I. Introduction
Synthetic aperture radar (SAR) is a well-proven remote sensing technique, which obtains its high range resolution by utilizing the transmitted wide-band waveform and high azimuth resolution by exploiting the relative motion between the target and the radar platform [1]. However, current single-antenna SAR systems cannot provide simultaneously high-resolution and wide-swath (the width of the ground area covered by the radar beam) imaging [2]. To improve azimuth resolution, a smaller along-track antenna length and a higher pulse repetition frequency (PRF) are required. But, correspondingly the unambiguously imaged swath width will be decreased with the increase of the PRF. There is therefore a clear incentive consideration to increase swath width and azimuth resolution simultaneously. Several multi-aperture on receive-based solutions have been investigated previously by other authors [3]–[6]. The basic idea is to use multiple receive channels to gather additional information and to benefit from this information to overcome the restrictions in conventional SAR systems.