Switchable Dual-Band Bandpass Filter with High Selectivity

In this paper, a novel switchable dual-band bandpass filter (BPF) with high selectivity is proposed. Half wavelength resonators and open stub loaded resonators are employed to provide third-order filtering responses in each band. By utilizing stepped-impedance open stubs and one-end-shorted couple lines, the individual passband signal can be suppressed independently with switches. In addition, the proposed coupling topology introduces multiple transmission zeros providing high frequency selectivity and good out-of-band rejection. The proposed switchable filter is implemented with two passbands centered at 2.90GHz and 4.79GHz with a low insertion loss of 1.2 dB and 1.1 dB, respectively, providing band-edge steepness over 97.7 dB/GHz. Four operating modes (dual-band, no band, high band, and low band) are achieved by controlling the states of passbands with switches.