Research On Radar Direction Finding Method Of Low Frequency MIMO Array

Low frequency multi input multi output(MIMO) radar is a hot research topic in the world of communication and radar field. Its working mode is transmitting multi-way irrelevant or orthogonal signal by the transmitter elements, receiving echo signal by the receiver elements and using matched filter for multi-way useful signal component recovering. This makes full use of space resources and significantly improves the performance of the radar. Array direction finding technology is an important research content in radar signal processing. At present, monopulse direction finding and super-resolution angle measuring algorithm are two common kinds of array direction finding methods.This thesis is focused on different forms of low frequency MIMO array radar, and different orthogonal signal models, studying and analyzing performance under ideal condition and the presence of amplitude and phase errors via monopulse algorithm and super-resolution angle measuring technique.Firstly, this thesis introduces the basic configuration of mono/bi-static MIMO radar, then elaborates two orthogonal signal models of the orthogonal LFM signal and quadrature phase code pulse signal in detail, briefly describing the structure of echo signal and signal models with the amplitude phase errors. This will provide solid theoretical foundation for the subsequent application of direction finding algorithm.Secondly, the sum and difference amplitude comparison monopulse angle measuring algorithm, direct phase comparison monopulse angle measuring algorithm, modified SSMUSIC super-resolution algorithm and TLS-ESPRIT super-resolution algorithm are studied in order. Mainly based on the mono/bi-static MIMO radar, different orthogonal signal models, and two conditions of ideal state and the presence of amplitude and phase errors, this thesis does a lot of comparing simulation analysis. At the same time, the relevant theory and the classical estimation methods of the estimation of singal source number are also analyzed, including an information theoretic criterion and Gail criterion, providing guarantee for super-resolution algorithm.Finally, from the point of practical engineering application view, a stationary platform receiving direction finding system is introduced. Setting a stationary transmission source and moving target, it locates the target via array antenna transmitting multiple pulse of orthogonal signal. The specific process is through the pulse compression to improve the signal-to-noise ratio with echo signal at first, then using simultaneous multi-beam formation technology to determine the target approximate position, and moving target detection(MTD) offset Doppler frequency shift between pulses by emission source, meanwhile accumulating multi pulses, then detecting target by Constant False Alarm Rate(CFAR) technique. As long as the target is detected, monopulse algorithm and super-resolution angle measuring technique will be used to estimate angle. Based on two types of structure of mono/bi-static MIMO radar, three kinds of measurement algorithm is applied to the receiving direction finding system, then the two cases of ideal state and the presence of amplitude and phase errors are compared to simulation and analysis.