Equivalence of Polarizability and Circuit Models for Waveguide-Fed Metamaterial Elements

TL;DR

This paper demonstrates the equivalence between polarizability models and circuit models for waveguide-fed metamaterial elements, enabling more efficient and insightful design of large metasurface antennas with integrated circuits.

Contribution

It establishes a formal equivalence between polarizability and circuit models for metamaterial elements, facilitating advanced metasurface design and integration of complex external circuits.

Findings

Derived circuit models for basic metamaterial elements

Confirmed models using full-wave simulation scattering parameters

Enabled integration of lumped elements and active devices into metamaterial models

Abstract

A common variant of a metasurface antenna consists of an array of metamaterial elements coupled to a waveguide feed. The guided wave excites the metamaterial elements, coupling energy from the waveguide mode to radiation. Under appropriate conditions, each sub-wavelength metamaterial element can be modeled as a polarizable dipole, with the polarizability determined by an extraction procedure from the computed or measured waveguide scattering parameters. Here we establish the equivalence of this polarizability description of a metamaterial element with an equivalent circuit model, providing an additional tool for metasurface design that offers significant insight and a path towards efficiently modeling very large apertures. With this equivalence established, more complicated external circuits that include lumped elements and devices such as diodes and transistors can be integrated into the metamaterial element, which can then be transformed into an equivalent polarizability for modeling in the coupled dipole framework. We derive appropriate circuit models for several basic metamaterial elements, which provide direct relationships between the equivalent circuit parameters of an element and its effective polarizability. These expressions are confirmed using scattering parameters for several example structures obtained via full-wave simulations.