以微帶線環型共振腔設計具有微小化寬截止頻帶帶通濾波器

Abstract

本論文提出兩種微小型帶通濾波器的設計。第一種濾波器的設計是在方環型諧振腔的四邊中心加上電容性負載的箭頭型殘段，這些電容性負載所造成的慢波效應，使得諧振腔的基頻(f0)可以降到比傳統均勻阻抗環型諧振腔的基頻還低的頻率點，達到縮小諧振腔總面積為傳統環型電路的50%以下的目的。第二種結構則是引入步階阻抗的結構在環型諧振腔中，形成週期性步階阻抗環型諧振腔。利用週期性步階阻抗諧振腔的共振特性，並適當的安排諧振腔的結構參數，可降低諧振腔基頻，進而縮小諧振腔面積為傳統環型電路的40% 以下。同時，步階阻抗環型諧振腔亦具有將諧波（虛假響應）頻率拉高的特性，因此得以加寬上截止頻帶，達到3.7倍中心頻以上。本論文亦實作數個電路，以資驗證。量測結果顯示與模擬結果相當一致。

An optimal ring resonator and a new square loop resonator are proposed for designing miniaturized dual-mode bandpass filters. In the first resonator, the center of each side of the loop resonator is tapped with a capacitive arrow-shape open stub. The whole resonator encloses four coupled compact miniaturized hairpin resonators. The slow-wave effect caused by the capacitively load can reduce the fundamental frequency of the loop resonator. As a result, this miniaturized loop resonator can be used to synthesis a miniaturized dual-mode bandpass filter. In the second resonator, the fundamental frequencies and higher order resonant harmonics of ring resonators with different numbers of impedance steps are analyzed against the length and impedance ratios of the hi-Z and low-Z segments. It is found that the optimal numbers of impedance steps and length can be obtained for a given hi-Z to low-Z impedance ratio to minimize the filter size and maximize the upper rejection bandwidth. Both the proposed bandpass filters not only have good spurious-free performances, but also achieve more than 50% size reductions, as compared with a conventional dual-mode ring bandpass filter. The measured results show a good match with the simulated responses.