Application Of Frequency Diverse Array Radar Time-varying And Covariance Estimation

Unlike traditional Phase Array(PA)radar,Frequency Diverse Array(FDA)radar introduces a small frequency increment into each transmitting element.Due to the exis-tence of frequency increment,the beampattern of FDA radar is completely different from that of PA radar.Specifically,the beampattern of FDA radar is range-angle-dependent,range-angle-coupled and even time-varying,which means the beampattern within a pulse time no longer points to a specific and constant angle,instead,there is a ”twist” within a certain angle.Hence,the FDA radar has great potential application in the following aspects: transmitting array beampattern synthesis,target detection and parameter estima-tion,range-dependent clutter and interference suppression,radio frequency(RF)stealth and adaptive processing.Based on the analysis of the structure and signal characteristics of FDA radar,this dissertation focuses on the analysis and research in the following areas:the time-varying beampattern of the FDA radar,covariance matrix estimation algorithm,interference suppression and target parameter estimation based on covariance matrix up-date,fast target search and adaptive target tracking based on airspace dichotomy.The main work and innovations are summarized as follows:1.Time-varying property of FDA transmit beampattern.Aiming at the time-varying property of FDA beampattern,the concept of signal-to-noise instantaneous power ratio is firstly introduced,and then the reconnaissance of FDA radar signal is carried out through the sum-difference beam algorithm,the phase interference algorithm,the Time Difference of Arrival(TDOA)and the Frequency Difference of Arrival(FDOA)algorithm,respec-tively.Then,the equiphase surface characteristic of the FDA radar is analyzed,and the Cramér-Rao bound of signal reconnaissance is derived.For the FDA transmit signal re-connaissance on the basis of TDOA and FDOA,the mutual ambiguity function of the received signal is analyzed,and the Cramér-Rao bound of TDOA and FDOA is also de-rived.Finally,it illustrates that the performance of FDA radar is superior to PA radar in low probability of intercept.2.Covariance matrix structure of the FDA radar and its estimation algorithm.The coupled range-angle and even time-varying beampattern of FDA radar brings difficulty in estimating the covariance matrix,which makes the estimation methods of the PA radar cannot be applicable.In the light of time-varying FDA beampattern within a single pulse,the receiver model of the FDA radar which owns the transmitting characteristics of multi-carrier and multi-frequency is firstly analyzed.Then,based on the receiver model,the covariance matrix structures of correlated FDA radar and orthogonal FDA radar are de-duced,respectively.In addition,due to the range-angle-coupling of the beampattern,FDA radar cannot directly exploit the returned signal of the adjacent range units to estimate the covariance matrix,and there will be a more severe reduction in the number of samples.To this end,this dissertation proposes shrinkage-to-tapering algorithm and shrinkage-to-Toeplitz rectification algorithm to estimate the covariance matrix of orthogonal FDA radar,and structured approximate maximum likelihood estimation algorithm to estimate the co-variance matrix of coherent FDA radar.3.FDA-MIMO(Multi-Input and Multi-Output)radar interference suppression and target parameters estimation based on covariance matrix update.Firstly,for the spectrum interference signal,the covariance matrix structure of the spectrum interference signal of the FDA radar is analyzed.An adaptive transmitting element power allocation method depended on covariance matrix update for FDA MIMO radar,which utilizes the maxi-mum Signal to Interference plus Noise Ratio(SINR)criterion,is proposed for spectrum interference suppression.Since FDA radar has the transmitting characteristics of multi-carrier and multi-frequency,the frequency spectrum can be flexibly adjusted by changing the power distribution of the transmitting array elements.Therefore,the adaptive trans-mitting array element power allocation method proposed in this dissertation can achieve narrowband spectrum interference suppression with low computational complexity.Sec-ondly,in the view of the range-angle-dependent and range-angle-coupling beampattern of the FDA radar,the FDA MIMO radar is used to realize beampattern decoupling,and a joint two-dimensional range and angle estimation of the target based on covariance matrix update is presented.4.Fast target search and adaptive tracking for the FDA radar.Consider that the beampattern of the FDA radar is range-angle-dependent and time-varying,and the “dis-tortion”of the beampattern is caused by the frequency increment,the initial scanning angle of the beampattern is related to the transmitting weight vector.This dissertation analyzes the automatic scanning characteristics of the FDA radar,and proposes a method based on airspace dichotomy to achieve rapid target search,which can flexibly convert the scanning range of the beampattern by adjusting the transmitting frequency offset and transmitting array weight vector.Compared with the scanning from all angles successively in PA radar,the airspace dichotomy algorithm has a faster scanning speed.Furthermore,the adaptive tracking of the target for the FDA radar is achieved with the covariance matrix update,the spectrum interference suppression algorithm,together with the Kalman filter.