Wide-band Asymmetric Transmission for Linearly Polarized Wave Using Bi-layered Chiral Metamaterial

In this paper, a metal-dielectric-metal configuration is employed. The unit cell of the proposed chiral metamaterial design consists of a simple 'EI' shape resonator printed on two opposite sides of dielectric substrate. The metal pattern on the front and back layers is identical, with the exception that the back-layer pattern twisted at a 90o angle to break mirror symmetry in the propagation direction. The optimized dimensions (in mm) of the unit cell are: w=1.5, w1=1.5, d=1, b=6, m=3, h=1.6 and a=8. The dielectric substrate is Roger 5080, which has a dielectric constant εr = 2.33, and tangent loss tan δ = 0.0005. The copper sheet is used as a metallic pattern having a thickness of 35um, and an electrical conductivity of 5.8 x 107 S/m. Commercially available software called CST Microwave Studio is used to carry out the numerical simulations of the suggested design. Unit-cell boundary conditions were applied in the y- and x-directions, while open boundary conditions were used in the z-direction. The numerical simulation is carried out in the frequency range of 11 GHz to 23 GHz. Through numerical simulation, complex transmission coefficients are produced, from which the asymmetric transmission, total transmission and polarization conversion ratio are calculated. The simulation results of complex transmission coefficients for linearly polarized waves in the forward (+z) and backward (-z) direction of propagation shows wide, strong peaks.