利用輻射狀步階阻抗諧振腔設計超寬上截止頻帶之微帶線帶通濾波器

Abstract

本文提出新的輻射狀步階阻抗諧振腔，並使用其設計超寬上截止頻帶的微帶線帶通濾波器，已知步階阻抗諧振腔的諧振頻率會隨高低阻抗線段的阻抗和電氣長度比而改變，為了讓上截止頻帶變寬，第一高階諧波(f1)和基頻(f0)的比例必須盡量增大，要達到這個目標，需縮小低阻抗對高阻抗之比值，並找出最佳的電氣長度比；而本文提出的輻射狀步階阻抗諧振腔可以有效縮小低阻抗部分之特性阻抗。本文並利用輻射狀步階阻抗諧振腔的特點，合成並實作出數個帶通濾波器的電路，以實現超寬的上截止頻帶，其模擬與量測結果相當一致。

Microstrip bandpass filters with an ultra-wide upper rejection bandwidth are designed using stepped-impedance resonators (SIRs). The resonant frequencies of the SIR vary with impedance and length ratios of the low-impedance and high-impedance line sections. In order to widen the upper rejection bandwidth, the ratio between the first higher order harmonic and fundamental frequencies (f1/f0) should be maximized. Decreasing impedance ratio at a specific length ratio can reach this goal. The radial SIRs are proposed to effectively diminish the low-Z section□. Several bandpass filters composed of radial SIRs are synthesized and fabricated to realize an ultra-wide upper stopband. The measured results show a good agreement with the simulations.