The design, simulation, and measurement of a complete microstrip line-fed dielectrically guided horn antenna are presented. The proposed antenna achieves similarly high gains as compared to traditional air-filled horn antennas, is simpler than a typical array design, and can easily be fabricated using typical two dimensional substrate machining processes. An H-guide, operating in the fundamental mode, slowly tapers into a “gapped” H-guide, or dielectrically guided horn, where a large air gap separates the center dielectric and metallic plates. A wideband Bézier shaped microstrip to H-guide transition feeding structure is fabricated using a low loss Rogers 5880 substrate and integrated with the proposed antenna. The fabricated prototype operates from 8 to 16 GHz with a peak gain of approximately 16 dBi.