In multiple-input multiple-output synthetic aperture radar (MIMO⁻SAR) signal processing, a reliable separation of multiple transmitted waveforms is one of the most important and challenging issues, for the unseparated signal will degrade the performance of most MIMO⁻SAR applications. As a solution to this problem, a novel APC⁻MIMO⁻SAR system is proposed based on the azimuth phase coding (APC) technique to transmit multiple waveforms simultaneously. Although the echo aliasing occurs in the time domain and Doppler domain, the echoes can be separated well without performance degradation by implementing the azimuth digital beamforming (DBF) technique, comparing to the performance of the orthogonal waveforms. The proposed MIMO⁻SAR solution based on the APC waveforms indicates the feasibility and the spatial diversity of the MIMO⁻SAR system. It forms a longer baseline in elevation, which gives the potential to expand the application of MIMO⁻SAR in elevation, such as improving the performance of multibaseline InSAR and three-dimensional SAR imaging. Simulated results on both a point target and distributed targets validate the effectiveness of the echo separation and reconstruction method with the azimuth DBF. The feasibility and advantage of the proposed MIMO⁻SAR solution based on the APC waveforms are demonstrated by comparing with the imaging result of the up- and down-chirp waveforms.
Keywords: azimuth phase coding (APC); digital beamforming (DBF); multiple-input multiple-output synthetic aperture radar (MIMO–SAR); orthogonal waveforms; radar system.