Achievable bandwidth of a quarter wavelength side-coupled ring resonator

Studies on the achievable range of bandwidth of a side-coupled ring resonator bandpass filter are presented. The elements of the resonator susceptible on varying the filter bandwidth are identified and design solutions are given in order to push the bandwidth to its minimum and maximum values. Based on the side-coupled ring resonator topology, two microstrip filters were designed at 10 GHz to achieve the narrowest and widest bandwidth with respect to insertion losses and technological limitation. Results of the studies with the given technology show that the ring resonator is suitable to address bandwidth from narrow (3.6%) to wide (31%). These concepts are validated through simulations and experiments for filters implemented on alumina substrate.