Ring resonator based bandpass filter enabling enhanced sideband suppression

A microstrip filter based on a single-ring Bandpass section integrated with a band-trimming section incorporating two cascaded rings was demonstrated featuring enhanced suppression. The stop-band for the input bandpass section could be selectively eliminated via the proposed band-tailoring section without causing any excessive loss, thereby improving the overall transmission of the device with regard to higher suppression, sharper roll-off and narrower bandwidth. For the completed device with the center frequency at 4 GHz, the suppression ratio was increased by ~8 dB, the 3-dB bandwidth was reduced from 98 MHz to 48 MHz with negligible excessive loss, and the filter quality factor was elevated by about 105%.