The left-handed (LH) operation of a three-dimensional (3-D) LH material composed of wired metallic spheres is experimentally confirmed. A 15153-cell periodic structure designed to have an isotropic LH characteristics is fabricated by a 3-D printer with post plating technology, and near-field measurements of refracted waves by the negative refractive index slab lens are carried out. The dispersion characteristics measured from the near-field distributions on the surface of the LH material clearly show that the structure supports the backward waves at 12 GHz band. It is also shown experimentally that the resolution of the slab lens exceeds the diffraction limit by near field measurements with a single source and adjacent two sources. In addition, near-field measurements from the LH material near the Γ-point frequency at 12.90 GHz are carried out. A highly directive plane wave with a single point source is observed and the near-zero-index operation has been confirmed.

A novel purely distributed two-dimensional (2D) planar structure with a negative refractive index (NRI) is proposed. The structure consists of a 2D periodic array of unit cells with metal patterns on the both sides of a substrate. The unit cell with the dimension of 55 mm2 is designed at an operation frequency of about 5 GHz by full-wave finite element method simulations. Numerical simulations on the dispersion characteristics are carried out and NRI property of the structure is confirmed. A equivalent circuit taking into account the mutual capacitance between the adjacent ports in the unit cell is introduced, and theoretical investigations based on the equivalent circuit reveals that the anisotropy can be controlled by the mutual capacitance. A 1020 unit-cell NRI material is fabricated and the NRI property has been confirmed experimentally in excellent agreement with Snell's law.