Metasurface Design Examples
To demonstrate the aforementioned modeling and optimization procedure, two canonical metasurface designs were created: a soft surface and a hard surface. For simplicity, both designs were optimized for a center frequency of 10 GHz, and neither design included a conductive via from the pattern to the ground plane beneath. Figure 2.3 shows the geometry and simulated responses for the soft and hard metasurface design examples.
Figure 2.3 Pixilated soft (left) and hard (right) metasurface geometry (top), surface reactances (middle), and reflection phase (bottom).
Note that, consistent with the definitions in Eqs. (1.3) and (1.4), the soft metasurface exhibits a surface reactance XTE that is essentially equal to zero, while XTM has a magnitude much greater than zero at the center frequency, and it remains sufficiently below zero for many soft-surface applications across the band. In contrast, the hard metasurface has XTM close to zero across the band, while XTE shows the larger magnitude. An alternative way to interpret soft- and hard-surface operation is to consider the reflection phases of the metasurfaces in the bottom of Fig. 2.3. For the soft case, the metasurface acts as a perfect electric conductor (PEC) for TE-polarized incident waves, while it acts as an AMC for the TM polarization. Meanwhile, the hard design approximates a PEC for the TM-polarized case, and TE-polarized waves see an AMC near the center frequency. This anisotropic reflection behavior gives rise to the anisotropic surface reactances associated with the soft and hard surfaces.