is proposed in this paper. In this approach, an azimuth preprocessing step including a deramping operation and an operation of azimuth spectrum replicating and filtering is introduced to eliminate spectrum folding problem. Then, a modified Range Migration Algorithm (RMA) is adopted to process the preprocessed data. This approach extends the focusing capacity of traditional two-step processing approach from broadside spotlight SAR to squinted case. Moreover, this approach is e±cient due to a limited azimuth data extension to resolve the spectrum aliasing problem. Experimental results on simulated raw data validate the proposed approach.
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