Mutual coupling between rotated horns in a ground plane

Two formulations are presented for the mutual admittance of rotated rectangular apertures in a ground plane. One extends an earlier solution, and the other is a third-order asymptotic formula that is shown to be accurate when the apertures satisfy the Rayleigh distance criterion. These formulations are combined with a conventional mode-matching approach to study coupling between rotated horns. Results are presented for both coupling formulations, and these demonstrate excellent agreement with experiment for coplanar pyramidal and sectoral horns