以耦合矩陣合成帶通耦合器

Abstract

本論文研究以耦合矩陣合成帶通耦合器，為實現該矩陣，本文亦介紹不同的耦合類型以及如何萃取耦合係數與外部品質因子。首先回顧帶通耦合器的概念架構與原理，已知其頻率響應可藉由耦合矩陣合成。 在實作部分之一，以二分之波長步階阻抗諧振腔設計兩個180度帶通耦合器，其輸出埠可藉由加入源載耦合(source-load coupling)產生零點，並以耦合矩陣推導出其解析解。 實作部分之二為90度帶通耦合器，本文使用四分之波長步階阻抗諧振腔合成，設計時藉由選擇適當的阻抗比和電氣長度比，可達成尺寸最小化與最佳的截止頻帶，使用面積僅為傳統90度耦合器的31.4%，截止帶在頻率3.6 f0前的衰減量皆在30dB以上。本文亦用四分之波長諧振腔實現一個較寬頻與改善頻率選擇度的雙級90度帶通耦合器。 本文將實作電路的量測結果與電路模擬軟體運算數據比較，一致性相當好。

This thesis investigates coupling matrix synthesis of filtering couplers, i.e. couplers with a bandpass response. First, the structures and the design theory of filtering coupler will be introduced. It is known that such multiport devices can be synthesized by coupling matrix approach. To implement the matrix elements in a real circuit, the extracting of coupling coefficient between resonators and external quality factor of a singly loaded resonator will be reviewed. In realization, two 180°-bandpass couplers are synthesized by stepped-impedance resonators. Transmission zeros are created by employing source-load coupling. The analytical solution of the zeros is also derived. In addition, a 90° filtering coupler is also designed with 90° stepped-impedance resonators. By choosing proper impedance and length ratios, the size of the resonators can be minimized and the first spurious can be pushed far away from the passband. As a result, it occupies an area only 31.4% that of a traditional branch-line coupler, and the attenuation level is 30 dB or higher before the first spurious at 3.6 times the passband frequency. A two-stage 90° bandpass coupler is realized with 90° resonators, to have a wider bandwidth and improved passband selectivity. The measured results of all fabricated circuits show good agreement with the simulation responses.