TEM Field Structure of Electric and Magnetic Fields From a Semi-Infinite Vertical Thin-Wire Antenna Above a Conducting Plane

Abstract

Investigation is carried out on the electric and magnetic field structures around a semi-infinite thin-wire antenna vertically placed above a perfectly conducting ground plane. It is shown that the electric and magnetic fields due to a time-varying point source at the bottom of the antenna have a field structure identical to that for the case of a uniform line charge and a uniform current, and have a spherical transverse electromagnetic (TEM) field structure. Simple, but exact, expressions for the electric and magnetic fields are derived, and it is shown that the general expressions for the electric and magnetic fields from time-varying sources on a thin wire semi-infinite antenna reduce to the same simple expressions if the source is assumed to be a current or charge pulse traveling at the speed of light and without attenuation. In that case, the Poynting vector indicates energy flow in the radial direction from the source at the bottom of the antenna. That is, in this ideal case the only source of radiation is the point source at the bottom of the antenna and the vertical antenna itself does not radiate. The wave impedance at all distances from this antenna is the free space impedance. Further, a general discussion on the TEM type solutions in different structures containing two perfect conductors is provided.