Superdirective end-fire array

Abstract

A ten-element end-fire line array was designed for use as a superdirective array. A superdirective array can produce a sharper beamwidth by accepting a reduced sensitivity on the main beam. This is potentially very advantageous since a reduction of only a few decibels in sensitivity can reduce the beamwidth by as much as one-third. A design curve is presented for the superdirective ten-element array which relates the required phase shift between the elements to beamwidth and relative peak sensitivity as a function of frequency and element wavelength spacing. Also presented on these curves is the change in beamwidth with frequency when the requisite phase shift is produced by an ideal delay line. Directivity patterns are given which exhibit a −3 dB beamwidth reduction from 70° to 41° with a sensitivity loss of 7 dB. The experimental results agree reasonably well with theoretical predictions. [Work supported by NAVSEA.]