| Polarization is the property of electric field intensity,it represents the changing of orientation and amplitude of electric field with time,and is also called rotation in the optical field.In microwave and optical equipment,it is often necessary to obtain specific polarized EM waves.Conventional polarization control devices are achieved by prism rotators based on total internal reflection principle,or the principle of birefringence,or based on optical gratings and dichroic crystals.However,they usually have complex design and large thickness,which is not conducive to miniaturization and integration and also cost much in fabrication processes.And considering the property of these devices,there are also shortcomings such as narrow frequency band,single mode,and poor polarization selectivity and so on.Artificial metamaterials have the performance which the natural materials do not have.The artificial polarized converter can achieve arbitrary control of phase and amplitude of EM waves through different designed units,which is expected to break the limitations of conventional polarized converter.According to present research,for the artificial polarized converter design,the main problems include narrow frequency band,simple mechanism,hard to achieve lowfrequency polarization control,and hard to accomplish multi-polarization conversion.To solve the above problems,this dissertation researches the properties of artificial polarized converters and achieved dual-band,high efficiency,broadband,multi-performance and low-frequency polarization property,and also researches the mechanism deeply.In addition,combining the artificial polarization conversion design with the scattering control,it has proposed a design and research of scattering control.The main research contents and innovations of this dissertation are as follows:(1)The mechanism of the artificial polarization design is researched deeply.Aiming at the current problem in research of polarization mechanism,the transmission matrix theory,equivalent impedance theory and equivalent circuit theory have been combined to solve these problems.The relationship of the polarization bandwidth,the resonance frequency point and the size parameters of the converter has been established,and the analysis theory applicable to the polarized converter is constructed.The polarized bandwidth is expanded,and the EM resonance mechanism is used to solve the problem of achieving low-frequency design,which is based on the phase and amplitude property of the transmitting or reflecting EM wave.This way will give the instructions to the design of broadband,low frequency and multi-band polarized converter.(2)Different properties of polarized converters are proposed.For the current situation that the frequency range is narrow and it is difficult to achieve low-frequency polarization control.To solve these problems,the reflected polarized converters which have the properties of dual-band,broadband,low resonance frequency and high conversion efficiency have been researched,respectively.And the influence of the oblique incidence angle and the parameter of the dielectric thickness also have been analyzed.By used of the symmetry and antisymmetric theory,the resonance mechanism of the polarization control is clarified,and the dual-band polarization property are realized by the bound modes of Fano resonance in the converter.The existence of the modes enables the converter have stable dual-band property at a large incident angle,and provides a new way to the design the dual-band converter.Based on the transfer matrix theory and the equivalent surface impedance theory,the relationship between the equivalent impedance and the reflection coefficient of the converter is established.Through simulation and theoretical calculations,the resonance and high-efficiency broadband properties are analyzed,and the physics mechanism of multi-order resonance is researched deeply.This provides the theoretical guidance for the research of broadband performance.Aiming at the current dilemma that the polarization converter is difficult to achieve at low frequencies,combined the equivalent circuit theory and EM resonance mechanism,innovative researched and designed the low-frequency polarized converter based on the Non-Foster circuit design.The resonance frequency and the size parameters of the converter has been constructed.This method put the foundation for low-frequency design.(3)Based on the design of defect perfect electrical conductor(PEC),an artificial polarized converter which can realize reflection and transmission properties is proposed,and the control of multi-functional polarization based on the defect is researched.The property of the low frequency band and high frequency band is realized differently by adjusting of the defect size factor.The effect of the oblique incidence angle on the converter is also be analyzed,and the property of the reflection and transmission crosspolarization of this converter is stable within a range of 50°.The polarization filtering function can be realized by adjusting the parameters of the double-layer defect PEC of the converter.The broadband and selective property can be realized through the multicoupling between the converter.The proposed converter can be used to design the polarization selection filter.(4)Based on the artificial polarized converter,the research of scattering property of reflectarray is carried out.A checkerboard structure is designed firstly to achieve the low scattering performance base on the artificial polarized converter.Through the principle of phase cancellation,the mechanism of RCS reduction is clarified.The polarization conversion ratio has an influence on the low scattering performance,and the-10 d B reduction bandwidth of the reflectarray can be improved by increasing the polarization conversion ratio of the unit cell.The relative bandwidth of the-10 d B reduction of the reflectarray is over 96%,and the oblique incidence property of the reflectarray is stable for x and y polarized waves.Secondly,a design method for the generation and convergence of orbital angular momentum(OAM)based on the artificial polarized converter is presented.According to the theoretical of OAM and the phase gradient,MATLAB and CST macro are used to realize the design of the reflectarray which can generate OAM.The phase and amplitude property of the polarized converter are effective to reduce the difficulty of OAM design.By introducing the phase convergence factor,the convergence property of the OAM beam has also been researched,the convergence effect of the beam can be increased by more than 50%,and this has improved the efficiency of the beam in the transmission process.In addition,the scattering property of these two type reflectarrays are also been researched,they can achieve the low scattering performance at the same time under vertical polarization and horizontal polarization.In summary,the polarization property and polarization mechanism has been analyzed deeply,and the application based on the polarized converter is also been researched.The properties of broadband,dual-band,low-frequency,multi-functional and high-efficiency have been explored.The multi-resonance and low-frequency physical mechanism based on transmission matrix theory,equivalent impedance theory and equivalent circuit model have been constructed and researched.The controlling of EM scattering based on the artificial polarized converter has been analyzed,and the low scattering property of the reflectarray is realized.This method can reduce the difficulty of designing this reflectarray and have important significance on the research of polarization property and EM scattering. |
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