Randomly spaced phased arrays with large interelement spacings

Phased arrays with interelement spacings greater than one half wavelength result in grating lobes whose amplitudes approach that of the amplitude of the main beam. These grating lobes can be reduced by making the interelement spacing aperiodic. Grating lobe reduction has been accomplished by deterministic aperiodic spacing, e.g., logarithmic spacing; by thinning, i.e., randomly removing elements from an array in which elements are spaced one-half wavelength apart; and by locating elements in a random manner. The random arrays that have been treated (Ref. 1-4) have had probability density functions of the element positions which would require a significant fraction of the elements to be spaced less than one half wavelength apart. These analyses, therefore, appear to be restricted to arrays whose elements are less than one half wavelength in size. In the millimeter and shorter wavelength regions where the typical antenna may be a dish or horn, spacings of one half wavelength or less are often precluded from consideration so that the previous analyses are inapplicable.