利用微帶線設計具寬止帶之微小化微波低通濾波器

Abstract

本文利用平行共振電路，藉由調整平行共振的衰減極點，設計在截止帶具有雙傳輸零點響應的平面微帶低通濾波器。此電路結構利用適當的平行共振，實現雙傳輸零點響應，以增加通帶邊緣的頻率選擇性。文中利用奇偶模態分析電路，由欲得之頻率響應估算出所需的傳輸線參數與容值，再利用電磁模擬軟體，微調整個電路的佈局。文中設計並製作可延伸截止帶至 6GHz 之 0.5GHz 頻寬的低通濾波器，並與實際量測結果比較。

A distributed parallel resonance circuit is used to design a very compact low-pass filter with cutoff frequency 0.5GHz. The circuit has a section of transmission line shunt with an interdigital capacitor connecting with two low-impedance lines at both of its terminals. A finite transmission zero can be generated near the passband edge so that the filter has a sharp transition response. In addition, the stopband can be extended to more than 6GHz by properly choosing the structural parameters of the circuit. The measured responses match with the simulation quite well.