ISAR Imaging Of Space Target Based On Scattering Models

Inverse synthetic aperture radar(ISAR) imaging of space target by simulating the electromagnetic(EM) echoes is able to provide motion parameters and structure features of the target, thus makes great contributions to target classification, recognition and so on. Although techniques for ISAR imaging have been fully developed, there still remains many problems due to the particularity of space target. In this dissertation, ISAR imaging of moving space target is studied in detail, mainly including the algorithm to calculate the multiple reflections of a target, the basic theory of ISAR imaging, Range Doppler(RD) algorithm, motion compensation(MOCOMP) technique of ISAR imaging. The main content of the dissertation is summarized as follows:This research begins with an introduction of the method calculating the Electromagnetic(EM) scattering of a target. Considering the specific structure of the target, a combinational method of geometrical optics and physical optics(GOPO) is presented, followed by a verification of both efficiency and feasibility by use of simple models, such as the dihedral and a combination composed by plate and cylinder. Based on this, a plane model is used to simulate for its scattering characteristic at different polarizations. Analyzing the results, there is almost no difference between two polarizations due to the PO algorithm which differs slightly for them. What’s more, we discuss detailly the influence of an antenna with angular structures, which can cause the multiple reflections, on the scattering of a satellite. Thus, a conclusion is drawn that the antenna with angular structures plays a dominant role in the scattering of the satellite at some specific anglesSecondly, the relationship between scattering field and imaging function is analyzed on the basis of ISAR imaging. And then, some imaging characteristics including the range profile, the cross-range profile and the ISAR images, are simulated for different parameters like bandwidth and sample points. In addition, in terms of the Range-Doppler imaging algorithm, two kinds of pulses signal are introduced and as well as the Doppler shifts in the cross-range. Meanwhile, the ISAR imaging simulations based on the algorithm using the stepped frequency signal are made and then discussed in detail. The results show that the antenna is such distinct that the conclusion before is further verified.Finally, in the ISAR imaging of moving targets, assuming that the target has only translational and rotational movements, there will be the Doppler effects, such as the Doppler blur and the range shift. Therefore, in order to solve the problems, the MOCOMP procedure has to be applied. For this, the Minimum Entropy method and the Joint Time-Frequency method are utilized to compensate the translation and rotation respectively. The obtained results show that, for the original images are so obscure and defocused that the target can hardly be distinguished. After the compensation of translation, it is just the Doppler blur left. As the rotational movement done, the target is clearly shown in the image. In a word, a moving target can be well imaged after the MOCOMP for the ISAR. At last, based on the simulated radar echoes, the ISAR imaging of satellite model in different parameters conditions is simulated. Analysis indicates that the distribution of scatters is clearer along range direction with the increasing bandwidth and more obvious along cross range direction with greater rotational velocity in the image.