Compact quint-band microstrip bandpass filter using double-layered substrate

A quint-band bandpass filter using double-layered substrate is proposed. The basic components used to build the proposed filter are three pairs of microstrip stepped-impedance resonators on the top and middle metal layer, and two pairs of slot uniform-impedance resonators on the bottom metal layer. Since each pairs of resonators control a respective passband, the proposed design is flexible and features a high design freedom. The proposed filter has the advantages of compact size and sharp passband selectivity. Due to crossed coupling, the transmission zeros at the both sides of the passbands enhance passband selectivity.