A compact bandpass filter using a 1-D periodic slow wave structure

A compact, dual-mode bandpass filter based on a stripline ring resonator is presented. This 2-pole filter was implemented using a one-dimensional periodic structure, such that the physical length of the ring resonator was decreased due to the slow wave effect. At a center frequency of 2 GHz, the length of the ring was reduced by 41.8%, and the overall footprint of the filter was reduced by 51.9%. With the periodic structure, this filter achieved 0.6 dB of loss centered in a 310 MHz bandwidth, compared to 1 dB of loss centered in a 230 MHz bandwidth achieved without the slow wave structure.