在多層結構上以集總元件實現環形耦合器之設計

Abstract

隨著產品微小化的需求，通訊系統中的元件亦有小型化的趨勢，本篇論文針對180度分合波器中的環形耦合器作為主題，以集總元件本身低倍頻問題、且響應可預測的優點來取代傳輸線，再搭配多層結構電路板可垂直整合縮小面積的特性，來達成小型化的環形耦合器設計。文中共做了兩種類型的環形耦合器設計，第一種是單通帶的環形耦合器設計，第二種是雙通帶的環形耦合器設計。兩者皆以目前ISM頻段的2.4 GHz 為主要中心頻率來做設計。 第一種單通帶的環形耦合器設計，是採用高通及低通的集總模型來取代傳統傳輸線，在此我們先採用了一個兩層的印刷電路板來製作簡化後的窄頻結構，藉以驗證集總元件模組模擬與量測的差異及實際響應，其中在面積的縮減及倍頻的抑制皆達到不錯的效果。其後再針對結構增加集總模型的階數，設計一寬頻的架構，再採用多層設計的低溫共燒陶瓷製程來設計此結構，達到對比於傳統環形耦合器縮減至1.37%的面積，以及50%的工作頻寬結果。 第二種雙通帶的環形耦合器，採用本論文提出的一種新的雙通帶傳輸線架構，以架構本身在共振點前後反相的特性，使環形耦合器在兩個不同頻率的通帶產生一組具有對偶關係的響應，達成雙通帶的環形耦合器設計。在此同樣以一階的架構在兩層板上做出一窄頻結構的設計，為驗證可將第二個頻帶做於二倍頻之內，故將第二個頻率點設計於4 GHz。此外，為配合各種系統的需求，最後亦增加階數來驗證強化頻寬結構的可行性，方便日後之設計。

With the demand of miniaturized products, size reduction of elements has become a trend in communication systems. This thesis takes rat-race coupler which is part of 180° hybrid coupler as the main research topic. Combining the advantage of lumped elements – low spurious problem and predictable response – with multilayer PCB process, circuit layouts can be integrated vertically to realize a miniaturized rat-race coupler. Two types of rat-race coupler design are proposed in this thesis – a single passband design and a dual passband design. Both of them are designed at 2.4 GHz, which belongs to ISM band, as the main center frequency. The single passband rat-race couplers design uses which use high-pass and low-pass lumped model to replace the transmission lines. At first, a simplified narrow band structure is realized on a 2-layer print circuit board. Responses of ideal and actual lumped elements are verified with simulation and measurement, good results on area reduction and spurious suppression can be observed. A broader bandwidth structure is then achieved by increasing the order of the 270° transmission line section. This structure is designed and fabricated with low temperature co-fired ceramics (LTCC) process. A 1.37% area compared to conventional rat-race coupler and a 50% fractional bandwidth were obtained. The dual passband rat-race couplers design adopts a new kind of dual passband lumped circuits. A pair of dual rat-race coupler responses can be constructed by utilizing the phase reversion characteristics before and after resonance, thereby achieving the dual passband feature. A narrow band structure is designed with 1st order lumped circuit model on a 2-layer print circuit board, which takes 4 GHz as the second passband center frequency to verify the feasibility of a second passband below its spurious passband. Finally, an enhanced bandwidth structure designed by increasing the order of lumped circuit model is also simulated, which could be applied to other systems.