# Accurate metasurface synthesis incorporating near-field coupling effects

## TL;DR

This paper introduces an extended equivalent-circuit model for metasurface synthesis that accurately accounts for near-field coupling effects, improving design precision especially at higher frequencies.

## Contribution

The authors develop a novel extension of the impedance sheet model to include near-field coupling, enabling more accurate metasurface synthesis.

## Key findings

- Extended model predicts scattering parameters accurately
- Synthesized metasurface achieves near-theoretical efficiency
- Improved design algorithm compensates for near-field perturbations

## Abstract

One of the most promising metasurface architectures for the microwave and terahertz frequency ranges consists of three patterned metallic layers separated by dielectrics. Such metasurfaces are well suited to planar fabrication techniques and their synthesis is facilitated by modelling them as impedance sheets separated by transmission lines. We show that this model can be significantly inaccurate in some cases, due to near-field coupling between metallic layers. This problem is particularly severe for higher frequency designs, where fabrication tolerances prevent the patterns from being highly-subwavelength in size. Since the near-field coupling is difficult to describe analytically, correcting for it in a design typically requires numerical optimization. We propose an extension of the widely used equivalent-circuit model to incorporate near-field coupling and show that the extended model can predict the scattering parameters of a metasurface accurately. Based on our extended model, we introduce an improved metasurface synthesis algorithm that gives physical insight to the problem and efficiently compensates for the perturbations induced by near-field coupling. Using the proposed algorithm, a Huygens metasurface for beam refraction is synthesized showing a performance close to the theoretical efficiency limit despite the presence of strong near-field coupling.