Switchable bandpass filter with two-state frequency responses

A novel switchable bandpass filter with two-state frequency responses is presented, where dual-band bandpass and single bandpass characteristics can be conveniently switched by turning pin diodes on and off. The switchability results from the effect of different working modes. The filter can work as a dual-band bandpass filter obtaining two centre frequencies, 1.8 and 3.5 GHz, which could be appropriately used for GSM and WiMax systems. In the meantime, it also can operate only at 3.5 GHz, rejecting signal at 1.8 GHz. The proposed filter consists of two dual-mode resonators, using pin diodes to switch the frequency responses. An experiment was carried out to validate the design concept, and the measured results agree well with simulated results.