Approaching the Lower Bounds on Q for Electrically Small Electric-Dipole Antennas Using High Permeability Shells

We study the effect of surrounding electrically small, top-loaded, electric-dipole antennas with a thin shell of high-permeability magnetic material. The magnetic polarization currents induced in the thin shell of magnetic material reduce the internal stored energy, resulting in a lower as compared to conventional designs. The simulated ´s of thin-magnetic-shell cylindrical and spherical antennas are compared to recently derived lower bounds on . The high permeability shells reduce the of these antennas to values below the lower bounds for purely global electric current sources. In the case of the spherical electric-dipole antenna, a sufficiently large value of permeability enables the to be reduced to a value that is only 1.11 times the Chu lower bound.