Electrically small circularly polarized spherical antenna with air core

An electrically small circularly polarized self-resonant spherical antenna with air core is presented. The antenna is a modified multiarm spherical helix exciting TM₁₀ and TE₁₀ spherical modes with equal radiated power, and thus yielding perfect circular polarization over the entire far-field sphere (except the polar regions, where the radiation is low). The self-resonance is achieved by exciting higher-order TM modes, which provide the necessary electric stored energy in the near-field, while contributing negligibly to the far-field radiation of the antenna. The antenna has electrical size ka = 0.254, and its radiation quality factor Q is 1.76 times the Chu lower bound.