Microstrip lowpass filter with high and wide rejection band

A miniaturised lowpass filter with sharp roll-off and wide stopband using radial split ring resonator loaded by folded polygon patches is proposed. Multiple transmission zeros by different resonator due to different attenuation poles in the stopband region is created. A wide stopband and sharp frequency response are obtained in the stopband region. The proposed filter has 3 dB cut off frequency at 1.76 GHz, and the stopband region with the attenuation level better than 23 dB is extended from 2.06 up to 18.83 GHz. The roll-off rate of the proposed filter is 94.9 dB/GHz and, finally, the proposed filter has a high figure of merit equal to 27292.