Wide swath, high resolution SAR using multiple receive apertures

When one attempts to image a large area while maintaining high resolution, ambiguities often appear. This occurs when the number of pixels exceeds the number of measurements or when the area includes range-Doppler ambiguities. In fact, the number of independent samples obtained by a single-receiver SAR, and consequently the number of pixels that can be unambiguously imaged, is equal to the time-bandwidth product of the radar signal. It is shown that multiple receive apertures resolve this scenario by adding independent angle-of-arrival samples to the system. Because targets that are ambiguous in range and Doppler are not ambiguous in angle of arrival, an image with the same resolution as the single-aperture image, but with larger area, is unambiguously obtained. The authors present a multiple-aperture configuration, each with coherent receivers. The SAR image is calculated using three methods. The first is the traditional matched-filter method. The second is an orthogonal filter method. Last, a sidelobe cancellation filter is applied. The methods are applied after each aperture is range-Doppler processed. Therefore, the methods are used to resolve the ambiguities inherent in traditional range-Doppler processing.