縮小化多頻微波枝幹耦合器之設計

Abstract

本篇論文研究的重點在於使用集總元件實現、改進多頻帶的微小化枝幹耦合器。第一部份是使用集總元件所構成的雙通帶傳輸線架構取代傳統耦合器中的90度傳輸線，以設計雙頻帶枝幹耦合器；第二部份則是使用傳統傳輸線以及集總元件構成的共振器，設計三頻枝幹耦合器。 第一部份的設計概念是利用一個雙通帶傳輸線模型，以架構本身在共振點前後相位相反的特性，使此傳輸線架構在共振點前後分別等效為低通以及高通的集總模型，因此可形成兩個通帶使枝幹耦合器具有雙頻帶的特性，並藉由整合被動元件製程來製作此電路以同時達到多頻段及微小化的目的並與理論相互驗證。 第二部份則是利用將LC並聯共振器與開路傳輸線的串聯電路接在一傳輸線的兩端，使它在指定的三個頻率均補償為90度的傳輸線。以此想法，先使用傳統傳輸線做為耦合器的中心結構，再加上四條開路傳輸線可實現三頻段的枝幹耦合器，因傳統傳輸線電氣長度與阻抗的限制，這個設計的耦合器只能實現在三個等頻距的頻段，因此使用步階式阻抗傳輸線取代原傳輸線，利用其阻抗與電氣長度之間較彈性的關係，以及開路殘段所提供的慢波效應與LC並聯共振器的共振，實現在任意三個頻段的枝幹耦合器。此外，由於步階阻抗傳輸線的使用，電路面積也較使用傳統傳輸線的設計小。

The thesis aims at the realization and improvement of compact multi-band branch-line couplers using lumped elements. The first part designs a dual-band branch-line coupler by substituting the λ/4 transmission lines in the conventional coupler with dual-band lumped circuits. The second part designs a tri-band branch-line coupler with conventional transmission lines and LC resonators. In the first part, the conventional transmission lines are substituted by the dual-band transmission models with the phase reversion characteristics before and after resonance which are equivalent to the low-pass and high-pass lumped models, respectively. With compact lumped elements realized in integrated passive device (IPD) technology, the coupler achieves dual-band characteristic and size reduction at the same time. The second part, the series circuits composed by LC shunt resonators and open stubs are shunted at each end of the transmission lines to adjust for 90º phase. Based on this concept, the coupler is realized by using the conventional transmission lines for the branches and the shunted series circuits. Because of the limit of the electric length and impedance of the transmission line, the tri bands of the coupler will be equally spaced. For three arbitrary frequencies, the stepped-impedance transmission line is introduced. With the flexible phase and impedance responses of the stepped-impedance section and the slow-wave effect contributed by the open stubs and the resonance of the LC shunt resonators, the tri-band branch-line coupler with arbitrary operating frequencies is realized. Besides, because of using the stepped-impedance section, the circuit area of this design is smaller than the one using the uniform-impedance one.