Polarization Considerations for Scalar Huygens Metasurfaces and Characterization for 2-D Refraction

Transmitarrays and transmissive metasurfaces must efficiently couple incident power to the transmitted beam. Inefficiency is manifested in sidelobe levels, reflections, and insertion loss. The Huygens metasurface embodies the Huygens and equivalence principles, suppressing these sidelobe levels and reflections. This is accomplished with a single thin layer of Huygens sources, which contains both an electric and a magnetic response. In this paper, 2-D interfacial refraction is implemented with a scalar Huygens metasurface. The measured total efficiency is on average 71.06% for a 70° range, the maximum being 80.87% at θ_i=0°. Moreover, it is on average 68.64% over a fractional bandwidth of 8%, the maximum being 80.87% at 10.0 GHz. This demonstrates that the insertion loss, reflection, and sidelobe powers are low in our design. Furthermore, the questions of polarization purity, and the appropriate polarization definition for a scalar Huygens metasurface, are addressed. Our design contains only printed elements, and consists of two bonded boards, instead of many stacked interspaced layers. This simplifies fabrication, and makes it scalable to millimeter-wave frequencies and beyond. The design is also λ/9.3 thick, in contrast to traditional transmitarrays, which require 3-4 λ/4 spaced layers to obtain the same degree of phase control and matching.