Coupling of waveguides through large apertures

A closed-form expression for the equivalent network parameter of a transverse slot in the common broadwall of two coupled rectangular waveguides is derived in terms of self-reaction (Harrington, 1961) and modal-voltage discontinuity (Marcuvitz and Schwinger, 1951). A comparison is drawn between the computed results with those obtained by Marcuvitz (1951) for a full-length slot and by Levinson and Fredberg (1966) for slot length greater than the broad dimension of the waveguide, as well as with the coupling calculated from Sangster's (1965) formula and with experimental results. The analysis presented is quite general and can be used to evaluate the equivalent network and hence the coupling for apertures in the common wall of any two arbitrary waveguides.