Study On Broadband Polarization Converter Based On Metamaterials

Electromagnetic metamaterial is a kind of artificial structure that is arranged in a specific way by metals and media that are common in nature,and exhibits electromagnetic properties that are not found in natural materials.By changing the structural design or structural size of the electromagnetic metamaterial,the amplitude and phase of the electromagnetic wave can be arbitrarily regulated.Therefore,electromagnetic metamaterials are widely used to design perfect absorber,invisibility cloak,polarization converter,et al.In this paper,by analyzing the regulation mechanism of electromagnetic metamaterials on the amplitude and phase of electromagnetic wave,it is found that theses angle-cutting type absorbers reported in past do not have broadband and high-efficiency absorption characteristics.On the contrary,this type of structure has the potential to realize broadband polarization conversion.On this basis,the structural characteristics of the broadband polarization converters based on metamaterials are summarized,and the broadband polarization converter is designed by optimizing the structure of metamaterial,which realizes the efficient regulation of electromagnetic waves.The main works are listed as following:(1)Through the simulation of the metal patch and the rectangular ring structure,it is found that after the pair of corners of metal patch or the rectangular ring is cut off,the co-polarization reflection coefficient will decrease,but the cross-polarization reflection coefficient will inevitably increase.Based on this,the broadband polarization converter based on anisotropic metamaterial is proposed.The top layer of the structure is double split rings,which are deformed by an absorber based on double square ring structure,it can effectively rotate the polarization direction of incident linear polarization wave by 90?,and the polarization conversion ratio reaches 90% in the frequency range from 6.67 to 17.1 GHz,and the relative bandwidth reaches 87.7%.The sample of the proposed structure have been processed and tested,the results are in good agreement with the simulation results,which verified the correctness of the design.This work provides a new method for designing broadband polarization converters and clarifies the fact that the angle-cutting type absorption structure does not have broadband and high efficiency absorption.(2)Two novel ultra-broadband polarization converters were designed and experimentally verified,and their unit structures are H-shaped and square split ring,respectively.For H-shaped structure,the polarization conversion ratio higher than 90% in the frequency range from 7 to 19.5 GHz,and the relative bandwidth is 94%.Compared to other reflective polarization converter with a single layer structure,it has the advantage in operating bandwidth.The structure also has the property of being insensitive to the incident angle of electromagnetic wave,and even if the incident angle reaches 41.5?,the mean polarization conversion ratio still above 80%.For the square split ring structure,the polarization conversion ratio is higher than 90% in the frequency range from 7.12 to 18.82 GHz,and the relative bandwidth is 90%.The structure also has good performance under oblique incidence of electromagnetic wave,and even if the incident angle reaches 45°,the mean polarization conversion ratio remains above 80%.