Compact microstrip lowpass filter with ultra-sharp roll-off and ultra-wide stopband using stepped impedance Hairpin resonator

A novel microstrip lowpass filter (LPF) with very sharp roll-off, compact size and ultra-wide stopband is presented in this paper. The structure consists of modified stepped impedance Hairpin resonator and a circular patch as a suppressor. The proposed LPF has the cut-off frequency of 1.07 GHz. The simulation results indicated that the transition-band of the proposed LPF is 0.09 GHz from −3 to −20 dB. Maximum insertion-loss at about 80% of the passband is 0.1 dB. The proposed LPF has been designed, fabricated and measured. From the measurements, good agreements with the simulated results are obtained. Also, an ultra-wide stopband was achieved. Proposed LPF has an ultra high figure-of-merit (FOM) of 151,523, which shows its strong efficiency.