以接地細帶降低低阻抗微帶線阻抗的方式來設計小型化微帶線四分之一波長步階阻抗濾波器

Abstract

本論文提出一種新方式來將傳統的步階阻抗微帶線諧振腔縮小化。在此諧振腔結構中低阻抗部份的微帶線插入接地細帶，可以提高微帶線的等效電容，使得其特性阻抗值更為降低；與傳統的微帶線架構相比較，使用文章中所提出的方式，可以將微帶線的特性阻抗值轉換成有很大一部份由在同一平面上的訊號線及接地細帶所控制；論文中對於在諧振腔中插入接地細帶的觀念及特性有詳細地討論，同時也探討了將此種結構實際應用於平面濾波器電路上，接著也引入了交錯耦合的觀念，使濾波器在通帶二側產生一對傳輸零點來增加其選擇率，模擬及實際量測結果在文章中均有所提出。

A new method to miniaturize microstrip step impedance resonator structure is proposed in this theses. Inserting ground strips in the low impedance microstrip segment results in a high effective capacitance that makes the characteristic impedance lower. Therefore, the characteristic impedance of the microstrip line is mainly controlled by the signal strips and the inserted ground strips in coplanar manner. The concepts and characteristics of this modified resonator structure are described in detail. Practical applications for planar bandpass filters employing the features of this resonator structure are discussed and fabricated. Besides, additional cross coupling structure which produces a pair of transmission zeros near the passband is also introduced to improve the skirt characteristics. Both simulated and measured results are presented.