Bandpass filter using microstrip ring resonators

Abstract

A new ring resonator with enhanced coupling is proposed. For a 5.2 GHz resonator, |S21| of the second resonant mode is 12 dB below that of the first mode. Based on this new structure, a bandpass filter is constructed. The insertion loss is 0.2 dB better and out-of-band suppression at 150 MHz offset is 7 dB better than those of the generic coupled-line filter and the size is 21% smaller.