可應用於雙頻多輸入多輸出天線之解耦合網路設計

Abstract

近年來由於網路終端用戶對於網路頻寬與傳輸速率的要求與日俱增，因此應用於MIMO系統的陣列天線越發普及，但緊密排列的陣列天線間之耦合效應，一直都是格外重要的議題。本篇論文將提出使用180度雙頻枝幹耦合器解耦合網路，來解決MIMO系統中的陣列天線相互耦合的問題。 在本論文中，我們提出的陣列天線解耦合系統，其本質為一180度雙頻分波耦合器，主要結構是由90度雙頻枝幹分波耦合器與90度寬頻位移器串接所組成。其目的在於，使雙埠陣列天線端產生正交特徵模態－奇模態與偶模態。因奇模態與偶模態本身會有獨立且不會相互耦合之特性。故此時我們可以預期，若解耦合網路可於奇偶模態下各埠口皆阻抗匹配，理想上陣列天線場型應會以相互正交呈現，達到場型分集目的。因此若可有效的激發奇偶模態訊號，等同於使此雙埠陣列天線達到解耦合之目的。本論文係透過一款緊密排列的陣列天線以充分驗證此概念之可行性。

For the past few years, there is an growing demand on the bandwidth and data-rate for internet end users. This leads to the need of closely spaced antenna array for MIMO applications. But, the strong mutual coupling between the array antennas in a narrow spacing could dramatically degrade the system capacity if the array spacing is less than . In this thesis, it is shown that this effect can be suppressed by the design of decoupling network. In this thesis, we proposed a 180 degree hybrid decoupling network which was composed of a 90 degree dual-band branch-line coupler and a 90 degree broadband phase shifter. Therefore, the orthogonal eigenmodes- odd mode and even mode will be realized base on 180 degree hybrid at the side of compact array antenna. Since the mode of odd and even will be independent and de-coupled with each other, we can expect that the radiation pattern of array antenna will be orthogonal if all the ports of decoupling network are matched. If we can excite the orthogonal modes effectively, the decoupling and pattern diversity of this antenna array are achieved. A compact dual-band array antenna is developed to validate the theories above.