Ultrabroadband diode-like asymmetric transmission and high-efficiency cross-polarization conversion based on composite chiral metamaterial

In this paper, a three layer composite chiral metamaterial (CCMM) is proposed to achieve diode-like asymmetric transmission and high-efficiency cross-polarization conversion by 90° polarization rotation with ultrabroadband range in microwave region, which was verified by simulation and experiment. This CCMM is composed of a disk-split-ring (DSR) structure sandwiched between two twisted sub-wavelength metal grating structures. The simulation agrees well with experiment in principle. The simulation results indicate that the incident y(x)-polarized wave propagation along the −z(+z) direction through the CCMM slab is still linearly polarized wave with high purity, but the polarization direction is rotated by ±90°, and the polarization conversion ratio (PCR) is greater than 90% in the frequency range of 4.36–14.91 GHz. In addition, in the above frequency range, the asymmetric transmission coefficient (Δ_lin) and the total transmittance (T_x) for x-polarized wave propagation along the −z axis direction are both over 0.8. Finally, the above experiment and simulation results were further verified by the electric field distribution characteristics of the CCMM unit-cell structure. Our design will provide an important reference for the practical applications of the CCMM for polarization manipulation.