本論文提出一以微帶線(microstrip)實現之雙模(dual-mode)微波帶通濾波器(bandpass filter,BPF),該濾波器同時具備中心頻率可調與頻寬可控制之特性。此可調式濾波器以Y型微帶線結構為主體搭配四組可變電容二極體進行模態微擾(mode perturbations)。其中,偶模態與奇模態之共振頻率可藉由可變電容獨立控制以達到通帶之可重組性(reconfigurability)。經由實作與量測驗證,本文提出之雙模帶通濾波器在通帶中維持相同漣波高度(15dB)的情況下,具有中心頻率49%之可調範圍與300%之頻寬控制性。
A varactor-tuned dual-mode microstrip bandpass filter with tunability of passband ripple, bandwidth, as well as center frequency is proposed. The proposed tunable filter comprises a Y-shaped microstrip-line structure connected with four varactor diodes for mode perturbations. Specifically, the even- and odd-mode resonances attributed to the filter passband reconfigurability are able to be separately adjusted via the incorporaterd varactor diodes. As a result, the proposed dual-mode bandpass filter exhibits a up to 49% center frequency tuning range together with a 300% passband bandwidth tunning capability with unchanged ripples(15dB).