Wideband equivalent circuit of a centered-inclined waveguide slot coupler

A centered-inclined waveguide slot coupler has been modeled as a series-ser ies ideal transformer since ever. Actually this equivalent circuit is not e xact, but only approximate though, for resonant couplers, the approximation being usually very good. The approximation gets worse as the slot length m oves away from resonance, and is completely useless for off-resonant slots, needed in shaped-beam slot arrays. In this paper, an in-depth discussion o f the properties of such a slot coupler and of the admissible approximation s allows to quantitatively set the limit of the "standard" model, and leads to suitable generalizations to non-resonant slots as well. The resulting e quivalent circuits are compared against full-wave simulated data and result to be very accurate in a quite large frequency range.