Research On ISAR Imaging Method For Targets With Complex Motion

Inverse Synthetic Aperture Radar(ISAR), like the Synthetic Aperture Radar(SAR) is a kind of active microwave imaging radar system. It is aimed at to space and air moving target imaging, and is one of the important developing direction of imaging radar. For imaging of targets with complex motions(high speed, spinning, non-uniform rotation, precession, etc.) using the traditional Range Doppler(RD) imaging algorithm, even the Range-Instantaneous-Doppler(RID) algorithms, cannot get high-quality ISAR. Study of imaging algorithm for complicated dynamic targets is desired. Through analyzing the echo signal characteristics of high dynamic targets, developing feasible imaging methods for complex moving targets is of great importance for identification and recognition of space or air targets.This thesis is devoted to studying the ISAR imaging method for high dynamic targets. General form of echo signals for high dynamic moving targets is deduced. Based on the linear frequency modulation signal and existing algorithms, pulse compression processing is described to achieve high range resolution. At the meantime, a real cone-like target model is employed to generate the target scattering signals by using the computational electromagnetics software, and then using the simulated echo signals to produce the ISAR imaging. It shows that, by comparison of the model and the image, the imaging processing presented in the present thesis possess preliminary engineering application values.The main points of this thesis are as follows:1. High dynamic target imaging mathematical modelBasic principle of ISAR imaging is described. Key techniques for non-cooperative target ISAR imaging are reviewed. According to the common process of numerical simulation, general form of radar echo signals from high speed and complex rotating targets are characterized.2. High dynamic target echo signal processing algorithmsMain influencing factors of the complex motions on ISAR imaging are analyzed, including the range walking and bending effects. Improved Range-Doppler Algorithm(RDA) is discussed, which is suitable for high dynamic targets. Applying the improved imaging algorithm to high speed moving target based on broadband simulation data and measured data are explored. The results show that the improved method is workable.3. High dynamic target electromagnetic simulation imagingModeling and meshing by using the CATIA software and the HYPERMESH software for a warhead model is conducted. Then the FEKO software that is incorporated with the high efficient multilevel fast multipole algorithm(MLFMA) is employed to calculate the stationary backscattering properties at 5.85 GHz. The stationary backscattering data are transformed to moving case by using the relativistic transforms for space-time and electromagnetic fields. Doppler parameter caused by hypersonic translation and micro-Doppler parameters due to rotating motions are extracted.