Research On Wide-Area Distributed Array Beamforming Technology

Wide-area distributed array is a large-aperture array composed of a small number of array elements.Owing to the advantages of strong flexibility,high angular resolution,good maneuverability and strong scalability,wide-area distributed array has broad application prospects in radar detection,satellite positioning and wireless communication,etc.However,the structural characteristics of multiple elements,sparse distribution,and large aperture will lead to unsuppressed grating lobes and near-field targets.These problems make traditional far-field beamforming algorithms not applicable in wide-area distributed arrays.To solve the above critical issues,this thesis investigates wide-area distributed array beamforming technology.Novel techniques for grating lobe suppression and beamforming algorithms are proposed.The contribution is summarized as follows:1.On the problem of wide-area distributed arrays grating lobes,a novel grating lobes suppression algorithm based on dual-frequency frequency difference is proposed,which transmits two signals of different frequencies simultaneously,and uses the frequency difference between the two frequency points to ensure that grating lobes-free in the field of view,overcoming the flaws of the existing grating lobes suppression techniques such as high sidelobe levels,small field of view and high complexity of the algorithm;it is theoretically proved that the proposed algorithm can achieve grating lobes-free arrays with arbitrary element spacing without elevating sidelobe levels.The average beampattern properties including 3 d B beamwidth,peak and zero points of the sidelobe,3 d B sidelobe region,and average directivity are derived to evaluate the performance of the proposed algorithm.The concept of combining efficiency is proposed,and as a powerful tool to design a requirement on system synchronization.The thesis r proves that dual-frequency algorithm requires less synchronization error under the same synthesis efficiency,which lays a theoretical foundation for the realization of wide-area distributed array beamforming algorithm.2.On the problem of near-field non-blind beamforming,a novel near-field beamforming algorithm based on pulse alignment is proposed.The proposed algorithm firstly compresses the received signals of the array in a distance-to-pulse direction and realizes pulse alignment,and then performs distance-angle two-dimensional scanning for beamforming.The pulse compression is used to solve the problem of SNR loss caused by pulse misalignment in existing near-field beamforming,and the beamforming performance is thus improved effectively.In order to reduce the performance of beamforming due to the small number of quick beats in a single distance gate after pulse compression,diagonal loading technique is introduced to improve the robustness of the proposed algorithm.3.On the problem of near-field blind beamforming for wide-area distributed array,a near-SCORE approach based on cyclostationarity is proposed.The proposed approach exploits the difference of cyclic frequency among the desired signal,the interference and noise to suppress interference and noise without a priori information,which effectively improves the array gain.To address the problem of high sidelobe levels of the near-SCORE approach,a sidelobe suppression for blind beamforming is proposed.In this technique,the sparse constraint of the non-blind beamforming is extended to near-field blind beamforming and sidelobes is suppressed effectively.In addition,the corresponding iterative formulas and the non-iterative suboptimal solution with L₂ norm criterion are given in the thesis.