本論文提出一個新式帶通濾波器架構，並使用共平面波導傳輸線來實現，其結構的組成為於阻抗及納導轉換子之間加入傳輸線共振器交錯串接。其中傳輸線共振器結構由一段傳輸線串聯一短路傳輸線所組成，而短路傳輸線可置於共面波導訊號線裡，使傳輸線共振器長度縮小。相較於傳統以四分之一波長傳輸線共振器設計的帶通濾波器，共振器長度可縮小約一半，而與傳統步階式阻抗共振器相比，則可藉由共振器本身的傳輸零點來抑制旁生通帶將止帶上限往高頻提升。針對此新式濾波器，提出對應的等效電路與設計公式，以便利於設計。論文中以共面波導實作四階的帶通濾波器，中心頻率為2GHz，植入損耗在1.66~2.34GHz小於2dB（比例頻寬34%），30dB止帶頻率上限可達四倍中心頻率，全波模擬與量測結果亦有相當好的吻合度。 In this study, a novel bandpass filter structure is proposed and realized using the coplanar waveguide (CPW) structure. The filter is based on the alternate connection of proposed resonator, impedance inverter, and admittance inverter. The proposed resonator consists of a transmission line and a short-end series stub. The short-end series stub can be patterned inside the center conductor of CPW and thus reduces size of resonator. As a result, the length of the proposed transmission-line can be reduced to less than half that of the conventional uniform quarter-wave transmission line resonator. Spurious responses are suppressed using the inherent transmission zero and thus increase the stopband bandwidth. This is an advantage of proposed filter over the conventional stepped-impedance filter. Specifically, fourth-order CPW bandpass filters are designed at 2GHz and the insertion loss is less than 2 dB between 1.66 and 2.34 GHz. Spurious suppression is better than 30dB up to four times the center frequency. The measurement results agree well with the simulation results.
