Minimum Q circularly polarized electrically small spherical antennas

The radiation problem for the TM₁₀- and TE₁₀-mode electric current densities on the surface of a spherical magnetic coated PEC core is solved analytically. The combination of the electric and magnetic dipole modes reduces the radiation Q of the antenna. Moreover, with an appropriately designed magnetic-coated PEC core the stored energies of these modes balance each other making the antenna self-resonant and at the same time ensuring a perfect circularly polarized radiation. Numerical results for a practical dual-mode electrically small antenna confirm the theoretical predictions. A 4-arm spherical helix antenna with a magnetic-coated PEC core radiating both TM₁₀ and TE₁₀ spherical modes exhibits a perfect circular polarization in almost all directions. The antenna is self-resonant with the radiation Q being 0.67Q_Chu, or 1.27Q_dual.