Design Of Reflective Mode Polarization Converter Based On Anisotropic Metamaterials

A new type of functional material composed of subwavelengths of periodic structures-metamaterials,has many singular properties that are not possessed by natural materials,such as negative refraction phenomena,super-resolution imaging,electromagnetic stealth,high impedance surfaces,and extremely strong electromagnetic polarization rotation ability and so on.Polarization is one of the important characteristics of electromagnetic waves,widely used in wireless communications,liquid crystal display,optical data storage and other fields.Polarization converters based on metamaterials have the advantages of thin thickness,large bandwidth and high efficiency,and have become an important way for people to control the polarization state of electromagnetic waves efficiently.In this paper,a reflective polarization conversion converter based on ladder-shaped metamaterials element is designed,which realizes the linear polarization conversion with high conversion efficiency.The converter can convert incident linearly polarized electromagnetic waves into cross-polarized reflected waves in the frequency range of 6.9 ~ 5.4GHz,the conversion efficiency is higher than 0.9.The converter has a large incidence angle and a high polarization selectivity,be able to maintain high conversion efficiency when the incident angle increases from 0 to 30 ° and can only perform 90 ° polarization conversion on x-polarized or y-polarized incident waves.The incident electromagnetic wave and the polarization converter undergo a magnetic,magnetic,electric harmonic resonance response in three frequencies of 7.4GHz,11.5GHz and 14.8GHz respectively,resulting in a large working bandwidth.The Fabry-Perot multiple interference theory shows that the destructive interference of multiple co-polarized reflected waves is the reason why the converter has high conversion efficiency.The results of polarization conversion efficiency of experiments,theoretical calculations and simulations are very consistent with each other.Next,a dual-mode reflective polarization converter is proposed in which the resonant structural element consists of a small solid circle and a large ring,and the solid circle and the ring are connected by two thin metal wires in the direction of 45 °.The polarization converter can convert the incident linearly polarized wave into a cross-polarized reflected wave in the frequency range of 7.95 ~ 9.93 GHz,and convert into a left-handed circularly polarized reflected wave in the frequency range of 10.14 ~ 11.56 GHz,both the cross polarization and circular polarization conversion efficiency are greater than 0.9.The dual polarization conversion mode is highly sensitive to the geometric dimension.The converter has a good dual-polarization conversion mode only when the radius of the solid circle r = 5mm,the radius of the ring R = 8mm,and the dielectric layer thickness d = 10 mm.The equivalent impedance Z calculated by the equivalent media theory maintains a high degree of consistency with the phase ? change of the reflection coefficient,indicating that the anisotropy of the impedance results in the reflection phase difference in the different polarization directions is the source of polarization conversion capability of the converter.