Independently Tunable Dual-Band Bandpass Filter

A reconfigurable multiband band-pass filter is proposed in this paper, using the structures and techniques of the Stub-loaded Stepped-Impedance Resonators dual-mode configuration. This design uses the source-load link and the shorted T-shaped stub lines. The proposed structure has the advantages of compact size, high selectivity, and a single control bias voltage applied. Four adjustable transmission zeroes were attained by the suggested filter, with more than 40 dB rejection between the two passbands. Employing the coupling paths effectively yielded the independent control of the two passbands. For the purpose of tuning, two identical varactor diodes were loaded onto the open ends of the resonators. A frequency tuning range of 1.08 GHz to 1.5 GHz and 1.99 GHz to 2.7 GHz is achieved in the two passbands respectively. The designed filter realized an insertion of 1.2 dB to 1.32 and 0.86 dB to 1.11 dB respectively in the tuning process. The overall filter size of 0.13λ
₀
× 0.03λ
₀
is achieved.