The Excitation of Surface Waves by a Vertical Antenna

The excitation of surface waves by a vertical, linear antenna erected on an infinite, flat, perfectly conducting image plane coated with a thin layer of dielectric is investigated theoretically. Helmholtz-type integral expressions, derived through the use of the results of a previous paper, are utilized in the computation of numerical data. The appendix is devoted to the development of an approximate current distribution for the antenna. The far-zone fields for the configuration are composed of two types of waves-the radiated wave, a wave of spherical type, and one or more surface waves, waves of cylindrical TM type which attenuate exponentially with height above the dielectric surface. The theoretical magnitudes of these two are combined to yield field patterns that show the large magnitude of the surface-wave component excited by the vertical antenna. The experimental approximation to the configuration consisted of a large ground plane enclosed by a microwave dark room. The experimental data, in addition to being presented so as to verify the theory, were replotted in a form that yields convenient design curves for surface wave antennas of this type. Additional measurements were taken over partially coated surfaces to aid in both the understanding of the phenomenon and its practical application to directive radiators.