Quasi-elliptic dual-band stepped-impedance filters with folded parallel high-impedance segments

A design approach is presented for dual-band filters formed by cascaded stepped-impedance resonators in microstrip technology. The resonators feature folded parallel highimpedance sections which permit resonator coupling in cascaded arrangements and, at the same time, create transmission zeros between the two passbands. Additional transmission zeros in the lower and upper frequency ranges are created by employing source-load coupling. All designs are verified by results obtained from two different commercially available field solvers.