Superdirectivity with Appreciable Bandwidth in Arrays of Radiating Elements FED by Microwave Transistors

The incorporation of transistors into the radiating elements of an array antenna leads to a suppression of the elemental mutual coupling effects in the feed network. Because of this suppressed interaction, it is possible to re-appraise the practical exploitation of Schelkunoff´s principle that an arbitrarily high gain can be obtained from a given array size by suitably feeding the individual elements. A four-element end-fire superdirective array with a total length of 3¿/8 and a theoretical beam width of 60° has been investigated. The computed radiation patterns of the passive array indicate the extreme sensitivity to changes in frequency consistent with the classical limitations of supergain arrays. An experimental active array is described which permits the superdirective performance to be maintained over an appreciable frequency band.