於平行耦合濾波器中使用L型諧振腔植入傳輸零點之設計與合成

Abstract

傳統的平行耦合微帶線帶通濾波器在通帶附近沒有零點，本文提出利用耦合方式加入L型結構來產生零點。一個三線平行耦合微帶線加上開路殘段可視為單級，根據此等效電路，可進行具有極平坦響通帶應的平行耦合帶通濾波器之合成。除了零點如預期產生之外，也可實現類似橢圓函數響應將選擇性提高。最後，實際製作電路並量測來驗證。

There is no transmission zero in the response of a traditional microstrip coupled-line bandpass filter. In this thesis, transmission zeros are created by inserting an L-shape resonator to the input and output coupled stages. The stages consist of a three-line structure and one of the line is loaded by an open stub. The equivalent circuit of the three-line stage is derived. Based on this equivalent circuit, we can synthesize a parallel coupled-line bandpass filter with a maximally flat response and transmission zeros near the passband. Several circuits are fabricated and measured to compare with simulation results. They have good agreement.