強健式寬頻陣列多重波束成型技術

Abstract

在陣列信號處理中，有關於Narrowband的信號的理論已經非常完整，對於各種非理想狀況會產生的效應也都能經由適當的Robust演算法將非理想效應修正到一個可以接受的程度。本論文嘗試用以往在Narrowband的陣列信號處理的技術來用在Broadband的陣列信號處理中，使用的信號是寬頻，使用的天線陣列也是用tap-delay-line的方式來產生想要的頻率響應。 在本文中探討兩種非理想效應:角度誤判、同調信號干擾。並且嘗試去利用以往在Narrowband的Robust演算法延展到Broadband的架構上，並且模擬他的performance。 對於角度誤判，我延續了之前學長的研究用限制目標函數梯度法配合雜訊子空間投影法(Cheng)方法來修正。在這裡會有尋找信號子空間的問題，以往利用Eigen-value Decomposition(EVD)來尋找信號子空間的方法將會因為寬頻的信號以及tap-delay-line的架構而產生問題，而我們自己找一套方法來取代之前的作法。 對於同調信號干擾的問題，我延續了在Narrowband裡的二級天線陣列的研究，將它變成Broadband的架構，並且拿它與Spatial Smoothing做個比較。

The theory about narrowband array signal processing is almost complete and saturated. There exist lots of robust algorithms for each non-ideal condition to improve the array performance. In my thesis I try to extend the robust algorithm used in narrowband signal and narrowband beamformer to broadband beamformer dealing with broadband signals. And in the broadband beamformer structure I use the tap-delay-line after each array element to yield desired frequency response. I discuss two non-ideal situations: angle mismatch and coherent interference. Then under the criterions used in narrowband case before, I extend the robust algorithm to broadband case and simulate their performance. For angle mismatch, I extend the Cheng’s method to broadband case. However finding the signal subspace is not easy like narrowband case because the broad frequency band and the tap-delay-line structure. So I develop a method to construct the signal subspace. For coherent interference I extend the two stage array structure in narrowband case to broadband case, and compare its performance with spatial smoothing.