A subspace algorithm of calibrating channel gain and phase errors for HRWS SAR imaging

Azimuth multichannel SAR system is a promising solution to achieve high-resolution and wide-swath (HRWS) imaging for spaceborne synthetic aperture radar (SAR) system. These spectrum components within a Doppler bin can be considered as virtual signal sources from different known directions. Thus the azimuth signal of multichannel SAR can be reconstructed via digital beamforming (DBF) techniques. However, the performance of restoring Doppler full spectrum degrades significantly due to the existence of channel gain and phase errors in azimuth multichannel SAR system. In this paper, a subspace calibration algorithm is proposed for the HRWS SAR imaging system. The fundamental idea behind the proposed algorithm is that the signal subspace is equivalent to the space spanned by the practical steering vectors of the multichannel SAR system. Moreover, we discuss the uniqueness of the calibration of the proposed method. Finally, real airborne multichannel SAR data processing demonstrates that the proposed method can effectively and excellently calibrate the channel gain and phase errors.