Controlling Electromagnetic Surface Waves with Scalar and Tensor Impedance Surfaces.

Abstract

The propagation characteristics of electromagnetic waves on various isotropic (scalar) impedance surfaces have been studied for some time, in order to control surface waves and leaky-wave radiation. One and two dimensional periodic impedance surfaces as well as tensor impedance surfaces, have been explored for enhanced control of wave guidance. The desire to integrate antennas and electromagnetic devices onto the surfaces of vehicles and other platforms has driven recent interest in both scalar and tensor impedance surfaces. Great strides have been made in the design of devices based on impedance surfaces. To date, these devices are designed by first determining the surface impedance variation necessary to yield the desired performance. The surfaces are then implemented as printed-circuit board (PCB) structures consisting of a patterned metallic cladding over a grounded dielectric substrate. In other words, these two-layer structures are modeled with an idealized tensor impedance boundary condition.

In this work, we aim to capture the propagation characteristics of PCB-based tensor impedance surfaces more accurately by modeling them as an impedance sheet over a grounded dielectric substrate. The impedance sheet represents the patterned metallic cladding of the PCB tensor impedance surface. Dispersion equations for scalar and tensor PCB versions are found. In addition, an extraction method is presented that allows the impedance sheet to be found using only two full-wave simulations. Using the dispersion equation and the extraction method together, the dispersion properties of the printed-circuit impedance surface can be predicted. A method for designing transformation electromagnetics devices using tensor impedance surfaces is also presented. Further, a printed leaky-wave antenna based on a sinusoidally modulated scalar impedance surface is presented.