橋式Ｔ型結構之低通濾波器設計

A Bridged-T Low Pass Filter Design

本文提出以兩條傳輸線，一條開路傳輸線與一電容組成一個橋式T 型結構之低通濾波器的設計。理論方面採用奇偶模對稱進行分析，得到電路的散射參數表示，因此本電路的傳輸與反射零點都可以準確的算出。並依分析結果運用於電路設計，分別設計3dB 截止頻率於400 與800MHz 之低通濾波器。電路的模擬以電磁模擬軟體（IE3D）完成驗證模擬，並以FR-4 板材及表面黏著電容器製作實際電路。模擬與量測結果具有良好的一致性。

In this paper, we propose a bridged-T low-pass filter design. The filteris composed of two transmission lines, one open stub, and a capacitor.Even and odd modes analysis methods are applied, for the filter is symmetricalbetween input and output ports. The results obtained from theoreticalanalysis are usable to find the transmission and reflection zeros and canhelp us in designing a low pass filter with prescribed specifications. Twoprototypes with 3dB cutoff frequency at 400MHz and 800MHz, respectively,are designed and fabricated on FR-4 substrate. The circuit layoutsimulation is performed by a full wave electromagnetic simulator-IE3D.The experimental results show good agreement with the simulated data.