The Fundamental Physics of Directive Beaming at Broadside and the Role of Leaky Waves

The fundamental mechanism behind directive beaming at broadside for various structures will be explored. These include Fabry-Pérot type of resonant-cavity antennas, low-permittivity metamaterial substrate antennas composed of a wire medium slab, and optical directive beaming due to plasmonic effects. In all cases it will be shown that the fundamental explanation for the directive beaming effect is the excitation of one or more leaky waves. Leaky-wave theory predicts a simple condition for maximum directive beaming at broadside, namely that the phase and attenuation constants of the leaky wave(s) are equal.