Sharp-rejection broadband microstrip bandpass filter using penta-mode resonator

A broadband microstrip bandpass filter using a stub-loaded resonator is proposed. The basic block of the proposed filter is a penta-mode resonator that consists of a stepped-impedance resonator and a shunt open-circuited stub. The shunt stub not only increases the passband bandwidth but also creates two transmission zeros for a sharp cutoff response at both the lower and upper stopbands.