A new leaky-wave antenna (LWA) for continuous beam scanning and broadside radiation is presented. The fabricated and measured planar antenna is fed by surface waves (SWs) and defined by a periodic arrangement of width-modulated microstrip lines for leaky wave ( LW) excitation and radiation. In addition, a novel transition section near the SW source controls the leakage rate as well as the aperture distribution. Results are further supported by theoretically determined dispersion diagrams (DDs) in terms of Mathieu functions. Far-field beam scanning is also observed over a large radiating bandwidth (19.0 GHz to 26.3 GHz) for the measured and simulated LWA with pointing angles ranging from -26 degrees to +35.0 degrees in the E(x-z) plane.