Theoretical and experimental characterization of Q-factor in trapped-mode metamaterial cells

The electromagnetic response, power distribution, and coupling-induced energy exchange processes are analyzed in two coupled microwave resonator systems. The first system comprises two split-ring resonators, while the second consists of a microstrip and a dielectric resonator combination. The results demonstrate that coupled two-resonator systems with typical electrical parameter values exhibit a pronounced nonlinear Fano response, accompanied by substantial enhancements in quality factor and group delay relative to their individual constituent resonators. This enhancement occurs under conditions of Fano resonance, which is associated with the excitation of a trapped mode. The SRR–SRR system operates at ∼3.88 GHz, with individual resonator Q-factors of 143–191, achieving a Q-factor of 2100 under Fano resonance conditions. The MSR–DR system operates at ∼4.25 GHz, with individual Q-factors of 154 and 1310 for the MSR and DR, respectively, reaching a Q-factor of 28 000 in the Fano resonance regime. In this regime, the incident power is efficiently confined and circulates between the resonators, leading to high stored electromagnetic energy and a suppression of losses caused by radiation. The observed anomalous characteristics are not attributable to the intrinsic properties of the individual resonators but rather arise from the specific energy exchange mechanisms that generate non-radiating trapped modes. Electromagnetic structures capable of such efficient power confinement and high Q-factors hold potential applications in microwave absorption, sensing, and the generation of frequency-stable signals with low phase noise levels.