A radar assembly includes a rectangular-waveguide (RWG) and a printed-circuit-board. The rectangular-waveguide (RWG) propagates electromagnetic energy in a transverse electric mode (TE10) and in a first direction. The printed-circuit-board includes a plurality of conductor-layers oriented parallel to each other. The printed-circuit-board defines a substrate-integrated-waveguide (SIW) that propagates the electromagnetic energy in a transverse electric mode (TE10) and in a second direction perpendicular to the first direction, and defines a transition that propagates the electromagnetic energy between the rectangular-wave-guide and the substrate-integrated-waveguide. The transition includes apertures defined by at least three of the plurality of conductor-layers.