Leaky-wave propagation and radiation for a narrow-beam multiple-layer dielectric structure

Previous work has demonstrated that very narrow beam radiation patterns can be obtained from a simple source embedded within multiple dielectric layers of appropriate thicknesses above a ground plane. The configuration consists of dielectric layers having permittivities ε₁ and ε₂ stacked in an alternating arrangement, with ε₂>ε₁. This narrow-beam effect can be attributed to weakly attenuated leaky waves that exist on the structure. Simple asymptotic formulas for the propagation and attenuation constants are derived. The formulas show how the beamwidth varies with the number of layers and the material constants. The exact radiation pattern is compared with the leaky-wave pattern for a specific case to demonstrate the role of the leaky waves in determining the total pattern