I. Introduction
Azimuth multichannel synthetic aperture radar (SAR) is widely utilized in ground observation in both military and civilian fields [1]–[4]. However, using a multiaperture antenna with fixed phase centers, azimuth uniform sampling can be obtained only when the pulse repetition frequency (PRF) takes the fixed optimum value, which is rarely took by actual systems. If uniformly distributed samples cannot be ensured, azimuth paired ambiguities in the image will be caused and imaging quality will be severely decreased [5]–[9].