Mutual coupling in a finite planar array of rectangular apertures

A technique for calculating the mutual coupling within a finite planar array of rectangular apertures is developed, using waveguide modes to describe the aperture fields. Expressions for the coupling between the various modes can be derived, and, as an example case, the TE-to-TE coupling in coincident apertures is chosen to both illustrate the derivation and show how the expressions could be evaluated numerically.