Beamforming by left-handed extraordinary transmission metamaterial Bi- and plano-concave lens at millimeter-waves

A deep analysis of bi- and plano-concave lens made of stacked subwavelength hole arrays in terms of focus and angular power distribution is presented. The key difference between these left-handed extraordinary transmission lenses (LHET-lenses) and the classical metallic lenses is based on the fact that contrary to the latter ones, LHET-lenses work in the cut-off region of the circular waveguide formed by consecutive stacked holes. This leads to a negative index of refraction, whereas metallic lenses exhibit a positive but less than one index of refraction.