本論文針對對稱式共面波導耦合線帶通濾波器的理論、設計流程及實驗，做了詳細的研究。 此對稱架構，可視為傳統型四分之一波長電容電感耦合型帶通濾波器與帶磚型濾波器的結合。為了設計成對稱式結構，我們使用了非對稱的三線式共面波導耦合線來設計，因而不需要額外的磅線或空氣橋來抑制奇模態的產生，故在實現時製作簡單是其中一個優點。此外，由於採用四分之一波長共振機制，不但有電路面積縮小的優點，更因為電路佈局的關係，其產生的寄生效應可在濾波器的通帶兩側各置入一個傳輸零點，藉此改善通帶附近的止帶衰減，以期符合系統規格需要。 在論文中，我們針對不同的佈局方式作比較，對於末端短路耦合線中心線接地實現的問題，也利用佈局的方式解決。 In this study, a class of symmetric CPW coupled-line bandpass filters is proposed. The proposed filters use the asymmetric three-line parallel-coupled CPW line and lump-element J- or K- inverters to realize symmetric CPW filter structures. Due to the symmetry, no bondwires or airbridges are required, which simplifies the fabrication process. The proposed filter structures are equivalent to quarter-wavelength resonator bandpass filters, such that they occupy only half the circuit area compared with the conventional ones, and the first spurious passbands of them occur at three times center frequency. In addition, by introducing the cross-coupling effect, two transmission zeros at the upper and lower stopbands can be created to further improve the selectivity. The working mechanisms of the proposed filters are described and design procedures are established in this thesis, so we can design the filter easily with the given specifications. Specifically, symmetrical CPW bandpass filters based on open-end and short-end parallel-coupled CPW line are designed and implemented, and the simulation results agree quite well with the measurement results.
