Characterization of negative refraction with multilayered mushroom-type metamaterials at microwaves

In this paper, it is shown that bulk metamaterials formed by multilayered mushroom-type structures enable broadband negative refraction. The metamaterial configurations are modeled using homogenization methods developed for a uniaxial wire medium loaded with periodic metallic elements (for example, patch arrays). It is shown that the phase of the transmission coefficient decreases with the increasing incidence angle, resulting in the negative spatial shift of the transmitted wave. The homogenization model results are obtained with the uniform plane-wave incidence, and the full-wave results are generated with a Gaussian beam excitation, showing a strong negative refraction in a significant frequency band. Having in mind a possible experimental verification of our findings, we investigate the effect of introducing air gaps in between the metamaterial layers, showing that even in such simple configuration the negative refraction phenomenon is quite robust.