Research On MIMO Radar Target Detection Method In Multipath Environment

With the continuous development of the information age,the low-altitude ultra-low-altitude target gradually occupy an important position,which will have a great impact on public security.MIMO technology started from the field of communication.and was introduced into the field of wireless radar due to its many advantages in many aspects,which has quickly become a hot research topic.However,MIMO radar-based low-altitude ultra-low-altitude target detection technology is emerging,and the low-altitude detection will be affected by the multipath effect,resulting in the fluctuation of the received echo signal,and the detection performance of the radar will decline sharply.For the detection of low-altitude target,OFDM-MIMO radar has good detection performance.However,due to the orthogonality of signal frequency transmitted by OFDM-MIMO,some information will be lost,and its detection performance is difficult to get a qualitative improvement.Therefore,it is very important to find a new system radar for the research of low-altitude target under multi-path conditions.In addition,for the research of the new system radar,frequency diverse array(FDA)radar has been widely concerned by scholars because of its unique advantages.However,the research on FDA radar mainly focuses on waveform design,parameter estimation,clutter suppression,anti-jamming and target positioning.Therefore,it is of pioneering value to explore the target detection of FDA radar under multipath effect.Aiming at the above problems,this thesis established the MIMO radar with the FDA radar target detection model,and then to MIMO,phased array,and the FDA target under three different kinds of radar system were tested and the results are analyzed,finally combining MIMO radar with FDA,form a “new” radar system,The problem of target detection and the method of target detection are deeply explored in FDA-MIMO radar system.The main contents are summarized as follows:1.The system structure and target detection model of MIMO radar and FDA radar are introduced respectively,and the optimal likelihood ratio detection formula is derived based on Neyman-Pearson(NP)criterion.At the same time,the transmitting beam of FDA radar and phased array radar is analyzed and simulated respectively.Finally,the detection performance of MIMO radar,phased-array radar and FDA radar is compared,and the simulation results show that MIMO radar has unique advantages in target detection,followed by FDA radar.2.Aiming at the detection of low-altitude ultra-low-altitude target,there are mainly problems of target RCS scintillation and multipath effect,and a detection method based on FDA-MIMO radar for target is proposed.Combining FDA with MIMO radar,its frequency diversity and spatial diversity can not only overcome the flicker of target RCS,but also effectively suppress multipath interference.Firstly,a multipath FDA-MIMO radar target propagation model is established,and the total received signal was analyzed and simplified into a matrix form,which included the target radar scattering coefficient,doppler frequency and other information.Secondly,because there are unknown parameters in the real scene,the generalized likelihood ratio detection method is adopted to detect them.Finally,the simulation results show that the FDA-MIMO radar has better detection effect.3.In order to improve the detection performance of FDA-MIMO radar generalized likelihood ratio detection,the target detection algorithm and the FDA-MIMO radar emission waveform were optimized.Firstly,the method of two-threshold generalized likelihood ratio detection is adopted to further improve the detection probability,and the effectiveness of the method is verified by simulation.Then,based on the type of the transmitted pulse signal,the LFM signal is used to transmit the pulse signal,the echo signal is analyzed and its content is redefined,and the transmission form that can get more energy is derived.The simulation results show that this method can improve the detection performance of the target.Finally,three kinds of nonlinear increasing frequency offset are introduced based on the frequency offset types of FDA radar.Among them,square type and cubic type can make the width of the main lobe beam narrower,and the energy of the transmitted beam can be better concentrated.The simulation proves that the exponential type frequency deviation can improve the target detection performance more effectively.