可塑性雙頻四極化掃描天線之設計

Abstract

此論文的研究方向著重於雙頻L形電容耦合饋入式平面天線搭配上運用奇偶模分析方式設計出的雙頻枝幹耦合器與寬頻的切換電路的設計來達成雙頻四極化的目的。此架構操作的頻率是WiMAX (3.5GHz)與WiFi (2.45GHz)的頻段，其中WiMAX更是時下熱門的應用，它相較於WiFi有較遠的傳輸距離、較寬的頻帶與較高的傳輸速度，這些都足以應付商業上對於傳輸資料量相對增大的多媒體資訊的需求。 極化掃描天線對於無線傳輸的優點是能透過多重極化提供更多的通訊通道增加了資料的承載量與接收端的敏感度，更較能減低多重散射環境對於訊號品質的影響。本論文也將依循著這個原則設計出能產生雙圓形與雙線性的天線架構。整體架構包含三個部分：L形電容耦合饋入式平面天線是為了克服平面式微帶天線窄頻的缺點；雙頻枝幹耦合器提供天線在操作的兩個頻率點上各輸出兩組相差正九十度與負九十度的訊號，最後寬頻的切換電路是將枝幹耦合器的兩組訊號作分配用以激發不同方向的天線以產生線性極化模態或同時激發兩個垂直的天線以產生圓形極化模態。

This thesis introduces the design of a patch antenna fed by L-shaped capacitive coupling probes, along with a dual-band branch line coupler designed by the even-odd mode analysis method we proposed in this thesis and the wideband switching circuit to achieve our purpose of the dual-band quadri-polarization diversity antenna. In nowadays, WiMAX is becoming more popular in wireless communication application besides WiFi. This antenna structure operates at WiFi (2.45GHz) and WiMAX (3.5GHz) spectrum. The transmission distance, bandwidth and transmission speed of WiMAX operation are better than that of WiFi The advantages of polarization diversity antenna include providing more channels by producing more polarization modes to enhance the capacity and receiver sensitivity and reducing the effect of multi-scattering environment. Based on these principles, we propose an antenna structure which can produce dual linear and dual circular polarizations. There are three parts in our design: first, the dual-band branch line coupler provides two equal-power signals with 90° or -90° phase difference in each operating band. Second, the wideband switching circuit controls the two output powers of branch line coupler to excite the antenna structure for producing linear polarization wave or circular polarization wave. Third, the L-shaped fed conventional planar patch antenna is provided to overcome the coupling effect.