Compact 2.4-/2.9-GHz band parallel-planar bandpass filter

This paper proposes a compact dual-band bandpass filter (DBPF) based on a parallel-planar architecture where resonators are formed on the opposite sides of each substrate. The proposed architecture enables dual-band operation without an appreciable change in the volume of the DBPF and yields design freedom for the resonant frequencies by adjusting the distance between the substrates. A 2.4-/2.9-GHz band DBPF is fabricated using YBCO film deposited on a MgO substrate with a coplanar waveguide structure to investigate experimentally dual-band operation. The measurement results agree with those of the simulation.