Analysis And Research Of Transient Electromagnetic Scattering Moving Target ISAR Imaging Algorithm

Inverse synthetic aperture radar (ISAR) is applicative when the radar is stationary and the target is in unknown motion. It has been widely applied for the identification and classification of targets for military purpose. This thesis mainly studies the time domain high frequency method for simulation of the ISAR echo signals from arbitrarily moving targets and their corresponding ISAR imaging algorithms, including the traditional range Doppler algorithm for smoothly moving targets and the range instantaneous Doppler algorithm for maneuvering targets. This thesis mainly includes the following contents:Firstly, the frame hopping method is adopted to precisely analyze the transient electromagnetic scattering of uniformly moving target. The correctness of the algorithm is proved via the theory of Doppler effects in the section of numerical results. Then, combining with the quasi-stationary method, the accurate ISAR echo signal for moving targets can be obtained for the study of ISAR imaging algorithms. Secondly, the influence on ISAR signals caused by targets motion is analyzed. The moving targets are divided into smoothly moving targets and maneuvering targets. Based on the analysis of ISAR echo signals, the traditional range Doppler imaging algorithm applied for smoothly moving targets is addressed, including the implementation of range alignment and motion compensation. According to the simulated results, the implementation of the range Doppler imaging algorithm is verified to be correct. Thirdly, the imaging algorithms of maneuvering targets are studied. Among the common ISAR imaging algorithms of maneuvering targets, the range instantaneous Doppler imaging algorithm based on joint time-frequency distribution is proved to have a better performance, which is focused on in the thesis. Clearly, the performance of this algorithm depends on the performance of the used time-frequency distribution method. Therefore, some common time-frequency distribution methods are studied, including the short-time Fourier transform, the Wigner-Ville distribution, the smoothed pseudo Wigner-Ville distribution, the Choi-William distribution, the reassigned spectrogram and the reassigned smoothed pseudo Wigner-Ville distribution. According to the simulated and measured results, the reassigned spectrogram is quantitatively proved to have the highest resolution in time and frequency domain. So the highest quality image can be obtained based on this method. Unfortunately, this method is computationally expensive. In order to reduce the heavy computation cost, a recursive method is introduced in the reassigned spectrogram algorithm. The proposed method can reduce the computation time without sacrificing the readability of image, especially for long signals.