Abstract: Rectangular waveguides adapted for combination as cross-guide couplers are disclosed. Each waveguide includes opposing sidewalls, a coupling wall and flanges extending from the sidewalls. Each flange has a contact surface in parallel with the coupling wall and is positioned relative to the coupling wall so that the contact surface thereof contacts the coupling wall of the waveguide with which it is combined to form the cross-guide coupler. The coupling wall of one of the waveguides in each coupler includes a coupling aperture. The coupling wall of the other waveguide includes an opening sufficiently larger than the coupling aperture to leave a substantial margin therebetween.