Research On Some Key Problems Of Signal Processing Of Airborne Distributed Conformal Array Radar

With the increasing demand of aircraft platform for stealth,intelligence and omni-directional perception,airborne radar also develops from a single planar array with traditional nose to a skinned distributed conformal array with "random" layout.With the characteristics of high detection capacity,high detection precision,wide search angle,good stealth performance,and flexible working mode etc.,airborne distributed conformal array radar is an important technical direction of airborne radar development in the future.However,there are still many key problems to be solved in airborne distributed conformal array radar.Firstly,it is difficult to realize uniform array layout for irregular airborne platform distributed array.Meanwhile,the small platform greatly limits the degree of spatial freedom,which will greatly affect the realization of multi-dimensional parameter high-precision estimation of targets.Secondly,the flow pattern of airborne conformal array will cause the clutter distance correlation problem.In addition to the highly non-uniform clutter environment that airborne radar often faces,such problems above will lead to the difficulty in satisfying the independent and iden-distributed clutter training samples required for clutter covariance matrix estimation when space-time adaptive signal processing(STAP)is adopted.In conclusion,high precision estimation of multi-dimensional parameters and STAP processing for airborne distributed conformation array radar have become urgent problems to be solved.Thus,this paper focuses on several key problems of multi-dimensional parameter high-precision estimation and conformal array STAP processing under non-uniform array of airborne radar,and carries out theoretical research and experimental verification,which have important theoretical significance and application value.The main work carried out in this paper is summarized as follows:1)Such problems as limited spatial freedom of airborne distributed conformation array radar,difficulty in uniform array,etc.,which affect the performance of multi-dimensional parameter estimation and the complexity of the system and the large amount of computation,are studied.First of all,a multi-target angle-polarium-frequency joint estimation algorithm based on space-time nested sampling and linear operator is proposed.The algorithm used the RCS diversity of multiple CPI to construct a virtual polarity-space-time array manifold to realize the extension of degrees of freedom.Also,the method of subspace estimation using linear operator is derived.Finally,the idea of ESPRIT is adopted to estimate the angle,polarization and Doppler frequency of the target.The performance of parameter estimation can be significantly improved by constructing nested sampling.Secondly,a multi-objective angular-frequency joint estimation algorithm based on space-time nested sampling and one-bit quantization is proposed.It is confirmed that when the SNR is not very high,the one-bit array correlation matrix has the same characteristic structure as the non-quantized array correlation matrix.Therefore,the traditional non-quantization array parameter estimation algorithm can be used for the one-bit quantization array parameter estimation.The algorithm also improves the joint estimation precision of target parameters by using nested sampling,and reduces the complexity of sampling,transmission and storage by using one-bit quantization structure.2)It is difficult for the independent identically distributed clutter samples required by the STAP method,which meets the problems of the highly non-uniform clutter environment and the non-stationary clutter caused by the conformal array.In this paper,a sparse STAP method based on greedy iteration algorithm is proposed.It can reduce the requirement of independent identically distributed clutter samples.Based on this,an improved greedy iterative algorithm,Expanded Subspace Pursuit(ESP)algorithm,is proposed,which does not need to know the prior information of sparsity,and has good reconstruction performance and low computational complexity.Finally,the sparse recovery performance of STAP algorithm which based on ESP algorithm is verified by Multi-Channel Airborne Radar Measurements(MCARM)data.The results show that this algorithm has good performance of space-time spectrum reconstruction,good space-time two-dimensional frequency response and improvement factor.3)In order to solve the clutter range correlation problem caused by flow pattern of airborne conformal radar array,a two-stage compensation algorithm is proposed.This algorithm first compensated the main clutter by using doppler frequency shift compensation(ADC)compensation algorithm,and then gave the secondary compensation using the modified derivative update(MDBU)compensation algorithm.This algorithm can effectively solve the problem caused by clutter range correlation of conformal array.Its performance is better than the traditional compensation algorithm.Finally,the scheme of first airborne conformal array radar engineering prototype and outfield flight test were designed,and the engineering application STAP algorithm of airborne single-plane conformal array was verified through flight test,which laid a technical foundation for subsequent single-plane conformal array and even distributed conformal array STAP engineering application.