四埠雙極化自我雙工天線於無線區域網路MIMO之應用

Abstract

本論文主要探討一具有雙極化功能的四埠自我雙工天線，其操作於無線區域網路2.4~2.5GHz以及5~6GHz頻帶，並利用極化分集之設計，以及去耦合縫隙設計，將多天線系統整合至一小面積之內。由於多輸入多輸出( MIMO )系統在一小面積下，需容納多根天線架構，且須同時保持各埠天線的輻射特性，因此於天線間的去耦合架構設計，為設計重點之一；我們於低頻埠間設計一操作於2.45GHz四分之一有效波長的開路縫隙，使低頻的耦合電流於其上共振，於高頻埠間亦設計一操作於5.5GHz四分之一有效波長的開路縫隙，減少流至另一高頻埠的耦合電流。由於此天線架構是根據兩埠自我雙工天線[1]延伸而來的，因此基於該架構所分析的波導模態特性，在三層自我雙工天線仍然保有，故同極化下的高低頻埠，仍具有高低頻模態間的高隔離度特性。由於高頻時激發高頻埠，槽孔內的電場分布較無規則，故有部分的能量經由槽孔內之電場耦合至低頻埠，使得極化垂直的高低頻埠隔離度較差，因此我們在低頻埠饋入架構下，設計一操作於5.5GHz二分之一有效波長的孤立縫隙，阻隔高頻訊號流至低頻埠，進而提升兩極化垂直高低頻埠間的隔離度。因此，藉由兩埠自我雙工天線之模態分析，以及設計不同頻率有效長度的縫隙，可於操作頻帶下符合規格，即各埠之反射係數值皆小於-10dB，且埠與埠間的隔離度皆小於-15dB。本天線製作成本低、易與射頻電路整合組裝、並且已經達到分頻的功能，可應用於無線區域網路基地台之多輸入多輸出收發天線。

A dual-polarized self-diplexing antenna with four ports for WLAN application is proposed in this thesis. In general, accommodating multiple antennas in a small area and having low mutual coupling are very challenging in MIMO wireless systems. In this thesis, we can employ the polarization diversity and the de-coupling slot designs to achieve a 4-port dual-polarized dual-band MIMO antenna system. In the antenna structure, two opened slots are separately designed for 2.45GHz and 5.5GHz, which can block coupling current between ports operating at the same frequency. Furthermore, the proposed antenna is the extension structure of a two-port self-diplexing antenna, so the ports of the same polarization should have high mode-to-mode isolation based on the waveguide-mode analysis. Additionally, an isolated slot is added at the low-frequency ports to reduce high-frequency signals. Through the waveguide-mode analysis and different designs of the de-coupling slots, both the reflection coefficients of each port and isolation levels between two ports achieve promising performance. The proposed antenna is cost effective, easy to integrate with RF circuits, and dual-band/dual-polarized ready for the ports. It is suitable for the dual-band dual-polarized MIMO system for WLAN applications.