On null steering in rectangular planar array using external elements

Two methods of null steering in planar arrays are described. One utilizes four external elements oriented along the symmetrical axes of the array and the other uses two of the actual edge elements of the array together with two external elements placed beyond the other ends of the array. In both methods the choice of the external element positions and the use of conjugated phase shifts are utilized to produce a superimposed interferometer pattern whose peaks coincide, approximately, with all of the peaks or the sidelobes and whose zeros coincide with the nulls of the array pattern. Simple closed form expressions for the amplitudes of the cancellation signals that fed to the external elements are given.