An efficient analysis of vertical dipole antennas above a lossy half-space.

摘要

The electromagnetic modeling of radiation by vertical dipole antennas above a lossy half-space has become an important subject due to many applications where these dipoles are involved. The modeling often encounters Sommerfeld-type integrals that are normally highly oscillatory with poor convergence. Recently, an efficient computation of the electric field radiated by an infinitesimal electric dipole above a lossy half-space has been reported, in which the Sommerfeld-type integrals are reduced to rapidly-converging integrals. Taking advantage of such efficiently-calculated electric field and using it as the Green's function, in this thesis, an electric field integral equation (EFIE) is formulated for the analysis of a vertical dipole antenna above a lossy half-space. Then, the EFIE is solved numerically employing the Method of Moments (MoM). Sample numerical results are presented and discussed for the current distribution as well as the input impedance and radiation pattern of a vertical thin-wire antenna above a lossy half-space. First, the EFIE solutions of the current distribution on an antenna in free space are compared with that obtained using a traditional approach of solving the Pocklington's equation, and a good agreement is observed. Then, the current distributions on an antenna above a lossy half-space of various conductivities are compared with that for the antenna above a PEC plane. The comparison illustrates that as the conductivity increases, the current distribution gradually approach to, and finally match that for the antenna above a PEC plane, as one would expect. Data of the current distributed on an antenna above a lossy half-space at different heights show that for an antenna close to the media interface separating two half-spaces, the lower half-space can significantly affect the current distribution on the antenna and its input impedance. But as the antenna is located farther apart from the media interface, the influence of the lower half-space would become weaker and weaker, and eventually negligible. The radiation patterns of an antenna above a very lossy half-space and that for an antenna at different heights above a lossy half-space are also presented. They exhibit properties as expected and similar to that documented in literature for infinitesimal vertical dipoles above a lossy half-space.