Novel antennas based upon extraordinary transmission metamaterial lenses

Novel antennas exhibiting directivity enhancement by using a short focal length plano-concave lens engineered by stacked subwavelength hole arrays in such a way that an effective negative index of refraction is obtained. An additional unexpected property of this design is that it opens the possibility to achieve an index close to zero, n → 0, arisen from σ- and μ-near-zero extreme values. Our original design works with evanescent modes in comparison with the well known classical metallic lenses operating with propagating modes. In our case, this leads to a negative index of refraction, whereas metallic lenses exhibit a positive but less than one index of refraction. It is demonstrated by means of a simple design based on dispersion diagram and ray tracing an easy and correct method for rather accurate results. Also, an optimization of the hole diameter or longitudinal lattice constant to achieve not only n = -1, but also free space matching is possible simultaneously. A power enhancement up to 24 dB with cross-polarization below -30 dB with regards to copolar, when the lens is applied as antenna radiation beamforming has been measured. For the case of index close to zero, n → 0, the power enhancement is 27 dB whereas the cross-polarization remains -17 dB with regards to co-polar. New improvements are under analysis in order to determine if this technology could be competitive with current state of the art of waveguide lenses and Fresnel zone plate lenses.