Efficiency of surface wave excitation

The excitation efficiency of surface waves is the ratio between the power in an open-waveguide mode and the total power available at the feed. It should be maximized if the open waveguide is used as a transmission line; and it should be a predictable quantity if the guide is used as an antenna whose pattern is to be modified in some specified manner by the feed radiation. A method based on Fourier transforms is used to calculate the excitation of surface waves by arbitrary sources. The chief result is that the amplitude of excitation is proportional to the gain of the source in free space in the complex direction that corresponds to the propagation constant of the surface wave. Some of the predictions have been verified experimentally.