場型分集之雙極化可調式天線

Abstract

本論文主要探討一個具有雙極化及場型分集之可調式天線系統，應用於室內無線區域網路傳輸裝置之設計，適用於IEEE 802.11a的頻段。首先我們分別提出了兩種天線的設計，第一種為雙極化環狀槽孔天線用來產生正向輻射的場型；第二種為微帶天線在中心饋入用來激發TM_01模態產生錐形輻射的場型，由於考慮天線會整合在一起，兩種天線在設計時擁有同樣的天線尺寸(〖50×50×7.6mm〗^3)，包括6mm高的空氣層以及兩層厚度為0.8mm的FR4介質板(介電常數為4.4)，饋入上也同樣使用電容性耦合的方式。此外為了減少天線整合後對匹配的影響，兩種天線調整匹配用的參數在設計時也盡量使其互相獨立。 兩種天線整合之後，首先我們提出假設並試著利用可變電容的調變來微調錐形輻射場型的角度涵蓋範圍，使訊號有更多的調變空間，比較完模擬與量測並選擇最佳的電容值後，我們再利用射頻電路用的開關晶片來切換場型與極化。本論文將提出設計的過程以及方法，天線的參數分析及模擬與量測的比較。 最後在實作與量測的部分，為了了解開關晶片、可變電容對天線匹配與輻射特性造成的影響，本論文在實作上因應饋入方式的不同，提出三種天線版本:第一種使用垂直饋入SMA接頭，第二種實裝可變電容，而第三種是實裝開關電路，針對開關電路我們也利用了一背對背(back to back)的開關測試用電路來進行校準。

This thesis presents a reconfigurable antenna with dual polarization and pattern diversity for indoor wireless transmission applications. First, two kinds of antennas are proposed in this thesis. One is a dual-polarized ring slot antenna, which generates broadside radiation patterns. The other is a monopole antenna, which generates conical radiation patterns. In view of the co-located design, both antennas are integrated in the same antenna module (〖50×50×7.6mm〗^3), including a 6mm high air layer between two layers of FR4 substrate (of thickness 0.8mm and permittivity 4.4). Both antennas are fed by the capacitively coupled feeds. In addition, to reduce the impact on the matching after integration, we proposed some parameters for adjusting impedance matching, independently from each other. After integrating two antennas, we use varactor to fine tune the direction of maximum radiation and further extend the adaptive range of radiation patterns. After choosing optimal capacitance value, we use RF switch to change different polarizations and radiation patterns. Lastly, we built three prototypes (integrated with SMA connector, varactor and switch), and a back-to-back test circuit to calibrate the effects of switch.