Characterization of Broadband Focusing Microwave Metasurfaces at Oblique Incidence

TL;DR

This paper investigates how angular dispersion in broadband microwave metasurfaces affects their focusing ability at oblique angles, revealing that higher order resonances cause off-axis aberrations and efficiency loss.

Contribution

It provides a detailed analysis of the impact of meta-atom angular response and higher order resonances on broadband metasurface focusing performance at oblique incidence.

Findings

Angular dispersion significantly degrades focusing at oblique angles.

Higher order resonances disturb phase and amplitude responses.

Modeling aligns with experimental results, highlighting angular dispersion as key factor.

Abstract

We report the characterization of an achromatic focusing metasurface at oblique incident angles. We show that in addition to the inherent off-axis aberrations that occurs due to the hyperbolic phase profile of the metasurface, the focusing performance is significantly degraded due to the meta-atoms' angular dispersion. To obtain insights into how the angular and spectral bandwidth of meta-atoms relate to the metasurface focusing performance, point-dipole models are used which incorporate different aspect's of the meta-atoms' angular response. It is emphasized that despite the meta-atoms being designed under the assumption that they support a single dipolar resonance, other resonances exist within the meta-atom geometry and become stronger at oblique incidence. These resonances disturb the designed phase and amplitude responses, resulting in lower focusing efficiency at higher incident angles. The modelling of higher order modes leads to good agreement with the experimental measurements, confirming that angular dispersion of the meta-atoms is the dominant mechanism in determining off-axis aberrations.