Efficient method for imaging non-uniform rotating targets

In the inverse synthetic aperture radar (ISAR) imaging, the image will be greatly degraded by the non-uniform rotation of the target. To address this issue, an efficient method for ISAR imaging is proposed. In the proposed method, a time frequency analysis is firstly made of single range unit cross-range echo data. Secondly, according to the relationship between the rotating speed and the scaling factor, the reference signal is constructed by scaling the frequency distribution of the middle time with many different scaling factors. Thirdly, the curve of the rotating speed is estimated by figuring out the correlation coefficient between the reference signal and the frequency distribution of other moments. Then, an interpolation is executed in azimuth to compensate for the effects of changes in rotation speed. Finally, the well focused ISAR image of the target is obtained. Since all the changes of the target rotating speed are exactly estimated and compensated, the proposed approach is applicable to all the targets however the rotating speed changes. Moreover, it is computationally efficient and can be used in real time processing. Simulation results and measured data are provided to confirm the validity of the proposed approach.