Excitation of the Zenneck Wave by a Tapered Line Source Above the Earth or Ocean

A tapered vertical line source over the surface of the earth or ocean is explored as a means of communication. Two types of tapers for the line source are explored. One is a “Zenneck-wave” taper and the other is an “optimum” taper. The Zenneck-wave taper is chosen to excite the Zenneck wave to the extent possible. The Zenneck wave is a “nonphysical wave” that propagates on a semiinfinite lossy earth. The wave is nonphysical in the sense that a simple source such as a dipole will not excite a field that resembles the Zenneck wave at large distances from the source. However, by using a tapered line source, a field that resembles the Zenneck wave can be produced along the surface of the earth or ocean out to some distance. The optimum taper is chosen to optimize the field at a given horizontal distance from the line source on the surface of the earth or ocean. The optimum line source can be used to produce a field along the surface of the earth or ocean that is nearly constant over a large range of distances, something that does not seem easily attainable with other types of sources.