Spotlight SAR mode can achieve high resolution radar imaging, but the measurement error, radar platform motion
and the other reasons, will make the image suffer the severe defocus and even distortion. This paper introduces the
range alignment technology of ISAR imaging to Spotlight SAR imaging,and improved the MD-PGA algorithm, so as to
make motion compensation for the error.Afterwards, with the improved Space-variant post filtering method, compensate
the wavefront curvature error to improve the image quality. Finally the processing results of measured data showed the effectiveness
of this method.