Directive gain and impedance of a ring array of antennas

Ring arrays can be made so that they concentrate the radiated power in the plane of the ring and are also omnidirectional (or nearly so) in this plane. This paper deals with ring arrays which exhibit these properties. For antenna lengths which are equal to and less than
\lambda/4
, graphs are included which show, or make it easy to calculate, antenna impedances the ratio of maximum to minimum directive gain in the plane of the ring, and the mean directive gain in the plane of the ring.