本論文提出以短截線結構設計一超大頻寬帶通濾波器並實現在共平面波導結構，其比例頻寬為116%，結構尺寸非常小，對諧波通帶有非常好的抑制能力，且在通帶邊緣的選擇度亦相當好。此設計為串接一帶通濾波器及一帶拒濾波器，其帶通濾波器實現方式為結合四分之一波長並聯短路截線結構及四分之一波長串聯開路截線結構；帶拒濾波器為結合四分之一波長串聯短路截線結構。此濾波器之通帶寬度可分別介藉由控制並聯短路截線結構及串聯開路截線結構之長度，其截止通帶之寬度可藉由串聯短路截線結構達到改善。本論文所提出之超寬頻濾波器設計相當簡單、直接，量測結果與模擬結果亦相當吻合，我們亦從電路的觀點提出其對應之等效電路。 This thesis describes the design and characterization of an ultra-broadband bandpass filter (BPF) realized solely with coplanar waveguide (CPW) stub structures. The demonstrated CPW- BPF has a fractional bandwidth (FBW) of 116%, very compact in size (about a half-wavelength), great stopband rejection, and sharp selectivity. Technically, the BPF is essentially realized with a quarter-wavelength series open stub and a quarter-wavelength shunted short stub. The higher and lower cutoff frequencies are mainly related to the electrical length of the shunted short stub and the series–wound open stub, respectively. The stopband rejection (blocks undesired signals and suppresses spurious harmonics) is enhanced through an incorporation of CPW bandstop structures. It is shown that the proposed design methodology is a straightforward and relatively easy means for the realization of broadband bandpass filters. The proposed filter design is verified through experimental demonstration. The corresponding lumped equivalent and transmission-line equivalent circuits are provided for circuit design purpose.
