Dielectric prisms are widely utilized in the design of the millimeter wave and optical functional components, which are used in communication systems [1, 2]. Dielectric prisms coupled to open dielectric waveguides can also be used as versatile leaky-wave antennas due to their ability to convert a waveguide surface wave to a beam [2]. Among their advantages are low weight, low losses, simple coupling technique and high radiation efficiency. For any given prism configuration and wavelength, the radiation angle of a beam varies with the surface mode number. If a waveguide supports several higher-order modes, the output far-field radiation pattern has several well-defined beams corresponding to these modes.