Terahertz Radar Isar Imaging Technology Research

In recent years, with in-depth research of terhertz (THz) and development ofterhertz components, terhertz has aroused the attention of the world, especially indeveloped countries. The advantageous features of terahertz make it great applicationprospects in the area of inverse synthetic aperture (ISAR) imaging. The echo signals ofaircraft rotors are usually separated or suppressed as interfering signals in existingaircraft ISAR imaging methods, only to get the image of aircraft body. But withintroduction of the micro-Dopper concept and progression of micro-Dopper study, it isrecognized that the micro-Doppler phenomenon can be seen as the characteristics ofinteraction between rotating parts and the body. Micro-Doppler phenomenon canprovide us with some new information, such as targht geometric structure,electromagnetic properties, movement characteristics and so on. Therefore, usingmicro-Doppler information to get the ISAR images of the aircraft body and also aircraftrotors has become a new research direction.This dissertation studies the methods of Micro-Doppler analysis and parameterextraction, on this basis, focuses on the target ISAR imaging algorithm with rotatingparts. The main content of this dissertation is summarized as follows.(1)The phenomenon of micro-Doppler is researched. Firstly, a generalmethematical model of the micro-Dopper is established. Then we use time-frequencymethod to analysis micro-Doppler frequency of rotating targets and compare themicro-Doppler characteristics of different frequency bands. Finally, we use threedifferent methods, including the Wigner-Ville(W-V) distribution peak detection method,the First-order conditional moment method and the three-parameter sinusoidal Houghtransform method, to extract the mirco-Dopper parameters. The scope of applicationand noise immunity of each method is compared.(2)ISAR imaging algorithms of targets with rotating parts is researched. Firsrtly, ageometric model and a signal model of the targets with rotating parts are established.Then we analyze the different characteristics of body scattering points and rotating partsscattering points in the range-doppler domain image. Based on this, we use a sinusoidal Hough transform method to extract micro-Doppler information and to separate the echoof body scattering points and rotating parts scattering points. Next, R-D imagingalgorithm is used to the echo of body scattering points. And Inverse Radon transform isused to rotating parts scattering points, according to the theory that the high resolutionrange profile is the Radon transform of target distribution function. At last, we brieflyanalyze the resolution of the imaging algorithms.(3)Improvements of the above-mentioned imaging algorithms are discussed. Inview of some situation such as the offset of rotation center and the presence of noise,some improved methods are proposed and the feasibility of these methods are verfiedby simulation experiments.