Application of modal analysis to a waveguide-cavity junction formed by an iris obstacle

This paper describes an application of the modal-analysis technique for studying the coupling of a circular waveguide to a cylindrical cavity via an infinitely thin iris obstacle containing a central circular aperture. It confirms that, for this type of coupling problem, for optimal convergence the equality of the ratios m : q : n and RA : ra : RB needs to be taken, where m, q and n are, respectively, the number of waveguide modes, aperture functions and cavity modes, and RA, ra and RB are the corresponding radial dimensions. The results obtained are compared with those derived from a transmission-line model and experiment.