A modified mills cross with elements spaced one wavelength apart

Abstract

The Mills Cross uses two orthogonal linear receiving arrays whose voltage patterns are multiplied to form a product pattern. With isotropic elements, the element spacing of each linear array is one half wavelength. This paper introduces a modified Mills Cross with isotropic elements spaced one wavelength apart, thereby reducing the mutual coupling between array elements. Moreover, it requires approximately one quarter fewer elements than the original Mills Cross. It uses an x-axis array with elements spaced λ apart beginning at x = λ/2 on the positive x-axis and beginning at x = 0 for elements on the negative x-axis. Two subarrays replace the original linear array on the y-axis of the Mills Cross. They are located one half wavelength on either side of the y-axis. For x = λ/2 the subarray elements are at y/λ = ±1/2, ±3/2, ±5/2, ... and for x = -λ/2 the second subarray elements are at y/λ = 0, ±1, ±2,.... Two product patterns are formed using the x-axis array and the two subarrays in the y-direction. Their sum pattern is the system's output product pattern. It is shown that this pattern can be made equal to the power pattern of a conventional square planar array but with significantly fewer elements and, of course, significantly reduced mutual impedances between the elements.