A wideband multilayer tunable filter using active frequency selective surface

A wideband multilayer filter with frequency tunable characteristics is proposed using active frequency selective surface (AFSS). The proposed AFSS includes three metal layers, while the top and bottom metal layers are embedded with varactors. The metal layers are separated by dielectric layers. By simultaneously adjusting the bias voltage loaded on both ends of the varactor diode, the working bandwidth of the AFSS can be continuously tuned. The operating mechanism is studied using an equivalent circuit, which is composed of an LC series resonance circuit and a parallel resonance circuit. The simulation results prove that the proposed AFSS performs wideband filtering in the frequency range of 3.55 to 4.43 GHz without a bias voltage. With a bias voltage of -19 V, the AFSS working passband is tuned to 4.43 to 5.53 GHz. Simulation and experimental results show that the AFSS has wideband filtering characteristics and good tunable performance.