具寬截止頻帶之極寬頻帶通濾波器設計

Abstract

本論文研究極寬頻帶通濾波器設計，並具有相當寬的截止帶。藉由微帶線至與平面波導之寬邊耦合，設計成輸出端與輸入端的饋入結構，並在其中間串聯一低通濾波器或帶止濾波器，以抑制因傳輸線的週期性特性的高頻諧波響應。本文先個別分析各組成電路特性，由輸出入端的微帶線至共平面波導寬邊耦合，進而利用雙埠網路分析串接的帶通和帶止濾波器的傳輸零點，同時考慮截止頻帶之抑制深度，並同考量3 dB頻率點，達到具寬截止頻的極寬頻帶通濾波器。本文實作三個電路以驗證設計理念，量測與模擬結果相當一致。

A new ultra-wideband bandpass filter structure with a wide upper stopband is proposed in this thesis. The microstrip-to-CPW with broadside coupling is designed to realize the input and output stages. To obtain a wide upper stopband, a lowpass or a bandstop filter is cascaded and placed in the middle of the input and output stages. By applying the proposed cascaded structure, the second resonant frequency of the broadside coupling structures can be suppressed. The microwave characteristics of the broadside coupled structure and the lowpass or bandstop stages will be analyzed individually. Then, the stopband rejection, 3-dB cut off frequencies and transmission zeros will be analyzed . As a result, ultra wideband passband filters with a passband from 3.1 GHz to 10.6 GHz and an upper stopband up to 20 GHz can be achieved. Three circuits are fabricated and measured to validate the design idea. Simulation and measurement responses show good agreement.