使用和/差技巧之適應陣列信號處理

Abstract

本篇論文提出一套用於雙生陣列天線之新適應性玻波束合成器 。吾人利 用振幅比較法與和差技巧，使用最小平方法求得在此架構下之最佳化波束 場型。利用差波束為－輔助波束將訊號源濾除，而和波束具有濾除干擾及 緩和訊號源消除效應之特性。在本篇論文中，吾人推導出和波束之輸出訊 號干擾雜訊比，並波束偏差對其之影響。為了補救波束偏差對通訊品質的 影響，吾人提出一些改良方法來增加系統對波束偏差之容忍度。除此，吾 人亦推導估測訊號源方向角之表示式及其二階分析。為了得到初步之訊號 源方向角，此論文亦提出方向角估測之反覆表示式。另一方面，在一變動 環境下，如何將干擾源濾除而得到準確訊號源位置，論文中亦推導出一遞 迴式來更新合成向量及訊號源之方向角。最後，吾人以電腦模擬的結果來 驗證以上所提出之結果。 We here present a new adaptive beamforming scheme for signal acquisition with an array consisting of doublets. The scheme is developed based on the amplitude-comparison/sum-and- difference technique employed in conventional monopulse radars. The optimum beamformer is constructed so as to minimize the mean-squared error in the difference-to-sum ratio. With the difference beam used as an auxiliary beam to suppress the desired signal, the resulting sum beam exhibits good interference cancellation capability and insignificant desired signal cancellation effect. Expression of the sum beamformer output signal-to-interference-plus-noise ratio is derived to analyze the effect of beam pointing error under various conditions. To remedy the performance degradation due to a large pointing error, we suggest some modified methods to further improve the robustness of the proposed beamformer. In addition, the closed-form expression for the estimate of the desired source direction is derived, and the corresponding second order analysis is given. We also present an iterative algorithm for preliminary acquisition of the desired source direction. For nonstationary environments, we derive a recursive algorithm for updating the optimum weight vectors and desired source direction given the array snapshot vectors. Numerical results are presented to demonstrate the efficacy of the proposed method.