Frequency Stepped SAR/ISAR Imaging Based On Bandwidth Synthesis

Synthetic Aperture Radar (SAR) is a kind of radar with high resolution, which can produce two-dimensional high-resolution images of targets from a long distance day and night and in all weather conditions, therefore it is widely used. Since the demands of application are improved continuously, the demands of resolution have been higher and higher. Because range resolution of radar is inversely proportional to the bandwidth of signal, signal with big bandwidth is needed to obtain high range resolution. However, the increase of instantaneous bandwidth will definitely lead to the higher demands of hardware system. Frequency stepped signal can not only realize high range resolution but also reduce the demands of instantaneous bandwidth and the sample rate of radar system and modulated frequency stepped signals can be combined to one single signal with high bandwidth by using synthetic bandwidth methods, so synthetic bandwidth methods have become extensively utilized approaches.In this paper the imaging theory of frequency stepped signal is described firstly, time domain synthetic bandwidth methods and frequency domain bandwidth methods are briefly introduced, the flow chart using synthetic bandwidth method and result of the measured data are given. That motion error and time delay of echo signal must be considered before applying the available synthetic bandwidth methods in actual SAR imaging is discussed. And then a method is proposed, in which motion compensation and compensation in Doppler domain are integrated with time domain synthetic bandwidth method in order to get high quality SAR image. The algorithm flow chart and the result of measured data are provided. Secondly frequency stepped ISAR imaging of high speed target is analyzed and simulated. At last a cohering method of ISAR data is proposed. The formulas are deduced and some measured data are processed to verify the proposed approach.