In multi-circular synthetic aperture radar (MCSAR) mode, resolution and sidelobes are two important parameters to consider when representing imaging quality, as in other SAR imaging modes. In this paper, three-dimensional (3-D) resolution and cone-shaped sidelobes of MCSAR are analyzed for a point target in the scene center under the Nyquist sampling criterion. The results of the analysis show that resolution can be improved, and cone-shaped sidelobes can be suppressed by increasing the system bandwidth and the length of synthetic aperture in the elevation direction. But this will make the system of acquiring data more difficult. It turns out that some digital signal processing techniques can enhance 3-D imaging quality of MCSAR. In this paper, a simple method based on spectrum extrapolation and interferometric phase masking is proposed to improve 3-D resolution and suppress cone-shaped sidelobes of MCSAR. Experimental results regarding a tank model in a microwave anechoic chamber demonstrate that this method is effective.
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