應用於無線網路之新型雙頻開路諧振環單極天線之設計及量測

Abstract

本論文中，我們提出對於多頻天線新的設計方法。將常使用在平面式微波濾波器中常用到的二分之一波長開路諧振環的觀念，結合到共振型天線，使其有雙頻的效果。本論文所提出的天線架構是採用兩種不同且操作在不同頻率的共振機制彼此互相耦合，而使此天線在不同頻段同時匹配。此兩不同的共振機制分別為操作在低頻的二分之一波長開路諧振環、和操作在高頻的倒L型單極天線；靠著彼此的互相耦合，使得此新型的雙頻天線只需要一個餽入電路即可達到雙頻的目的。而此天線雖然是印製在印刷電路板上，但其尺寸不大，約13×10mm2。除此之外，本論文也對此雙頻天線做簡單的等效電路模型分析，以驗證開路環和倒L型單極天線間耦合強度對此天線的影響。經過模擬與實做在匹配頻寬上足夠給WLAN 802.11a/b/g使用，而輻射場型在每個頻率都近似全向性而最大平均增益都接近0dBi。 此外也針對便宜但製程參數不穩定的FR4板，做製程參數變動對天線敏感度的測試，可發現對此需要靠著耦合達到雙頻的天線影響不大。最後我們也進一步將此雙頻天線設計成分集式天線，藉由一些簡單但不佔據空間的屏障物來減低兩天線間的耦合效應。

In this thesis, we propose a novel design method for multi-band antenna. We utilize the concept of λ/2 open-loop resonator used in microwave filter frequently, and combine this concept with the resonant antenna. This novel antenna adopts two different resonant types operating two different frequencies. One is the conventional inverted-L monopole for higher operating band, and the other is λ/2 open-loop resonator for lower operating band. As these two different resonant types coupling each other, this antenna only need one feed network to produce dual-band purpose. This antenna is fabricated on PCB board and total size is 13×10mm2. In this thesis, we also establish the equivalent circuit model for this dual-band antenna to verify how important the coupling strength affects this antenna. From experiment, the resultant bandwidth is suitable for 802.11a/b/g WLAN applications. The radiation pattern is close to omni-directional, and the largest average gain can achieve around 0dBi for each measured frequency. Furthermore, we also verify the performance of this dual-band antenna is not affected seriously by the variation of FR4 manufacture parameter. Finally, we also utilize this novel dual-band antenna to design diversity antenna. In this diversity antenna, we use some simple barrier object occupying little size to decrease the coupling effect between two antennas.