Quality Factor and Radiation Efficiency of Dual-Mode Self-Resonant Spherical Antennas With Lossy Magnetodielectric Cores

For spherical antennas consisting of a solid magnetodielectric lossy core with an impressed surface current density exciting a superposition of the TEmn and TMmn spherical modes, we analytically determine the radiation quality factor Q and radiation efficiency e. Also, we determine the relative mode excitation, as a function of the core material parameters, which ensures self-resonance. For the specific case of a dual- TEm1, TMm1 dipole antenna of half a wavelength circumference, we show quantitatively, how Q/e and e behave, and can be optimized as functions of permeability and magnetic loss tangent. We obtain Q/e values well below the Chu lower bound with fair efficiencies up to 71% - 84%.