Research On Time-varying Beam Tracking Technologies For Frequency Diverse Array Radar

Frequency Diverse Array(FDA)radar is an emerging array radar technology proposed in recent years.On the basis of the traditional phased array(PA)radar,FDA radar realizes the j ointly range-angle-dependent characteristics,time-varying characteristics and automatic scanning characteristics of the transmitted beam by adding a frequency offset much smaller than the carrier frequency to each array element.Hence,compared with the beam characteristics of PA radar,FDA radar time-varying beam has more extensive application potential and higher signal processing technical requirements in the fields of range-azimuth joint estimation,target detection and location,spatial interference/clutter covariance matrix estimation,electronic countermeasure and secure communication.Aiming at the time-varying beam characteristics of FDA radar,this thesis has system-atically investigated the critical techniques associated with time-varying beam tracking departing from the fundamental signal characteristics of FDA radar,including FDA radar transmitting beampattern synthesis and optimization,time-varying beam tracking algo-rithm and receiver design for time-varying FDA signal.The main research contributions of this thesis are summarized as follows.(1)Synthesis optimization and theoretical analysis for time-varying transmitting beam-pattern of the pulsed-FDA radar.This thesis systematically analyses the influence of frequency offset on time-varying transmitting beampattern and researches the automatic scanning characteristics of FDA transmitting beampattern in range and angle dimension.In order to solve the range-angle coupling characteristic and suppress the time-varying characteristic,this thesis constructs the method for controlling the scanning region of the main beam as the solution of frequency offset optimization problem and proposes a trans-mitting beampattern optimization method which uses the genetic algorithm(GA)to iteratively update and solve the non-convex optimization problem.Besides,this thesis compares the transmitting beampattern under the condition of frequency offset with different function growth(logarithmic function,square function,linear function)and analyses the influence of frequency offset on the main beam scanning region.Taking long pulse,short pulse and pulse burst as examples,this thesis investigates the energy focusing problem of time-varying beampattern when a certain beam energy attenuation is allowed,which is a theoretical foundation and practical premise for target detection and location of the pulsed-FDA radar.(2)Direction of arrival(DOA)tracking algorithm using FDA radar time-varying beam.For frequency diverse array multi-input and multi-output(FDA-MIMO)radar,this thesis derives the mathematical model of ambiguity function,which is used to sample the time-varying beam information in real time instead of autocorrelation function.Combin-ing projection approximation subspace tracking with deflation(PASTd)with the DOA estimation of FDA signals,this thesis proposes an optimized estimating signal parame-ter via rotational invariance techniques(ESPRIT)algorithm for DOA tracking of mov-ing targets,which effectively solves the range-angle coupling characteristics of the time-varying beams and simplifies the computational complexity by using ambiguity function and PASTd algorithm.Compared with the traditional ESPRIT algorithm and projection approximation subspace tracking(PAST)algorithm,the numerical results verify the ef-fectiveness of the algorithm for time-varying beam tracking.In the research of limited sampling snapshot number and spatial spectrum estimation with dynamic statistical char-acteristics,the part of this thesis establishes a scientific basis for FDA radar beam tracking theory.(3)The general receiver data model for the time-varying beam of FDA radar under interference environment.Focusing on the time-varying characteristics of FDA beam,this thesis deduces the sufficient statistics of the general receiver data under interference en-vironment and designs the multi-channel receiver structure.According to the difference of the transmission covariance matrix,this thesis deduces the coherent waveforms FDA radar model and the orthogonal waveform FDA radar model and analyses the noise components.Based on the proposed model,the performance of FDA radars and traditional radars including PA and MIMO radars are comprehensively compared from the aspects of output signal-to-interference plus noise ratio(SINR),array sensitivity and Cramer-Rao Bound(CRB)performance.The simulation results show that the model achieves better performance than traditional radar in parameter estimation and target detection under strong interference environment and the application advantages of FDA radar in the inter-ference suppression and multi-dimensional target detection.