Crossed waveguide directional couplers for high power applications

The small aperture coupling theory of the broad wall to broad wall (Moreno) coupler is reviewed and extended. It is shown that a lower limit on the directivity is given by the ratio of magnetic polarizability to electric polarizability for the coupling apertures. Hence directivity may be improved by using very narrow crossed slots for coupling. The results of coupling measurements on a Moreno coupler are presented to demonstrate the accuracy of the small aperture theory. A small aperture design procedure has also been developed for the narrow wall to broad wall coupler, which takes into account the effect of wall proximity on slot coupling. The measured results for the manufactured coupler are in excellent agreement with this theory.