縮小化之寬頻耦合器

Abstract

本篇論文使用共平面波導的結構製作一個可以涵蓋2至6GHz的I/Q 混頻器。I/Q 混頻器是由三個基本元件所構成，包含一個寬頻耦合器、一個功分器和兩個單平衡式的混頻器。所以本論文先分別討論各元件的設計方法和製作，最後在組合成I/Q混頻器。 整個I/Q混頻器必須縮裝在小於一英寸見方的基板內，因此選用了三氧化二鋁基板(介電常數9.8)上有限地寬共平面波導來製作所有電路。 在這三個基本元件中，寬頻的90度耦合器為最困難的部份。其中耦合強度最強的中間耦合段，採用六線藍基耦合器來達成。能增進三節90度耦合器反射損耗的架構也會在此篇論文中討論。而在單平衡式混頻器製作上，採用了岔路環(rat race ring)當實現其中的180度分合波器。為了縮小面積和增加頻寬，我們使用反相器來取傳統岔路環的二分之波長180度移相器，且因為二極體是放在岔路環的中心，所以可以更縮小電路面積。

In this thesis, an I/Q mixer with operating frequency 2GHz to 6GHz is designed and fabricated. An I/Q mixer comprises three basic components, namely, a wideband coupler, a power divider and a single-balanced mixer. We will first discuss the design procedure of each component and then describe the implementation and integration of them to form a complete I/Q mixer. The whole I/Q mixer should be integrated into a substrate of a size less than 1 inch by 1 inch. The finite ground plane coplanar waveguide (FCPW) on the Al2O3 (with dielectric constant of 9.8) substrate is chosen to implement all circuit elements. The wideband three-section quadrature coupler is the most difficult part among three basic devices. In the tightest center coupling section, we propose a 6-line Lange coupler to achieve it. We also propose a method to improve the return loss performance of the quadrature coupler. The rat race ring 180 degree hybrid is used to implement the single-balanced mixer. In order to reduce circuit size and increase the bandwidth, a twist line phase inverter is used to replace the halve-wave 180 degree phase shifter of the conventional rat race ring. Besides, the diodes is placed inside the ring to further reduce the circuit size.