Two-stage channel calibration technique for multichannel synthetic aperture radar-ground moving target indication systems

Multichannel synthetic aperture radar (SAR) provides a powerful means for ground moving target indication (GMTI) purpose. The channels are often mismatched because of various kinds of errors. However, perfectly calibrated channels are always needed to perform an effective GMTI. In this study, the authors present a two-stage channel calibration technique to compensate the channel errors. The authors find that the channel errors can be classified into two categories, that is, the so called convolutional and multiplicative errors. The convolutional errors are more suitable to be compensated in two-dimensional (2-D) frequency domain, whereas the multiplicative errors should be compensated in image domain. The authors show that the convolutional errors can be effectively compensated by a Stage 1 calibration filter, in which the conventional 2-D frequency domain calibration methods can be employed. To compensate the multiplicative errors, the authors introduce a median filter as a Stage 2 calibration filter in the image domain. The proposed two-stage technique is tested with real SAR data obtained from terribly mismatched channels and is found to work well.