The equivalent circuit of a rectangular-waveguide-fed longitudinal slot

Long-standing practice has been to view a longitudinal slot in a broad wall of a rectangular waveguide as a shunt element. This becomes a more questionable assumption as the b dimension of the guide is decreased and/or the slot offset is increased. A symmetrical T or\pimodel of the slot is more accurate. A procedure for developing the parameter values of the T or\piis described. The further complication of accounting for external mutual coupling is also discussed.