Author: Edmund A. Laport
Directive antennas for use on the low frequencies are limited to those which function with electrically close spacing. For receiving, the loop antenna giving a figure-of-eight pattern, and the loop, in conjunction with a vertical sense antenna, giving the cardioid pattern, has long been used for direction finders particularly. The cardioid pattern from a loop and a vertical antenna is obtained by phasing the current in the latter at 90 degrees with respect to that in one side of the loop and by carefully balancing their relative current amplitudes to obtain the full null of the cardioid. This principle is amply described in all radio textbooks, particularly those dealing with direction finding. Ships and aircraft continue to be the principal users of direction finders as navigational aids. In recent years, the automatic direction finder has been developed to indicate continuously the bearing of the station used as the beacon. However, the use of loops for fixed point-to-point services has been marginal and of small importance.