Microwave circuit theory-based models to predict the resonant frequencies of a wide range of ring resonators

The concept of the ring resonance of a symmetric two-port network is used to determine the resonant frequencies of a variety of ring resonators, on the basis of simple transmission-line or coupled-transmission-line equivalent circuits. Several illustrative structures, from the closed ring microstrip to the Pendry-type split-ring slotline resonators, have been analysed and measured. Full-wave simulations and measurements are in excellent agreement with the proposed models, and even with its short-line approximations, when suitable.