孔徑效率改良之背接金屬共平面波導槽孔陣列天線

Abstract

在背接金屬共平面波導（CBCPW）中以主模（共平面波導模態）傳播電磁波，而此結構於任何頻率下皆會產生洩漏波向兩側傳遞。通常對於此架構下有兩種應用：一種是利用波往兩側洩漏的特性來作為天線的設計；另一種是利用特定方式來抑制此洩漏波，使它不要在兩側的方向上產生不必要的耦合及串擾。 利用全波分析去分析CBCPW結構，得知該洩漏波以某一角度偏離主軸傳遞，使波如同行進在平板金屬波導內。而在已知偏離角度下，我們沿該角度射線蝕刻矩形槽孔。利用矩形槽孔的特性，當槽孔長邊遠大於寬邊，並約等於二分之ㄧ波長（共振長度）時，電磁波便能有效地朝空氣輻射能量形成天線，最後可得一集中的邊射輻射場形。再利用槽孔天線等效電路之分析及全波模擬軟體去模擬整體天線陣列之傳輸及輻射特性，找出使天線的孔徑效率提升之方法，而設計出一高增益主波束垂直於陣列平面之高效率天線。 直播衛星收發天線運用在12GHz的頻段，要求高增益與高效率。本論文研究遂將天線的操作頻率設計在該頻段上，最後可得30.14dBi的輻射增益以及4.2GHz的頻寬。

Conductor-backed coplanar waveguide (CBCPW) propagates electromagnetic waves via dominant modes (coplanar waveguide mode), and excites leaky wave which propagates toward both sides despite the value of the frequency. In general, there are two applications based on this structure: first is to use such property to design the antenna; the other is to suppress the leaky wave through some methods in order to decrease the unnecessary couplings and crosstalk. Implementing the full wave analysis on the CBCPW structure, we can discover that the leaky wave propagates along a particular angle relative to the main CPW line, causing the wave to propagate as if in a parallel plate waveguide (PPW). Therefore, we can etch rectangular slots along the ground planes with the angle we have acquired. If the length of the slot is significantly longer than the width and approximately equals to half the guided wavelength, the slots fed by CBCPW will radiate power efficiently and we can thus obtain a centralized broadside radiation pattern. We then derive a method to improve the aperture efficiency of the antenna by analyzing the equivalent circuit of the slot antenna and also by applying Full Wave Spice, and eventually design a highly efficient antenna with a high main beam gain perpendicular to the array plane. The antenna for direct broadcast from satellites (DBS) is operated at 12 GHz and demands high gain and efficiency, which is also the frequency our antenna operates in, resulting in a radiation pattern with 30.14dBi and a bandwidth of 4.2GHz.