Image formation for circular scanning synthetic aperture radar (CS-SAR) was investigated. The work principle and echo signal model of CS-SAR were described. A focused image algorithm based on spectrum analysis was presented. This focused algorithm was able to correct the range cell migration within each burst echo of CS-SAR, so it was suitable to form high precision image for CS-SAR. The algorithm flow chart and the deducing process of the algorithm for burst data were given, and the whole process flow chart for CS-SAR based on this algorithm was given also. Compared to classic unfocused Doppler beam sharpening (DBS) algorithm, this algorithm has a little more computational loads but much more imaging precision, compared to extended chirp scaling (ECS) algorithm, it has less precision but much less computational loads. It is competent for fast focused imaging for CS-SAR. The computer simulation results validates that this focused algorithm can be used to image accurately for CS-SAR.
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