A Study Of ISAR Technique For Target Discrimination In HF Radar

Because of the limited cross-range resolution, high frequency (HF) over-the-horizon (OTH) radar has the poor ability to determine the number of group targets and identify the large warship such as aircraft carrier in engineering applications. To improve this ability, a higher cross-range resolution is needed. An Inverse Synthetic Aperture Radar (ISAR) achieves high resolution in the cross-range dimension by taking advantage of the motion between radar and targets to synthesize the effect of a larger antenna aperture. Despite this ISAR signal processing method had been widely applied, it was rarely used in HF radar systems. In this paper, we probe into the application of the ISAR signal processing in HF radar systems elementarily.Because of the presence of the first-order sea echoes with dominant amplitude, the Doppler resolution technique which based on the range-velocity transformation is needed to extract the targets information in HF radar. Unlike the range-Doppler imaging in ISAR, this velocity transformation uses FFT without the motion compensation. So the ISAR signal processing may not be applied directly. Considering the target trace is required, the reasonable application scheme is summarized in the following. First, the range-velocity transformation and the target detection are finished, and estimate the range, velocity and azimuth of the detected targets for target tracking. Second, based on the estimation, the fine DBF is performed and the target spectra are filtered. Finally, the inverse velocity transformation and reverse weighting are done, and enough batches of signal are united. The united signal for the ISAR signal processing is called the cross-range dimension signal.The cross-range dimension signal of the target with nearly tangent motion is a linear frequency modulated signal. So the match-filter function may be constituted to realize the cross-range compress. Moreover, according to the ISAR signal processing, the nearly tangent motion may be equivalent to the rotated motion. Two methods of motion compensation may be applied. One is achieved by the estimated range information, the other one is the range alignment and the phase compensation. Phase compensation may be realized through estimating the...