A PROCESSING STRATEGY FOR VARIABLE PRF SAR WITH DIGITAL BEAMFORMING IN AZIMUTH

Conventional synthetic aperture radar (SAR) systems suffer from the contradictory requirements of high resolution and wide swath observation. SAR systems with multiple receive channels in azimuth and/or elevation have been studied and shown to overcome this trade-off. When the system with multiple receive channels in elevation employs variable pulse repetition frequency (PRF) in order to eliminate the blind ranges, it requires azimuth resampling process at some point in the image formation. If the system also has multiple channels in azimuth, then there will be an additional difficulty in the resampling process, because the average PRF is set to be lower than the Doppler bandwidth of the signal received by each receive channel. In this paper, we propose a processing strategy for combining the variable PRF SAR observation with multiple channels both in elevation and azimuth. In the proposed method, multiple azimuth beams are formed at first for each pulse, and azimuth resampling is applied to the signals of each beam. In order to reduce the resampling error, overlapped beams are formed, and only a fraction in the vicinity of the center of the beams are used to reconstruct the full Doppler spectrum.