An aerial designed for direction-finding use and normally used in airborne direction-finding equipment. A vertical polarized radio wave incident upon the loop induces voltage in the vertical members of the loop. The signal-induced voltage will vary between the two members, depending on the loop's angle to the transmitted signal. It is minimum when the loop is at a right angle to the incoming signal and maximum when the loop is in line. Thus, given the rotation of the loop and arriving at a zero differential (null point), the direction of the incoming signal can be found although there is a 180° ambiguity. This is removed by superimposing a signal on the loop aerial by a vertical, or sense, aerial. As airborne equipment, a loop aerial may be fixed with the centerline of the aircraft and used with a homing receiver, or it may be capable of being rotated for direction finding.
