Realization of a Non-radiating Electromagnetic source using a Trapped Mode Resonator

This paper examines the development of a non-radiating electromagnetic source that utilizes the concept of ”trapped mode” resonance in a one-dimensional (1D) periodic structure within the microwave frequency range. The periodic structure comprises a ground-backed, dielectric-loaded metallic patch with embedded shorting pins located at two corners. This design exhibits a narrow electromagnetic bandgap with a bandgap to center frequency ratio Δf/f0 ≈ 4.99% , which results in strong group velocity dispersion and a slowdown of electromagnetic waves, hence demonstrating trapped mode resonance. The unit cell structure is ultimately transformed into an electromagnetic source, resembling an antenna, where trapped mode resonance is excited on a single resonator using a microstrip transmission line. This configuration generates horizontal magnetic loop currents that create tightly confined electric field distributions within the metallic plates while maintaining a low radiation efficiency of around 9% at resonance. Our conclusions stem from multipolar scattering analysis, which extended to the magnetic quadrupole, as well as from full-wave electromagnetic simulations and the Finite Difference Time Domain (FDTD) method. Lastly, we validated our results through microwave measurements carried out in an anechoic chamber using a vector network analyzer.