The Beverage wave antenna: Radiation field patterns

This report presents the results of a theoretical and experimental investigation of the transmitting and receiving properties (far-field radiation patterns) of horizontal-wire antennas placed over an imperfectly conducting halfspace. Particular emphasis is given to the Beverage Wave Antenna, a special type of horizontal-wire antenna placed in close proximity to the earth. Early work by Sommerfeld showed that the radiation from a dipole above an imperfect earth could be separated into a space wave (which could reflect off the ionosphere and which predominates at large distances above the earth) and a surface wave (which could diffract around the curvature of the earth and which dominates close to the surface). Because of the difficulties involved in solving the Sommerfeld integral formulation, asymptotic approximations valid in the radiation zone have generally been employed to solve this problem. The useful approximate forms developed earlier by Norton have been used in this study, the only difference being that in the present analysis the exact expressions for the antenna current are used rather than an assumed current distribution. An expression for the space-wave radiation pattern is formulated using a 'geometric optics' approximation, while the superposition principle is used to sum the fields of individual infinitesimal dipoles to obtain the surface-wave radiation pattern. Expressions for a number of useful antenna parameters (efficiency, front-to-back ratio, antenna gain, effective length) are then derived.