以四分之一波長步階阻抗共振器實現微帶線雙工器與雙頻濾波器之設計

Abstract

本論文主要提出了具有微小化與高隔離度特性的微帶線雙工器。它是由二個相鄰的四階交錯耦合帶通濾波器所組成，並且利用一個T型接面來將彼此相連。這些濾波器都是由四分之一波長步階式阻抗共振器所構成，除了能夠縮小面積外，還能使其擁有良好的止帶頻率響應。雖然這些濾波器兩兩相鄰很近，但是只要適當地設計T型接面，依然可以獲得良好的隔離度特性。而在所提出的雙工器中，也針對磁耦合共振器部分，探討其共用短路貫孔之可能性，並且提出了一改良設計。同時，吾人利用具有最短共振長度的四分之一波長步階式阻抗共振器來實現一尺寸最佳化之雙工器。然後，依據雙工器的設計方法，三種雙頻濾波器電路也分別被實現出來。最後，吾人亦嘗試整合前述之微帶線雙工器與平面天線，所以另外設計了二種以微帶線饋入之平面天線。 在本論文中所呈現的電路設計，包含雙工器，雙頻濾波器，微帶線饋入式天線與雙工器和微帶線饋入式天線的整合設計，也全都經由模擬與實驗量測來獲得証實。

A novel microstrip diplexer with a compact size and high isolation is proposed in this thesis. It is formed by two four-pole cross-coupled bandpass filters placed side by side and combined through a T-junction. The filters are designed with quarter-wave stepped-impedance resonators (SIRs) to achieve simultaneously size reduction and better control of spurious responses. Though the filters are closely placed, higher isolation can still be obtained by properly designing the T-junction. Moreover, the possibility for the magnetic-coupled SIRs in the proposed diplexer to use a common shorting via is also discussed, and a modified design is presented. An optimized design composed of quarter-wavelength SIRs with the minimum lengths is also demonstrated. Besides, based on the above design method, three types of dual-band microstrip bandpass filters are also proposed. Lastly, two microstrip-fed planar antenna designs are introduced and integrated with the proposed diplexer. The performances of all the circuits presented, including the diplexers, dual-band filters, microstrip-fed planar antennas, and the integrated diplexer and antenna, are all verified through both simulations and measurements, and they agree well.