Design of a dual band-pass filter using modified folded stepped-impedance resonators

A folded stepped impedance resonator (SIR) modified by adding an inner quasi-lumped SIR stub is used as the basic block of a new configuration of dual band-pass filter. The main advantage of the proposed filter is to allow independent control of the features of the first and the second pass bands. Additional design flexibility can be achieved by allowing the stub to be located at an arbitrary position along the high impedance line section of the main SIR. The positions of the tapped lines have been optimized in order to match the filter at the central frequencies of both pass bands. Some designs are reported to illustrate the possibilities of the structure.