Abstract:This paper presents a signal based Doppler rate estimation and compensation method to form a well focused Ultra-Wide Band Synthetic Aperture Radar (UWB-SAR) image. A refined MapDriftt(MD) autofocus technique is promoted to improve its original performance in UWB-SAR. In the refined MD, some implementation skills are adopted to accommodate the "broadside sparking" and the long aperture. Further more, the estimated Doppler rate error is interpolated and compensated in an iteration manner. As a result, higher order phase errors are compensated and this enable the refined MD technique to be capable in applications with large motion error, for example in UAV SAR. Finally the refined MD technique is verified by real UWB-SAR data imaging.