Study Of Wideband Signal ISAR Imaging And Detection

ISAR imaging is a high-resolution radar imaging technique with small segment of viewing angle. The resolution in range is obtained by large bandwidth waveforms, and in cross-range by coherent integration of the return signals. ISAR theory and technique have seen great developments in the last two decades, and, it is gradually applied to practical systems. We set off our discussion and research work to the problem in wideband ISAR imaging and detection.In the process of ISAR imaging of a ship, which is driven by nonlinear forces from ocean waves, the swing exists in three dimensions. The principle of the dominant swing of a ship is similar to that of a pendulum. To deal with problems arise from ship ISAR imaging, method based on pendulum module is proposed. It is demonstrated that the phase history in each range bin of the high range resolution echoes from periodic moving scatter approximates to linear frequency modulation signal, which represents cross-range location. In some cases, better images can be obtained from linear frequency modulation components. Based on pendulum model, the three and higher order phase errors, which are caused by nonlinear phase history, can be compensated with rank two phase estimator and the improved rank one auto focus algorithms. Both the images from frequency components and linear frequency components can be obtained simultaneously by adopting the proposed method. Processing of real data demonstrated that the method presented in this dissertation is better than a traditional one because two complementary images can be obtained form complementary components and thus have a higher imaging probability but a traditional method can only extract one image form frequency component.Missile classification and identification with fake target interference is and essential problem in missile defense systems. Target imaging with ISAR technique is an efficient approach to this problem. The key of missile imaging with fake target interference lies in fact that the proper motion compensation must be applied to the desired target. Because of the interference effect between targets, compensation method based on reference point cannot be applied directly. In this dissertation, a method based on the improved keystone transform is proposed for dealing with the problem of linear range alignment elimination of missile target with fake target interference.Wideband signal is widely used in modern radar systems to obtain more fine range resolution. With wideband signal adopted, target scatters take up severaladjacent range resolution bins and become range extended target. Because of the present of weak scatters, the detector based on range energy accumulation has a poor performance. To eliminate drawbacks, weights should be given to range compressed echo according to relative scatter amplitude, which can be estimated form the detected probability because the locations of scatters stay unchanged within the adjacent tens of pulses. The benefit for range extended target detection with estimated weights has been discussed by numerical calculation.