On the effect of a spherical shield on the radiation Q and efficiency of ideal dipole antennas

摘要

A method is developed for calculating the radiation efficiency and quality factor, Q, for azimuthally symmetric electric (TM) and magnetic (TE) multipole fields surrounded by a semi-transparent spherical shield of variable thickness, dielectric and magnetic constants involving losses. A matrix method is used to connect the transverse field components at adjacent interfaces. The Q and efficiency are determined by computing the energy stored in the near field of the multipole as well as the power radiated and dissipated in the shield. A numerical comparison of the performance of electric and magnetic dipole radiators is given as a function of frequency. An expression is derived for the permittivity of the shield which optimises the Q.