being due to a classical current through a wire, in this case the currents in the conductor itself are much smaller, with the energy transmitted in the form of an electromagnetic wave (radio wave). But in this case, the presence of the wire acts to guide that wave toward the load, rather than radiating away. The reduction of ohmic losses compared to using coax (or other two-wire transmission lines) is especially an advantage at higher frequencies where these losses become very large. Practically speaking, use of this transmission mode below microwave frequencies is very problematic due to the very extended field patterns around the wire. The fields associated with the surface wave along the conductor are significant out to many conductor diameters, therefore metallic or even dielectric materials inadvertently present in these regions will distort the propagation of the mode and typically will increase propagation loss. Although there is no wavelength dependence to this dimension in the transverse direction, in the direction of propagation it is necessary to have a minimum of one half wave of conductor length to fully support the propagating mode. For these reasons, and at frequencies available prior to about 1950, the practical disadvantages of such transmission completely outweighed the reduced loss due to the wire's finite conductivity. Goubau line In 1950 Georg Goubau revisited Sommerfeld's discovery of a surface wave mode along a wire, but with the intent of increasing its practicality. One major goal was to reduce the extent of the fields surrounding the conductor so that such a wire would not require an unreasonably large clearance. Another problem was that Sommerfeld's wave propagated exactly at the speed of light (or the slightly lower speed of light in air, for a wire surrounded by air). That meant that there would be radiation losses. The straight wire acts as a long wire antenna, robbing the radiated power from the guided mode. If the propagation velocity can be reduced below the speed of light then the surrounding fields become evanescent, and are thus unable to propagate energy away from the area surrounding the wire. Goubau investigated the beneficial effect of a wire whose surface is structured (rather than an exact cylinder) such as would be obtained using a threaded wire. More significantly, Goubau proposed the application of a dielectric layer surrounding the wire. Even a rather thin layer (relative to the wavelength) of a dielectric will