Compact microstrip triple-mode filter based on stepped-impedance resonators

In this paper, a compact S-band microstrip triple-mode bandpass filters with good out-of-band rejection performance is presented. The proposed triple-mode filter supports three transmission poles and two transmission zeros and it is designed by the half-wavelength microstrip line. The filter is composed of two T-shape resonators, which control out-of-band transmission zero position. For saving design space, this filter uses the stepped-impedance resonator (SIR) to arrive the purpose. Finally, experimental performance data are shown to be in close agreement with the design data.