High-resolution radar images can be achieved by employing synthetic aperture radar (SAR) or inverse synthetic aperture radar (ISAR) techniques. It can be shown that SAR and ISAR have the same underlying theory but different configuration. Here the specific problem of aircraft ISAR imaging using ground-based radar is Addressed. Three ISAR imaging scenarios, namely ISAR imaging with the normal motion compensation, ISAR imaging with the EM model, and ISAR imaging with GPS data are studied, with emphasis on GPS-aided imaging. As motion plays a critical role in ISAR, we study how the motion compensation should be done to focus the echoed data into a 2-D image. Besides the normal motion compensation, which uses the data sets themselves, here GPS-aided motion compensation is proposed and studied in detail, which uses GPS motion data of the aircraft as an additional input. Comparison of these two cases helps to expose problems of the normal motion compensation and to form a better understanding of ISAR imaging process. EM model-based imaging results can be regarded as a third reference for the comparison. Neither GPS-aided imaging nor comparison between it and normal motion compensation imaging or EM model-based imaging has been reported, therefore this work is both initiative and difficult in this sense. After giving problem definition and objectives of the project, this final report presents the underlying theory of ISAR imaging.