小型柴比雪夫耦合線低通濾波器分析與設計

Analysis and Design of Reduced-Size Chebyshev Coupled-Line Low Pass Filters

本文提出以兩對耦合線及兩條開路傳輸線組合之小型柴比雪夫低通濾波器設計。此濾波器具有接近截止頻率陡直響應特性、結構簡單、截止頻寬較寬、體積小等優點。濾波器的特性分析以傳輸線段及耦合傳輸線等效模型電路進行，經推導後得到T型等效電路，可依此由低通原型濾波器逐步設計出低通濾波器電路。為驗證電路設計流程之正確性以兩種不同截止頻率分別為2.45與5.2GHz進行設計。結果顯示實際測量與模擬結果有相當高的一致性。

A low pass filter consisting of two coupled-lines with open-stubs is proposed. This filter has a sharp skirt response, wide rejection bandwidth, and is simple and small. The low pass filter was analyzed by coupled-line and transmission line models and resulted in a T type lumped element equivalent circuit. By applying this T type equivalent circuit and incorporating a Chebyshev low pass prototype table, a design procedure was established. Two prototype circuits with 3dB cutoff frequency at 2.45 and 5.2GHz were designed, respectively, utilizing this design procedure. The measured and simulated results show good agreement within the frequency range 0~10GHz.