Top-coupled parallel-cascaded ring filter with transmission zeros

A pseudo-elliptic bandpass filter based on two top-coupled parallel-connected ring resonators is presented. Each ring contributes to the creation of two (2) poles leading to a 4^th order response of the filter. Based on the topology, two (2) transmission zeros are obtained at both sides of the passband, ensuring the high selectivity of the filter. Centered at 2 GHz with 15% relative bandwidth a proof of concept of the compact filter topology is realized by using microstrip lines on epoxy glass substrate. The filter layout is presented in this paper along with the comparison between the simulation and measurement results.