微帶線耦合器指向性改善之研究

Abstract

本論文是微帶線方向耦合器(Microstrip Coupled Line Directional Coupler)性能分析與改善，主要從二個方面來分析改善：第一是縮小面積，第二是改善指向性(Directivity)。縮小面積方面，一般弱偶合(例如30dB以上)的微帶線耦合器，二條耦合線間的間距要很寬(以35dB為例，在25mil，εr =10.2之基板上，其間距約為80~90mil)，若利用置入一條中央接地導線的方式，即可大幅縮小在弱耦合時的面積。改善指向性方面，將直線偶合器折成S型方式，即可降低Isolation，達到改善指向性的目的。最後將以上二個特性合併使用，做出即使在弱耦合情況下，仍然會有不錯指向性的微帶線耦合器。

This thesis attempts to analyze and improve the microstrip coupler's directivity. In the research，there are two major innovations. The first one is to reduce the area of a weak coupler，the second one is to improve its directivity. As of saving the area of weak coupler，if we use the traditional coupled line coupler，the distance between the two coupled line would be very wide (a 35dB on a substrate of 25mil，εr =10.2, the distance would be around 80~90mil). After we inserted a central ground strip，we found the area of the weak coupler could be reduced significantly. As of improving the directivity of the coupler，if we twist the straight line to the S-shape，we could reduce the isolation to improve its directivity. Finally，we could combine the two innovations together to have better performance. Even if in the situation of weakly coupled，we could still have better directivity.