本論文之三工濾波器之通帶是由短路半波長共振器所組成的，帶通濾 波器的通帶是由 4 個共振器所控制的，並使用開路殘段在其他通帶頻率點 創造一個傳輸零點，來增加電路間的隔離度，最後在使用 T 型饋入線來直 接饋入輸入能量。 第一個電路是由短路半波長共振器加上開路殘段所組成的雙工四階濾 波器，中心頻率分別是 1.8GHz 及 2.1GHz，並在 1.8GHz 的濾波器上在 2.1GHz 的頻率點上設計一個傳輸零點，最後再使用直接饋入的方式做輸 入，這樣可以使兩個濾波器的隔離度大於 50dB。 第二個電路是在原有的電路基礎上再設計一個中心頻率為 1.5GHz 的 濾波器，並在 1.8GHz 的頻率點上設計一個傳輸零點，最後再與其他的濾 波器組合成一個三工的濾波器，其隔離度也都大於 50dB，但本論文採用 T 型直接饋入的方式做輸入，因此設計與調整各個濾波器的輸入阻抗將變得 尤為重要。;This thesis focuses on the design of a triplexer composed of short-circuited half-wavelength resonators for the passband. The passband of the bandpass filter is controlled by four resonators. Open-ended stubs are used at other frequencies within the passband to create a transmission zero, enhancing the isolation between different circuits. The triplexer utilizes a T-shaped feeding line for direct input energy feeding. The first circuit is a dual-band fourth-order filter consisting of short circuited half-wavelength resonators and open-ended stubs. The center frequencies are 1.8 GHz and 2.1 GHz. A transmission zero is designed at the frequency point of 2.1 GHz in the 1.8 GHz filter. Direct input feeding is employed, achieving an isolation greater than 50 dB between the two filters. The second circuit adds an additional filter with a center frequency of 1.5 GHz to the existing circuit. A transmission zero is designed at the frequency point of 1.8 GHz in this filter. Finally, it is combined with other filters to form a triplexer. The isolation between all filters is greater than 50 dB. However, this thesis focuses on the T-shaped direct input feeding method, making the design and adjustment of the input impedance for each filter crucial.
