Bandwidth Limit and Synthesis Approach for Single Resonance Ultrathin Metasurfaces

TL;DR

This paper establishes fundamental bandwidth limits for ultrathin metasurfaces based on physical constraints and proposes a synthesis method to significantly enhance their bandwidth, demonstrated through experimental validation at millimeter-wave frequencies.

Contribution

It derives a theoretical bandwidth limit for passive, causal, lossless metasurfaces and introduces a synthesis approach that achieves over 90% bandwidth enhancement.

Findings

Bandwidth limited by substrate thickness and permittivity.

Proposed LC resonance synthesis method improves bandwidth.

Experimental validation shows significant bandwidth increase.

Abstract

Metasurfaces have emerged as a promising technology for the manipulation of electromagnetic waves within a thin layer. In planar ultrathin metasurfaces, there exist rigorous narrowband design methods, based on the equivalent surface impedance of patterned metallic layers on dielectric substrates. In this work, we derive a limit on bandwidth achievable in these metasurfaces, based on constraints that their meta-atoms should be passive, causal and lossless, and that they should obey the time-bandwidth product rules of a single resonance structure. The results show that in addition to elementary design parameters involving variation of the surface impedance, the bandwidth is critically limited by the dielectric substrate thickness and permittivity. We then propose a synthesis method for broadband ultrathin metasurfaces, based on an LC resonance fit of the required surface impedance, and experimentally verify a broadband dispersive structure at millimeter-wave frequencies. This results in a bandwidth enhancement of over 90%, relative to a reference metasurface created with the narrowband design process.