以多模態及頻率轉換實現之多頻段濾波器及雙工器

Abstract

本篇論文主要提出兩種不同方法來改進多頻段濾波器及雙工器的設計。第一個部分是使用低溫共燒陶瓷技術之基板合成波導，研製三頻段濾波器，並延續此觀念設計兩個雙工器；第二部分則使用微帶線，研製兩個四頻帶濾波器。 第一個部份設計的概念是利用基板合成波導所形成的矩形共振腔中各模態之間場型具有正交性，因此兩共振器在不同模態下的耦合係數可藉選取適當的槽線位置去獨立控制。此外，若恰當地選擇饋入點的位置，亦能同時激發多個模態。如共振腔其中一個模態採用分裂型的雙頻響應，即可實現一具有改善頻段可調性之三頻段濾波器，且利用多模態正交性的結果，使用的共振器數目可減到最少。延續此概念，可進一步利用多模態的正交性設計雙工器，兩個模態能經由一適當的饋入點同時被激發，因此輸入端的共振器可共用，而不需額外的輸入匹配電路設計；在輸出端的設計，亦可找到兩個槽線能分別獨立萃取出兩模態的訊號，因此輸出端的共振器亦可共用且還能達到不錯的阻隔性。 第二部份則是針對多頻段濾波器，提出一通用的設計概念，其想法是將單頻段的濾波器藉由一轉換公式，將單頻的極點和零點根據各個頻段的截止頻率點去轉換配置成多頻段的極點和零點。此外，各個頻段可距離相當接近。最後提出兩個四頻段微帶線濾波器來驗證此設計概念。

This thesis aims at the improvement in multiband filters and diplexers by proposing two kinds of new design concepts. Based on the SIW (Substrate Integrate Waveguide)implemented on LTCC (Low Temperature Co-fired Ceramics), the first part designs a tri-band filter and elaborating the concept, two diplexers. The second part designs two microstrip quad-band filters. The LTCC SIW tri-band filter in the first part utilizes the concept of mode orthogonality in the rectangular cavity, thus the coupling coefficients between modes in two cavities can be controlled independently by the location of slots. Furthermore, multiple modes can be excited simultaneously with the proper feeding position. If one of the modes is applied by split-type dual-band response, a tri-band filter with improved band allocation can be realized with minimized number of resonators. Furthermore, two diplexers are designed by exploiting the multi-modal orthogonality. Two channel can share the same input resonator since two modes can be excited simultaneously; therefore the matching network is not needed in this structure. Also, two orthogonal slots opened in the common output resonator are designed to extract two modes independently and yet with good isolation. The second part proposes a general idea of frequency transformation for multiband filter design. The poles and zeroes of a single band response are transformed to poles and zeros of a multi-band response according to the cutoff frequency of each band. Two microstrip quad-band filters are presented to verify the concept.