A broadband negative-refractive-index transmission-line (NRI-TL) stacked metamaterial for incident plane waves

A volumetric negative-refractive-index transmission-line (NRI-TL) metamaterial is proposed which is based on stacked "dual" shunt nodes. This structure constitutes a natural extension of the planar NRI-TL metamaterials and maintains the desired features of broad bandwidth and low transmission loss. Unlike their planar counterparts, the proposed volumetric NRI-TL metamaterials can effectively couple incident plane waves from free space. A parametric study is undertaken leading to NRI-TL designs exhibiting a 110% backward bandwidth and a 25% transmission bandwidth, respectively.