Design of compact ultra wide-stopband lowpass filter

For miniaturization and harmonic suppression, a novel planar compact lowpass filter is presented in this paper. A conventional stepped-impedance lowpass filter is modified by some microstrip steps connected in 90 ° and some T-shaped transmission lines integrated into the lowpass filter. The proposed lowpass filter has the advantage of low insertion loss (below 0.4 dB at 0~2 GHz), ultra wide stopband (over 20 dB at 3~9 GHz) and compact size. Experiment validates the design concept.