PERFORMANCE OF AN ARRAY OF VERTICAL DIPOLES OVER AN INHOMOGENEOUS GROUND SYSTEM

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The elevation radiation patterns of a stacked array of vertical electric dipoles (VEDs) over several different azimuthally symmetric inhomogeneous ground systems are studied using an integral formulation. As the ground influences the pattern of each VED differently, there is no known optimum array excitation which can be used to achieve desired beam shaping and steering. Patterns in an array of 21 VEDs spaced 0.1 lambda apart are computed and compared to HF (10 MHz) for three excitation functions: (a) conventional linear spacial phasing, (b) phasing according to the complex conjugate of the field produced by each VED in the direction of steering, and (c) spacially sinusoidal excitation with constant phasing. Results are given for grounds consisting of homogeneous earth, a perfectly conducting ground plane, a perfectly conducting disk on homogeneous earth and 2 lambda long radial wire ground systems on well- and poorly-conducting earth. It is found that the radiation pattern cannot be steered below about 9/sup 0/ in elevation for any of the excitation functions or the ground systems used. For low-angle steering conjugate excitation produces a slightly narrower beam with smaller sidelobes. Highly conducting grounds tend to permit steering to slightly higher elevations with narrower beams.