A dual-layer antenna that utilizes bound surface waves for leaky wave excitation is presented for microwave and millimeter-wave applications. Specifically, by placing a superstrate dielectric layer and ground plane on top of a base grounded dielectric slab a resonant cavity can be realized defining a parallel-plate guiding structure. Antenna leakage can be achieved by an annular 'bull-eye' grating of slots etched in the top ground plane for two-side beam scanning. In addition, a single pencil beam at broadside can be observed over a large radiating bandwidth (21.9 GHz to 23.9 GHz) with measured antenna gain values > 12:6 dBi from 22.3 GHz to 23.7 GHz. Essentially the bidirectional field distribution on the aperture is excited by a non-directive surface-wave launcher (SWL) source embedded in the bottom ground plane. This dual-layer structure and printed SWL feed may be useful for new parallel-plate wave guide configurations and other planar leaky-wave antennas.