平面及共平面傳輸線之漏波現象和多模效應

Abstract

平面及共平面傳輸線在開放之結構下會引起外漏而導致相鄰元件的交互耦 合及功率損耗。在這種外漏波導中，實際結構大小對漏波行為的影響仍須 深入研究並建立其模型。以網路表示並考慮金屬模之全波模匹配法在此用 於研究一個加蓋的且俱有有限金屬帶電導及厚度的微帶之漏波特性。理論 結果和已發表及厚度的微帶之漏波特性。理論結果和發表之主要模及波特 性極為吻合。有限金屬帶電導及厚度在第一奇對稱漏波取影響已被嚴謹研 究及報告。一個厚的且積體化於無限或有限寬基板的微帶之漏波傳播特性 也發表於此。場論的結果表現出了金屬帶的有限厚度能轉化一個束縛模至 一個漏波。另一方面，當無限基板寬減少至一個有限值，主要模的漏波特 性變成了一束縛模，且發現了其他漏波的存在。這些有限金屬帶厚度及基 板寬度對漏波的影響將在此討論之。甚之，一個有限寬度之印刷傳輸線結 構可能存在多模傳播的特性。這種效應將使整個基體電路優越度變壞。本 論文發表了一有限寬度金屬背撐式共平面波導(FW-CBCPW)的理論及實驗結 果。FW-CBCPW的導波特性第一次在此利用嚴謹的模匹配法加以研究。當考 慮一段FW-CBCPW傳輸線被放置在一個實驗室常用的測試座上，藉由將FW- CBCPW視為一簡單的耦合傳輸線在傳輸特性上所觀察到的不正常行為，牽 系統，散射參數可由理論上得知。實驗結果也和理論值非常吻合。特別是 涉到被測試座短路兩端的側板的共振現象。有限背板寬之共平面波導散射 參數的實驗結果也發表於此篇論文中。若同樣視此有限背板寬之共平面波 導為一耦合傳輸線系統，此模型所得之理論結果依然和實驗值吻合。有限 背板寬的效應經由顯著的共振頻率偏移而得到驗証。最後，一項模抑制技 術將介紹於此。利用側牆連接FW -CBCPW側板至地板能抑制不必要的擬微 帶模，且提供了一個很寬的單模傳播頻率範圍。如果二側牆的間隔距離被 適當的設計，則高次模的漏波及共振現象將可避免。 The open nature of the planar and coplanar transmission line can cause leakage that results in cross-talk between neighboring elements and loss of power. In such leaky waveguides, the effects of practical structural dimensions on the leakage behavior still remains to be explored and modeled. A network representation of full-wave mode-matching method employing the metal modes is applied to the investigation of the leaky wave. The effects of metal thickness, conductivity and finite substrate width on leaky waves are discussed. Furthermore, a printed transmission line of finite-width configuration may exist the characteristic of multimode propagation. Such effect degenerates the performance of the integrated circuits. This thesis presents theoretical and experimental results for a finite-width conductor-backed copla -nar waveguide (FW-CBCPW). The guiding characteristics of FW- CBCPW are investigated first by the rigorous method of mode matching. A FW-CBCPW through line is then placed within a test fixture commonly used in laboratories, and the scattering para- meters of the through line are obtained theoretically by appro- ximating the FW-CBCPW as a simple system of coupled transmission lines. Experimental results are shown to agree very well with the theoretical ones. Finally, a technique of mode suppre- ssion isintroduced in this thesis. The connection of the side planes of the FW-CBCPW to the ground through lateral walls suppresses the undesired microstrip-like (MSL) mode and provides a wide frequency range over which the single- mode propagation occurs. The leakage or resonant phenomena of the higher-order modes can be avoided, if the distance separating the lateral walls is carefully designed.