Abstract
A novel metasurface comprised of capped helices arranged as a hexagonal array that supports a broadband near-isotropic negative-index microwave surface-wave is designed, manufactured, and experimentally characterized. The surface-mode dispersion is studied both numerically and experimentally with the operational band more than double the bandwidth of structures previously reported in the literature. Hence, it is shown how one may provide a structured surface that supports just a negative-index mode over a wide operational band with no forward wave being simultaneously excited.
Highlights
Since the start of metamaterials research, possibly the most known effect that has been observed in metamaterial structures is that of negative refractive index
For many practical applications it may be useful to have structures with a more isotropic response. To address this issue we propose using an hexagonal array instead of a square one
There are several ways to increase the coupling values and broaden the bandwidth of the negative dispersion region even further. (Higher order modes in this case have much the same overall dispersion structure as for the square array.) Here and further on we will calculate the operational band of the hexagonal structures based upon the lowest and highest frequencies in the y direction
Summary
Since the start of metamaterials research, possibly the most known effect that has been observed in metamaterial structures is that of negative refractive index. Using the coupling retrieval method discussed in [23], it can be demonstrated that helical elements in a planar arrangement have both negative magnetic and electric coupling between them. This results in negative dispersion as demonstrated in [10]. In this work we explore structures of such capped helices that combine negative magnetic and electric couplings As a result, this strongly subwavelength structure provides an extremely broad negative-index mode that provides, to the best of our knowledge, a significantly wider percentage bandwidth at low GHZ frequency range than those presented in the literature.
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