Dual-Polarized Volumetric Transmission-Line Metamaterials

Most metamaterial unit cells are designed for a single polarization only. Those that do work for multiple polarizations are often difficult to fabricate as they require a three-dimensional arrangement of circuit boards. To get around this trade-off a new volumetric transmission-line metamaterial unit cell is introduced which supports two polarizations. The two-dimensional transmission-line network found in the unit cell contains both series-node and shunt-node grids, making it the first unit cell to combine these two configurations. This allows the unit cell to be fabricated by simply stacking printed circuit boards. This series-node/shunt-node configuration allows the unit cell to support two polarizations and makes the unit cell isotropic and polarization independent for cylindrical waves. Another unique feature of this proposed unit cell is that it achieves dual-polarized behaviour without using symmetry. To verify this concept an example unit cell is designed, exhibiting a negative index of refraction for two polarizations. Full-wave dispersion analysis is used to verify the presence of overlapping backward-wave modes at the same frequency range. Then the S-parameters for a finite number of unit cells are analyzed to determine the effective index of refraction. Multi-conductor transmission-line theory (MTL) is also used to model the dispersion curves of the unit cell for both polarizations. Finally, using full-wave simulations, dual-polarized negative refraction is demonstrated using a slab that is five unit-cells thick.