Excitation of the Zenneck Wave by a Tapered Line Source

A Zenneck wave is a "nonphysical wave" that propagates on a semi-infinite 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 out to some distance. The taper can also be chosen to optimize the field at a given distance from the source on the surface of the earth, leading to what is called an "optimum" line source. The optimum line source can be used to produce a field along the surface of the earth that is nearly constant over a large range of distances.