Electrically-small TE01 mode spherical wire antennas employing lossy magneto-dielectric materials

It well-known that a spherical wire antenna designed to radiate solely the TE₀₁ mode exhibits higher radiation Q than does one designed to radiate solely the TM₀₁ spherical mode, when both are unfilled and of the same size. Introduction of a magnetic core into a TE₀₁ mode spherical wire antenna is known to reduce the radiation Q by reducing the magnetic energy stored in the interior of the sphere, although only to a certain extent depending on the electrical size of the sphere. Here we examine the case of a lossy magneto-dielectric core. We show that even when the magnetic material exhibits significant loss, the performance of the antenna in terms of its gain including radiation efficiency is still greatly improved. Even in the hypothetical case in which the loss tangent tends to infinity, the efficiency of the antenna can still be quite large. In fact, the use of a ferrite which is predominantly lossy avoids the detrimental effect of internal modes in the spherical volume. However, the dielectric behavior of a magneto-dielectric core has a detrimental effect of on both radiation efficiency and radiation Q. We examine specific cases involving commercially available ferrite materials. The detrimental effect of the dielectric polarizability essentially precludes the use of so-called broadband, high impedance Mn-Zn ferrites.