Non-uniform DGS low pass filter with ultra-wide stopband

New low pass filters with ultra-wide stopband by using dumbbell defected ground structures (DGSs) with size reduction are presented in this paper. Non-uniform DGSs etched under a stepped-impedance microstrip line are developed to get better filter performances of transmission zeros, enhanced return loss and ultra-wide stopband that is beneficial to higher order harmonic suppression. A comparison of low pass filters between standard 50-ohm microstrip line and stepped-impedance microstrip line has been evaluated, respectively. The proposed low pass filter with non-uniform dumbbell DGSs and stepped-impedance microstrip line has better performances than that with uniform DGSs and uniform microstrip line, and simultaneously, DGS units are decreased and which brings a smaller circuit size. The design is demonstrated by measurement.