Element Efficiency: A Unifying Concept for Array Antennas

The antenna-element efficiency parameter quantifies the effect of mutual coupling in array antennas. In general arrays, this efficiency varies from element to element. The average value of these element efficiencies is a significant summary parameter, and plays a prominent role in circumscribing array performance. A useful formula gives the minimum number of antennas necessary to realize a prescribed peak gain envelope. The important special case of an array of identical elements situated in identical array environments is termed an idempotent array. In particular, an infinite idempotent array models a large planar array. There, the unique element efficiency has been directly related to the rms value of the conventional active reflection coefficient as it varies when the beam is (phased) electronically steered. The element-efficiency formulation also provides a framework for the rigorous derivation of important theoretical results in the theory of phased arrays.