A transition device for transitioning microwaves from an air-filled waveguide to an antenna. The air-filled waveguide is assumed to have an attachment flange, with the transition device having a compatible transition attachment flange. A rod has an upper portion extending upwardly through the flanges and a lower portion extending downwardly into the air-filled waveguide. The rode is made from a solid piece of high-dielectric material. The rod's outer surfaces of the upper portion (other than its end face) are metal plated, such that the upper portion provides a solid waveguide having a radiating aperture antenna.