Enhanced Gain by Double-Periodic Stacked Subwavelength Hole Array

Using a doubly periodicity structure the extraordinary transmission of subwavelength metallic hole arrays in the microwave range can be boosted. Stacking several of such plates a left-handed metamaterial can be obtained as it is shown by the computed dispersion diagrams as well as the amplitude and phase measurements. An effective refraction index along the propagation direction can be calculated, giving a negative magnitude between ${-}$1 and 0. This enhances the emission by a focused beam with narrow beamwidth. Several practical applications like novel antennas are envisaged.