Double half-ring resonators for bandpass filter applications with suppression of multiple harmonics and size reduction

Ring resonators have been widely used for various applications. In this paper, double half ring resonators working at 2.5GHz are proposed for bandpass filter applications. These resonators suppress multiple harmonics (2^nd and 3^rd harmonics) and provide size compactness with employing various physical configurations. Conventional circular ring resonators are modified to be transformed to new forms holding double half ring configurations. A closed loop split ring resonator and open loop double half ring resonators are compared to decrease the resonant frequency. Continuously, the open double half ring resonator adds open microstrip lines to additionally reduce the resonant frequency. Open loop structure provides flexible design and lower resonant frequency, in other words, reduction of real estate. 4 different simulated resonators are fabricated and measured. They show very high quality factor and suppression of multiple harmonics.