利用L形槽線之組態可變天線設計

Abstract

此論文著重於利用L形槽線之組態可變的天線設計。首先提出一具可切換輻射場形的陣列天線，該陣列由四根L型的四分之一波長槽線天線所組成，並透過二極體控制每根天線動作與否。由於該槽型天線元件在槽線開口處具有較強的輻射，因此將四根天線的槽線開口分別朝向四個方向。當不同天線動作時，天線陣列的輻射場形可切換至特定的方向上。論文中實作一適用於無線區域網路之2.4-2.5 GHz天線來驗證設計的構想，該天線具有八種方向性和多個近似全向性的輻射場形，而其面積僅 。論文中亦詳細討論天線的相關係數、輻射特性等。相較於傳統的可切換輻射場形陣列天線，我們提出的天線具有精巧且低製作成本的特性，未來可應用至數位家電相關產品，以提升無線資料傳送的傳輸率和可靠性。 接下來提出一個可應用來設計場型、頻率或場型/頻率可調整的天線架構。該天線結構主要由L型槽線、二極體、電容器和偏壓電路組成。透過控制二極體動作與否來改變槽線周圍的感應電流分布，進而形成ㄧ輻射場型可調的天線。簡單地修改天線的參數，該架構可用來設計頻率可調整的天線。更進ㄧ步，若將電容器以可變電容器取代，並增加一些控制線路，該架構可以用來設計場型/頻率皆可調的新型天線。我們利用此架構實作多具天線來驗證設計的構想。提出的天線結構具有低製造成本、平面架構等特點，未來可應用於小型的手持設備如智慧型手機或筆記型電腦等產品。

This dissertation focuses on the design of compact reconfigurable antennas using L-shaped slots. A compact switched-beam antenna is proposed firstly. The antenna is composed of a four-element antenna array based on L-shaped quarter-wavelength slot antenna elements. Such an antenna element is a planar structure and presents a directional radiation pattern on the azimuthal plane. Its maximum radiation direction is toward near the direction of the open end of the slot. As a result, the open ends of the four slot antennas are arranged toward 0, pi/2 , pi, and pi*3/2, respectively. The statuses of these antennas are controlled by some diodes. Consequently, by carefully controlling the diodes, an antenna with several switchable patterns can be achieved. To prove the concept, a 2.4-2.5 GHz switched-beam antenna for WLAN applications is designed and implemented. Its size is 52mm in square. The antenna possesses eight directional patterns and many nearly omni-directional patterns on the azimuthal plane. The envelope correlations and the characteristics of the designed antenna are also discussed in the dissertation. Due to the compact size and low manufacture cost, such a design can be a promising solution for digital home applications to overcome multipath problems and increase the transmission data rate. Next, a basic antenna structure to design pattern, frequency, and pattern/frequency reconfigurable antennas is proposed. The structure consists of an L-shaped slot, PIN diodes, lumped capacitors, and bias networks. The PIN diodes and the lumped capacitors located at specific positions are used to create short circuits across the slot. By carefully controlling these diodes, the induced current distribution around the slot can be changed, resulting in different antenna radiation patterns. Thus, a pattern reconfigurable antenna can be achieved. The proposed structure is then extended to design frequency and frequency/pattern reconfigurable antennas by simple modifications. A series of compact reconfigurable antennas based on the proposed structure is designed and implemented to prove the design concepts. Owing to the compact size, low manufacture cost and planar feature, the proposed structure can be applied to compact wireless devices such as smart phones and notebook computers.