Subwavelength microwave resonators exhibiting strong coupling to radiation modes

We demonstrate a subwavelength spherical resonator at microwave frequencies designed to mimic the electromagnetic behavior of a negative permittivity sphere. The structure, which has a radius of similar to lambda/12 (where lambda is the resonant wavelength), consists of an axially symmetric array of noninterconnected conducting elements forming a resonant spherical object. The structure exhibits many of the properties inherent to negative permittivity spherical resonators, the most notable being a very strong coupling to radiation modes despite being much smaller than the wavelength. This characteristic is quantified by the radiation Q-factor, which was observed to be near 1.5 times the theoretical limit in some of the measured samples, matching the performance achievable in a negative permittivity sphere of comparable electrical size. These resonators may find application in the design of electrically small antennas, as well as in the experimental ``simulation,{''} at microwave frequencies, of nanophotonic device concepts based upon localized plasmon resonances in metal nanoparticles. (C) 2005 American Institute of Physics.