Abstract: An antenna includes a truncated waveguide capable of supporting propagation of electromagnetic energy having an electric field component. A dielectric plate is located partially within and partially without the waveguide of the truncation, and is oriented parallel to the E field and the longitudinal axis of the waveguide. An upper half of one side of the dielectric plate bears a conductor pattern defining half of a finline. The lower half of the other side of the dielectric plate bears a second conductor pattern defining the other half of a finline. In the region without the waveguide, the finline diverges to form a radiating portion with high gain. In another embodiment, a finline is formed on both sides of the dielectric plate.