應用於極化分集之61-GHz雙饋入圓極化超大型微帶天線

Abstract

本論文提出一種以微帶線饋入之雙圓極化之超大型微帶天線，主要操作在61 GHz ISM頻帶。「超大型」之概念乃是有別於傳統操作在基頻的天線，由於操作在共振頻率較高的高階模態，天線的尺寸因此被等比例放大。因為毫米波頻段的特性，設計於61 GHz的傳統微帶天線大小與饋入傳輸線尺寸相當，造成阻抗匹配上的困難。本論文因而提出此大型微帶天線的設計，可有效解決此問題，不須要另外設計複雜的阻抗匹配電路。除此之外，由於天線尺寸相較於操作於基頻的天線較大，在61 GHz因製成技術的良率及製作誤差的容忍度可得到提升。 論文中的天線以截角方式實現圓極化，利用兩個正交微帶線饋入，使其擁有兩相互正交的極化方向，有效應用於極化分集。由於天線的面積較大，因此不須要使用天線陣列形式，其天線增益即可大於傳統微帶天線。此外，本論文採用深入饋入方式，增加兩個輸入埠之間隔離度之頻寬。所提出的天線為簡單的單層架構。 藉由實作在RO4003板材上，以設計於5.8 GHz ISM頻帶來進行實驗佐證，量測結果與模擬結果相近，天線饋入埠隔離度可達15 dB。在論文最後，未來會以此架構進行61 GHz之實作並量測。

In this thesis, a dual-feed dual circularly polarized oversize antenna is proposed for 61 GHz ISM band application. The term “oversize” means that comparing to conventional patch antenna operated at the fundamental mode, the proposed antenna is enlarged due to implemented at the higher-order mode. In millimeter-wave band, the dimension of the antenna is close to that of the microstrip feeding line which causes the feeding difficulties. This problem can be solved by the proposed antenna without any complicated matching networks. Moreover, since the dimension of the antenna is enlarged, the manufacturing tolerances can be increased. The proposed circularly polarized rectangular patch antenna with is achieved by truncating its two corners. By exploiting two vertically placed microstrip feeding lines, the proposed antenna has orthogonal circular polarizations for polarization diversity applications. Owing to its enlarged size, the oversize antenna has higher gain than that of the conventional one without using array design. In addition, this design is fed by two inset microstrip lines that can enhance the isolation between the two ports. The proposed design has a simple and single-layer structure. This design is fabricated on the RO4003 simulated and verified at the 5.8 GHz band. The simulated and measured results are in good agreement. Up to 15 dB isolation are achieved. The simulation of 61 GHz version is provided for future experimental verification.