Bianisotropic Metasurface for Spatial Separation of Multiple Harmonic Waves

An approach to tuning harmonic responses of surface impedance is introduced to spatially separate fundamental, third-harmonic, and fifth-harmonic waves by focusing on the physical implementation perspective. The concept of the bianisotropic metasurface is adopted to refract the wave toward different angles by assigning identical phase gradients at fundamental and third-harmonic frequencies. On the other hand, high-sheet impedance is realized by maintaining the in-phase condition at the fifth harmonic to bypass the incident wave without refraction. The target properties of each unit cell are implemented using I-shaped patterns based on a three-stacked-layer topology. Different sizes and intervals are applied for the I-shaped patterns, and only their horizontal lengths are tuned to achieve the desired sheet impedances. The feasibility of the proposed approach is validated for the fundamental frequency of 10 GHz and two of odd harmonics through far- and near-field measurements. The results confirm that the fabricated metasurface separates the superimposed harmonic waves toward 44°, 10°, and 0° with the measured refraction efficiencies of 65.6%, 67.2%, and 74% at 10, 30, and 50 GHz, respectively.