Research On Joint Transmit And Receive Optimization Technology For Frequency Diverse Array Radar

Frequency diverse array(FDA)radar is a new radar system formed by imposing different frequency offsets(FOs)to each transmit array element of a conventional array radar.The existence of FO between the array elements makes the range information of different targets manifest not only in the delay of the envelope at the receiving side,but also in the difference of the phase between the array elements,thereby endowing the controllable design of freedom in the range dimension.Therefore,FDA radar not only has the functional characteristics of traditional array radars(including phased array and multiple-input multiple-output radars),but also has wider potential in the fields of range and angle joint positioning,mainlobe interference suppression,and radio frequency(RF)stealth.According to the size of the used FOs,FDA radar can be divided into coherent FDA radar with small FOs and FDA-MIMO radar with large FOs.Coherent FDA radar has the characteristics of high transmission gain and flexible design of beampattern,while FDA-MIMO radar has advantages in simplicity of reception and available degrees of freedom in waveform dimension.Starting from the signal characteristics of FDA radar,this dissertation systematically studies the joint transmit and receive optimization techniques of coherent FDA radar,FDA-MIMO radar,and robust FDA-MIMO radar.The main contributions and innovations are summarized as follows:(1)For the problem of coherent FDA beampattern synthesis,this dissertation models the FDA instantaneous transmit beampattern and the FDA integrated transmit beampattern on the basis of considering the time and range relationship.Then,taking the ratio of the power in the desired two-dimensional range-angle space to the power in the entire area as the target,a coherent FDA radar beampattern design scheme based on jointly optimizing transmit and receive weight vectors is formulated,subject to an energy constraint that limits the emitted energy of each transmit antenna and a similarity constraint such that a good transmit beampattern can be guaranteed.A sequential optimization method based on semidefinite relaxation(SDR)technique is developed to solve the resulting problem.(2)For the joint design of FDA-MIMO radar transmit waveform and receive weight vector in the context of signal-dependent mainlobe interference,two methods,the approximated alternating direction method of multipliers(P-ADMM)method and the majorizationminimization ADMM(MM-ADMM)method,are proposed in this dissertation to solve the resulting non-convex optimization problem with the maximization of signal to interference plus noise ratio(SINR)as the criterion and the inclusion of energy constraint,similarity constraint,and bandwidth constraint.The design freedom of FDA radar is fully utilized and the output SINR is greatly improved.(3)To address the problem of the reception complexity of coherent FDA radar and the low transmission gain of FDA-MIMO radar,a subarray structure with high transmission gain and simple reception is designed by dividing the array into overlapping subarrays in this dissertation.Subsequently,a joint optimization problem is further formulated for the subarray FDA radar transmit and receive weight vectors with the criterion of maximizing the output SINR when the azimuth angles of both the target and the interference are random variables.A consensus-ADMM algorithm is then proposed to solve the resulting problem.The convergence of the algorithm is analyzed,and some tips for initializing the variables and ways to speed up the implementation of the algorithm are given.(4)To address the robust design problem of FDA-MIMO radar in a spectrum-congested environment,the energy spectral density model of FDA-MIMO radar is modeled,and an iterative optimization algorithm based on SDR technique is proposed by means of joint design of transmit weight vector,transmit waveform,and receive weight vector,which flexibly achieves compatible operation of the FDA-MIMO radar and other services.(5)Considering the scenario with array amplitude and phase errors and insufficient a prior knowledge,a mismatched target steering vectors model is established based on norm model.Then,two algorithms based on CC-SDR(Charnes-Cooper transform combined with semidefinite SDR)and CD-DIN(Dinkelbach’s procedure embedded in a coordinate descent framework)are devised to jointly optimize the receive weight vector and the unimodular transmit waveform sequence,effectively utilizing the transmit power of the FDA-MIMO radar and improving the system robustness.