Miniaturization of 3-D Anistropic Zero-Refractive-Index Metamaterials With Application to Directive Emissions

Several strategies are explored for the first time toward the miniaturization of three-dimensional (3-D) anistropic zero-refractive-index metamaterials (AZIM). By incorporating the fractal, spiral, and meandered resonant metallic inclusions within a host dielectric medium, several AZIM elements are engineered in subwavelength at the plasma frequency. The influences of geometrical shape, arrangement, and dimensions of inclusions on electromagnetic features of the 3-D elements are also investigated to obtain the design guideline. In this frame, we have designed a set of AZIM elements with near-zero permittivity and near-zero permeability occurring at the same frequency. To demonstrate potential applications, a lens horn antenna by loading the 3-D AZIM lens has been designed, fabricated, and measured. Numerical and experimental results agree well and illustrate that the beamwidth of the E-plane pattern has reduced about 4.9^° while that of the H plane has reduced about 6.7^°. Moreover, the gain of the lens horn antenna has improved 1.6 dB relative to its conventional counterpart with identical aperture. The proposed avenue in 3-D AZIM design advances a step toward the compactness and homogenization.