Switchable Dual-Band Filter With Common Quarter-Wavelength Resonators

This brief presents a compact switchable dual-band filter with four operating states. The filter is established by adding switching circuits to a concurrent dual-band filter. The original concurrent dual-band filter has hybrid coupling paths and uses two stepped-impedance quarter-wavelength resonators that are shared by the two passbands, so fewer resonators are required. In addition, the central frequencies and bandwidths of the two desired passbands can be separately designed without time-consuming trial and error. Two types of switching circuit are added to the original concurrent dual-band filter to obtain a switchable dual-band filter. The switching mechanisms are analyzed and discussed. The proposed switchable dual-band filter has four possible operating states, so the two passbands can be activated or deactivated independently. The simulated and measured results verify the performance of the proposed structure.