| Multiple input multiple output(MIMO)radar is a new type of radar.MIMO radar's transmitting and receiving beams are synthesized simultaneously to make the angle measurement more accurate.Moreover,MIMO radar has longer residence time for omnidirectional beam in orthogonal mode and multi beams in partially correlated mode,which offers greater sensitivity to detecting slowly moving targets with more pulses.Waveform optimization is also a unique ability of MIMO radar.It allows the emission energy to be uniformly distributed in space or concentrated in the angle of interest,and a small portion of transmitted energy is distributed in some directions with a null in these directions.The flexibility of the transmit beam pattern design enables the MIMO radar to adapt to the complex and variable environment and make rational use of transmitting resources.This thesis mainly studies the waveform design problems of MIMO radar,and the specific contents are as follows:In this thesis,at first,we establish the MIMO radar linear array model.Based on this,the MIMO radar transmit-receive principle and two signal processing paths are introduced.Then we introduce the concepts of radar transmit beam pattern,spatial synthetic correlation function,Doppler tolerance and other related concepts,which play a guiding role in radar waveform design.Waveform design is organized as follows.The third chapter focuses on orthogonal waveform: orthogonal phase coding waveforms and orthogonal LFM signal waveforms,we compare the properties of their spatial synthetic autocorrelation function and Doppler tolerance.And the actual engineering application of two orthogonal waveforms is given respectively.Secondly,the partial correlation phase coding signal waveform and the partial correlation LFM signal waveform are studied in the fourth chapter.The design of phase coding signal waveform mainly uses step-by-step method.The semi-definite Quadratic Programming(SQP)and the basic beam method are used to optimize the covariance matrix of the transmitted waveform respectively.The computational complexity of the two methods is compared,whose matching degree of the pattern of the covariance matrix is also evaluated.When the transmit waveforms are designed,their performance are compared by using Cyclic algorithm(CA)and sequential quadratic programming,respectively.In the aspect of LFM signal waveform,the factors affecting its emission pattern are obtained by analyzing the emission pattern of the LFM signal.Aiming at the problem of broadening the main response of the spatial synthetic autocorrelation function of the existing partially correlated LFM signal,a new method is proposed,which has good pulse compression performance.Finally,the fifth chapter studies the design of MIMO radar nulls-setting waveform.A design method of phase coding nulls-setting waveform is reviewed,and then a method for designing the LFM signal nulls-setting waveform is proposed.The method takes the nulls-setting constraint as the criterion,and optimizes the frequency interval and initial phase of the LFM signal.The designed waveform has ideal nulls-setting effect and pulse compression performance. |
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