Mutual coupling between sectoral horns side by side

The mutual coupling between two sectoral horns side by side is formulated in terms of the rays, modes, and mode caustics excited in each horn. The coupling term is attributed to the multiple interaction between the aperture edges of both horns and is calculated using Keller's geometrical theory of diffraction. It is shown that this asymptotic method leads to an excellent agreement with experiment and is a considerable improvement over more complicated solutions based on the Huygens' principle.