Individually controllable dual-band bandpass filter with multiple transmission zeros and wide stopband

Abstract

In this paper, a compact dual-band bandpass (DB-BPF) with multiple transmission zeros and wide stopband is developed. The DB-BPF consists of a pair of open-ended stub-loaded short-circuited stepped-impedance resonators with easy control of their two fundamental resonant modes. Moreover, multiple geometrical parameters in both the external feeding structure and the internal couplings between neighboring resonators are employed to make the individual control of the two passbands possible. Furthermore, the introduced multiple coupling paths between the resonators produce transversal signal interference which creates multiple transmission zeros. As a result, the selectivity of the passbands is improved significantly, and the stopband of the filter is extended greatly. A DB-BPF with center frequencies of 1.5 GHz and 3.65 GHz, and fractional bandwidths (FBWs) of 5% and 3% is fabricated, and its measured response agrees well with the predicted one.