新式的多模諧振腔濾波器

Abstract

本篇論文提出ㄧ種新式的多模態諧振腔濾波器，其主要的特點是具有一個可調整的傳輸零點和大範圍的上止帶，設計方法是將濾波器的諧振頻率調到與Chebyshev 通帶的傳輸極點相同位置，當我們將耦合量增強，便可產生一個形似Chebyshev 的頻率響應，可調的傳輸零點由傳輸零點頻率的四分之一波長開路支線傳輸線產生，且此開路支線傳輸線並聯一個電抗，即決定傳輸零點出現在下止帶或上止帶，本篇中有三個2.45GHz 三模態諧振腔濾波器的設計，量測結果皆與模擬相符合。 本篇有另一個濾波器設計方法是使用中間為並聯電抗或串連電納，兩邊為阻抗不相等傳輸線，所形成的K 倒反器或J 倒反器來合成濾波器，傳統的方法是使兩邊的傳輸線阻抗相等，因此，我們的設計更為靈活。我們將重點放在K倒反器上，J 倒反器可同理推得，跟上ㄧ個主題相仿，此處也有ㄧ個由傳輸零點頻率的λ/4 開路支線傳輸線所產生的可調傳輸零點，此傳輸線可視為並聯電抗，在兩端加上兩段不同度數、不同阻抗的傳輸線，等效成一個K 倒反器，本篇中實作兩個2.45GHz 的三階濾波器以驗證理論。

Novel planar bandpass filters with a configurable finite transmission zero and wide upper stop-band are synthesized based on multimode resonator property. The resonances of the resonators are tuned to match the transmission poles of a Chebyshev pass-band in order to create Chebyshev-like response while enhancing the coupling. The transmission zero at finite frequency is brought about by a open-circuit stub with quarter-wavelength of zero frequency. Additionally, the open-circuit stub connecting a shunt reactance can be used to allocate that the transmission zero in the lower or the upper stopband. Tri-mode bandpass filters with the transmission zero on the different sides of the passband are designed. The measured results both show good agreement with simulated responses. Another design included in this article is the filter with K or J inverter making use of unequal impedance microstip lines with shunt reactance or series susceptance in between. It’s more flexible and much different from the conventional design having equal impedance microstrip lines on the both sides. We discuss the K inverter design only since the design guidelines are the same as those of the J inverter. A centered open-circuit stub is taken to be the reactance and utilized to tune transmission zero position. Third-order band-pass filters with transmission zeros on the different sides of the passband are designed and measured to validate the approach.