Design of superdirective arrays with high radiation efficiency

Superdirective arrays have been considered unrealizable due to the high elemental currents required and their sensitivity to small variations in amplitude and phase. A new approach to superdirective array design based on polynomials which optimize radiation efficiency has been devised. An example of the optimization procedure is given for a 2-wavelength 11-element array, and the sensitivities of radiation patterns optimized for directivity and for radiation efficiency are compared. The relationship between radiation efficiency and the number of elements within a given array length is investigated, and an optimum number is proposed. Finally, the variation of radiation efficiency with beamwidth reduction of optimally filled arrays of different lengths is given.