Improved method of adjustment of medium-wave directional-antenna systems

An improved method is described for adjusting medium-wave directional-antenna systems containing high radiators (of the order of ¿¿). It is pointed out that the determination of radiator driving-point impedances corresponding to the desired radiation pattern requires special consideration; namely, the radiation pattern determines the relationship between radiator currents near the current maximum, and not that between those at the base which is necessary for the calculation of driving-point impedances. It is shown that the two sets of current relationships may differ considerably. Since no reliable data for current distribution along high radiators in an array exist, an experimental method is proposed for obtaining the correlation between the two sets of current relations. Radiator driving-point impedances can then be calculated on the basis of circuit theory, the relationship found between currents at the radiator bases (corresponding to the desired radiation pattern), and the measured values of self and mutual impedances. For practical reasons, the method is limited to a few simple, but important, arrays. In order to avoid the usual lengthy trial-and-error method, the adjustment of the feeder system with dummy loads instead of the radiators is recommended, with the impedances of the dummy loads corresponding to the calculated driving-point impedances of the radiators.