三種具可調頻寬之雙模雙頻帶通濾波器

Abstract

本論文提出三種可調頻寬之雙模雙頻帶通濾波器。第一種利用步階阻抗諧振腔實現雙頻帶濾波器，並在諧振器中間接上一段短的接地高阻抗傳輸線，以提供電感性耦合。為增加設計自由度，一指叉式電容設計於諧振器的中央，即可控制兩通帶的頻寬與中心頻率。此外，進一步利用源端與負載端的耦合，以形成多個傳輸零點，增進兩通帶的頻率選擇度。此部份實作兩雙頻帶通濾波器，量測與模擬結果吻合。

本文第二種雙模雙頻帶通濾波器，利用雙端接地之步階阻抗諧振器，以兩段短的高阻抗線頭尾相接，以形成雙模雙頻帶通濾波器。藉由調整電感性耦合的大小，可控制兩頻段頻寬。除此之外，利用斜對稱饋入，以產生兩個傳輸零點，進而改善兩通帶的頻率選擇度。第三種雙模雙頻帶通濾波器使用與第二種帶通濾波器相同的諧振腔，但將其兩接地孔相互連結以形成單一的接地孔，可降低製作上的誤差，電路佈局可更為緊密並節省電路面積。本電路亦可利用源端與負載端的耦合，產生多重傳輸零點，大幅提高兩通帶的頻率選擇度。此兩部分亦各實作兩個電路，以驗證設計理論，量測與模擬結果相當一致。

Three dual-mode dual-band bandpass filters are proposed in this thesis. The first dual-mode dual-band bandpass filter is devised based on a single stepped-impedance resonator. The center of the resonator is grounded through a short high-impedance section, which is equivalent to an inductor for providing coupling between the resonant modes. In addition, in order to increase the degree of freedom for dual-band design, an interdigital capacitor is introduced so that both center frequencies and bandwidths of two passband can be controlled. Moreover, with the aid of source-load coupling, two extra transmission zeros can be created close to the passband edges and hence greatly improve the frequency selectivity between the two passbands. Two filters are fabricated and measured to validate the proposed idea. The measured results show good agreement with the simulation.

The second dual-mode dual-band bandpass filter is again designed based on two stepped-impedance resonators. Both ends of each resonator are terminated to the ground. For the dual-mode operation, the two stepped-impedance resonators are connected to the ground via by two short high-impedance sections. The inductive coupling is provided to control the bandwidths of the two passbands. With a skew symmetric feed structure, two transmission zeros are created between the two passbands. To obtain a simpler fabricated process and more compact circuit area, the third dual-mode dual-band bandpass filter is evolved from the second filter with two ground vias being connected to a single one. With the aid of source-load coupling, again, transmission zeros are generated to improved the selectivity of the two passbands. Two microstrip circuits are fabricated and measured to validate design ideas of the second and third bandpass filters. The simulation and measurement results show good agreement.