Novel Dual-band Bandpass-to-Bandstop Filter Using Shunt PIN Switches Loaded on the Transmission Line

A novel method to design the bandpass-to-bandstop (BP-to-BS) filter is presented in this paper. This method demonstrates that using shunt switches to select bandpass or bandstop mode does not deteriorate the passband insertion loss (IL) in the bandstop mode. On the basis of this mechanism, a dual-band BP-to-BS filter was designed, fabricated and measured. The filter consists of two pairs of stepped impedance resonators with mixed electric and magnetic coupling, resulting in dual bands for each filter configuration. In the bandpass mode, five transmission zeros (TZs) are generated which substantially enhances the filter selectivity. The generation of these TZs is carefully studied. Their positions could be easily controlled by changing the coupling magnitude. In the bandstop mode, the filter also demonstrates high selectivity with five transmission poles. Large in-band rejection and low passband IL are achieved simultaneously. The in-band rejection is beyond 30dB and 40dB for the first and second stopband, respectively. As for passband IL, the measured minimum passband IL is 0.34 dB. The measured and simulated results are in good agreement for both the bandpass and bandstop modes, achieving excellent dual-band reconfigurable filtering performance.