Signal/noise performance of super-directive arrays

A super-directive array is defined as one whose effective aperture exceeds its physical aperture, and it is shown that while such an array has a Directivity Index somewhat better than that of an ordinary array, nevertheless its Noise Factor is much worse. Consequently, in many receiving systems, the use of super-directivity is not be recommended. The conception of super-directivity is extended to bearing-determining arrays which give a null response on the axis, and it is shown that the same disadvantage of a bad Noise Factor applies to them also.