Multilayer negative-refractive-index transmission-line (NRI-TL) metamaterial free-space lens at X-band

A volumetric free-space negative-refractive-index (NRI) transmission-line (TL) metamaterial lens is described that employs fully printed interifigitated capacitors and meandered inductors designed to exhibit NRI properties at X-band (8-12 GHz). The volumetric topology is realized in a layer-by-layer fashion without any vias, which facilitates easy and rapid fabrication. The fabricated lens was tested for its transmission and dispersion properties using a free-space X-band measurement system consisting of an Agilent network analyzer, standard gain horn antennas, and Rexolite dielectric lenses fabricated in-house, and showed good correspondence with simulations. The focusing ability of the multilayer NRI-TL lens was also verified using a free-space field probing system based on small shielded-loop antennas affixed to a computer-controlled xyz-translator apparatus. Arguably, these results represent the first experimental evidence of coupling between TL-based metamaterials and sources in free space.