A tri-section stepped impedance bandpass filter with harmonic suppression

Abstract

A compact microstrip bandpass filter with harmonic suppression is presented in this letter. The filter is composed of two tri-section stepped impedance resonators cascaded and two end-open L-shaped microstrip lines for the input and output feed lines. The harmonic suppression of the bandpass filter may be realized by choosing proper lengths for the L-shaped microstrip lines and proper impedance ratios of the stepped impedance resonator. The filter has been investigated numerically. Simulation results show that the second-order harmonic response is effectively suppressed, and the rejection level is kept below -19 dB.