Extraordinary Transmission by Double-Sided Hyperbolic Metasurfaces With $\Gamma$ -Point Degeneration at Millimeter-Wave Bands

We propose a hyperbolic metasurface with the Γ-point degeneration for demonstrating the extraordinary transmission with the transmittance exceeding unity at millimeter-wave bands. The enhanced transmittance is realized by a beam narrowing of the transmitted wave through the metasurface that works as an effectively enlarged aperture with the in-phase excitation of the guided modes at the Γ-point. In order to efficiently accelerate the guided modes of the metasurface at the Γ-point by the incident wave and to avoid the energy leakage to cross-polarized waves, we introduce the Γ-point degeneration and hyperbolic anisotropy in the metasurface. First, we theoretically investigate the dispersion characteristics and hyperbolic nature of the proposed structure based on the equivalent circuit model, and we design the unit cell of the metasurface to realize the Γ-point degeneration at 34 GHz by full-wave simulations. Then, we demonstrate the extraordinary transmission both numerically and experimentally. Our experiments reveal that the transmittance with the metasurface exceeds that without the metasurface by 5 dB at the Γ-point frequency of 34 GHz.