Introduction of a sharp steerable null response in an otherwise omni-directional pattern using a circular array

A technique generating a sharp zero-crossing null response in a particular direction while the radiation pattern away from the null is kept essentially constant is discussed. The null is electronically steerable over 360 deg (including in the elevation plane), thanks to a Butler matrix, so that null steering can be handled in the manner of beam steering in a linear array of equal inter-element spacings. The resulting directional patterns exhibit useful null width and gain ripple characteristics. Mutual couplings between elements are without effect on the pattern function, since all array elements experience identical coupling environments, with all components of excitations in the array featuring an integral number of cyclic phase variations around the array.