二維無限波長多埠分波器與PIN 二極體控制切換波束天線之設計

Abstract

在無線通訊系統中，使用傳統全向性天線，訊號的傳輸易受到多重路徑衰減 (multi-path fading)和同類信號干擾的影響而遭受破壞，為此，我們常希望能透過改 變天線波束方向與形狀來達到減少同頻干擾的效應，以及因多重路徑傳輸所造成的信號 衰弱現象，以增加訊號增益，提高通訊品質。在本論文中，我們將提出一個採用平面印 刷電路板技術所實現的2.45GHz 切換波束式天線。本篇論文的第一個主題是先設計一個 二維多埠分波器。由於後設材料(metamaterials)具有很多獨特的性質，我們利用蕈狀 結構來設計一個二維複合左右手傳輸線(composite right/left handed transmission line)，並利用後設材料的無限波長特性來設計出二維無限波長多埠分波器，並運用在 後面的切換波束天線上。在第二個主題中，我們將提出一個新型的切換波束天線，結合 了我們所設計的二維多埠分波器、PIN 二極體控制電路，與具單波束指向性的彎折式半 波長偶極天線。透過利用PIN 二極體的導通與否，來激發一支天線、或同時激發兩支天 線做波束合成，使得主波束有45 度的旋轉可能，於整個平面共可提供八種方位以配合 實際應用需求。設計出來的天線具有尺寸適中、容易設計以及不錯的天線輻射特性。

In wireless communications, using traditional omni□directional antennas will be subjected to the effect of multi□path fading and co□channel interference. Thus, we often hope to change the direction and the shape of the antenna beams to increase the signal gain and improve communication quality. In this thesis, we present a PIN□diode□controlled beam□switching antenna operating at 2.45GHz which can be realized by planar printed circuit board. A two□dimensional N□port power divider is proposed in the first topic. Since metamaterials exhibit many specific electromagnetic properties, we use 2□D mushroom structure to create 2□D composite right/left□handed transmission line, and design our 2□D N□port power divider using infinite wavelength phenomena. In the second topic, we combine the 2□D N□port power divider, PIN□diode□controlled circuit, and meander line half wave dipole with single beam to realize a novel beam□switching antenna. By controlling the PIN□diodes, the proposed antenna provides eight directivities, and each directive pattern can be rotated by 45 degrees with different switching states. The antenna we present in this thesis is easy to design. It also has medium dimension and good radiation performance.