Near Chu-limit Performance in Electrically Small Antennas Based Upon Metamaterial Spherical Resonators

We present the design, fabrication, and experimental characterization of a new class of electrically small antennas whose bandwidth performance approaches the Chu limit. The antennas are based upon recently reported spherical microwave resonator structures (H.R. Stuart and C. Tran, Appl. Phys. Lett. Vol. 87, 151108, 2005). The resonators consist of an axially symmetric periodic array of printed circuit boards (PCBs), each containing identical split-ring patterns, assembled to form a resonating spherical object. The resonators were designed to mimic the electromagnetic behavior of the negative permittivity sphere. It has been shown that an electrically small negative permittivity sphere is characterized by a Q-factor that is 1.5 times the Chu limit (H.R. Stuart and A. Pidwerbetsky, IEEE APS International Symposium, 2005, paper 9.7), Scattering measurements of the microwave resonators forming the basis of these antennas confirm that 1.5x Chu limit behavior can be achieved experimentally in these structures.