本論文主要探討使用微帶耦合線實現以四分之一波長共振器為基礎的帶通濾波器原型電路，其電路面積較傳統使用二分之一波長設計者縮小達一半以上。透過適當的耦合線佈線方式，並引入二極體切換電路控制共振器電氣特性，我們設計出具有可切換通帶功能的濾波器，其在截止時，從直流到三倍中心頻處都能有20 dB的隔離度。藉由耦合線的傳輸零點特性，我們進一步設計出能抑制高階旁生通帶的帶通濾波器，30 dB止帶衰減的頻率上限可達四倍中心頻率。再者，利用耦合線帶通濾波器的反射係數相位特性，我們實現比傳統設計電路面積小的雙工器，並藉由引入交叉耦合改善雙工器的選擇度，以滿足現代通訊系統規格要求。 在本論文中，針對各式微帶耦合線的不同特性均詳細加以研究，並討論應用於濾波器與雙工器設計的最佳實施方式，而針對各種設計，均有一整套簡潔明僚的設計流程作為設計工具，同時也為未來進一步的改良提供更多的設計彈性。 In this study, several kinds of microstrip coupled-line structures are used to implement compact bandpass filters, which are based on quarter-wavelength resonators. Compared to the conventional parallel-coupled bandpass filters that are based on half-wavelength resonators, the circuit size of proposed filters are reduced by more than half. The passband of proposed coupled-line filter can be made switchable by a proper circuit layout along with the incorporation of diodes to change the resonance characteristics of quarter-wavelength resonators. An on-off isolation of more than 20dB up to 3 has been achieved. In addition, by utilizing the inherent transmission zeros of coupled-lines, the 30dB stopband bandwidth of proposed filter can be extended up to 4 . Moreover, by manipulating the phase of input reflection coefficient, we can implement diplexers based on proposed filter structures with smaller circuit size than conventional designs. Additional cross-coupling between non-adjacent coupled-line sections can also be introduced to improve the selectivity. In this work, the characteristics of different kinds of coupled-line sections are thoroughly investigated to make the best use of them in bandpass filter and diplexer designs. Simple and clear design flows have also been proposed for all designs, which allow the easy extension of proposed filter structures for further improvement in the future.
