Radiation and near-field coupling between two collinear open-ended waveguides

An experimental and theoretical study of closely spaced collinear coupled waveguides radiating through a common perfectly conducting ground plane is described. The problem is formulated as a set of simultaneous integral equations and solved approximately by expanding the aperture field in a Fourier series. The special case of a single isolated waveguide is treated first, and the results are compared with experiment as well as with the approximate results of Lewin. Attention is given to the edge singularities. The more general case of two collinear coupled waveguide slots is solved by the same numerical method using the symmetrical properties of the geometry. Phase and amplitude of the mutual coupling are evaluated and compared with experiment. Agreement is excellent.