因應現代無線通訊的發展，寬頻微波濾波器已日趨重要，傳統寬頻濾波器設計方法是利用增加結構中電磁耦合的方式實現，最大的瓶頸在於濾波器結構的耦合量因製程上的限制無法達到所需的要求。本論文提出一共平面波導結構的超寬頻(2GHz到8GHz)帶通濾波器，其比例頻寬超過120%。此帶通濾波器由高通及低通濾波器串接而成，通帶範圍的頻寬分別由高通及低通濾波器的截止頻率來決定，此種設計方法相較於傳統直接設計單一寬頻帶通濾波器的方法而言，不但設計的自由度提高，且能達到更寬頻的要求。此濾波器的兩截止頻率可輕易地經由分別調整高通及低通濾波器來實現，為一頻寬可調式的寬頻帶通濾波器。除此之外此濾波器在高頻及低頻止帶的特性均相當不錯，且在通帶邊緣的選擇度相當好。我們將此濾波器以FR4基板來實現，量測結果與模擬所得結果有相當好的一致性。對於此三種共平面波導濾波器，本論文亦提出其分別對應的等效集總元件電路，使得在設計上能更為簡便快速。 另外我們設計了一利用扇型短路截線的共平面波導至槽線寬頻轉接及寬頻指數型漸進開槽式天線，並將濾波器與此二元件整合成為一寬頻無線通訊系統前端天線模組，量測結果與模擬結果亦相當吻合。由於此天線模組的頻寬能經由濾波器控制，且為單一平面結構，故非常適用於單一平面微波單晶積體電路之寬頻收發系統。 Wideband bandpass filters are essential to modern broadband wireless communication systems. In the past, microstrip bandpass filter have been studied extensively. In contrast, there is little work on coplanar-waveguide (CPW) bandpass filters. The traditional design of wideband bandpass filter is realized via the enhancement of the electromagnetic coupling in structures. However, the limitation on fabrication processes renders the bandwidth somewhat limited. An ultra-broadband (2GHz-8GHz) CPW bandpass filter is proposed in this thesis. The CPW bandpass filter is designed via cascading CPW lowpass and highpass filters. The cascaded CPW bandpass filter is of greater than 120% 3-dB fractional bandwidth. Indeed, the cutoff frequencies of the passband are realized via separately adjusting the ones of the CPW lowpass and highpass filters. This approach offers more design freedoms than the traditional bandpass filter design. On the other hand, the proposed filter shows sharp skirt selectivity at both the passband edges and high stopband rejection. The proposed filter is fabricated for experimental verification. The measurement and simulation results are in good agreement. Also, the corresponding lumped equivalent circuits are demonstrated. Finally, the proposed filter is in conjunction with a broadband exponentially tapered slot antenna through a CPW to slotline transition for application demonstration.
