Design Of Absorbing Coatings/Metamaterials And Their Applications In Circular Polarized Antennas

Pollution generated by electromagnetic radiation will cause serious harm to human body.Electromagnetic wave may also lead to information leakage.Therefore,there is a great significance and necessary to study electromagnetic radiation protection and prevent electromagnetic wave leakage.Due to electromagnetic waves are transmitted and received by antennas,the chance of the antennas' parameters will cause other undesirable performance changes of the antennas.The introduction of absorbing materials/coatings can solve some technical bottlenecks encountered in traditional electromagnetic wave design.However,existing microwave absorbing coatings are heavy and thick,narrow bandwidth and not well conformaled with the electronic devices,most of them operated in the lower frequency bands and moreover,the electromagnetic parameters of the coatings can not be designed,which limited their applications.Metamaterials/metasurfaces are intelligent materials which can solve the above problems,metamaterials/metasurfaces are artificially designed structures and have supernormal physical properties,and these properties are not possessed by natural materials.In addition,metamaterials/metasurfaces have good properties.Added the metamaterials/metasurfaces to the antennas will improve the bandwidth or obtain circular polarization of the antenna.Therefore,the development of metamaterials/metasurfaces design and its application in the field of multi-band and broadband antenna has great theoretical and practical value for promoting the development of absorbing materials and radio science.Based on the preparation of different components of microwave absorbing coatings and the design of different structures of metamaterials/metasurfaces,combined with the antenna types designed in this paper,we find out that metamaterial structures are suited for modern communication systems for multi-band,broadband and circular polarization antennas.The metamaterials/metasurfaces are applied to the antenna applications to explore the electromagnetic properties.Adding metamateirals/metasurfaces can broaden the antenna bandwidth and the conversion of linear to circular polarized will be realizedwithout deteriorating the other performances.The main works and creative achievements of the author are as follows:1.Three kinds of high absorption broadband composite absorbing coatings were prepared.They are ZnO whisker/organic silicon composite absorbing coating,Mg2Y magneto plumbitetype ferrite material/E44 epoxy resin and EP curing agent composite wave absorbing coating,carbon nanotubes/cobalt ferrite composite absorbing coating.When the thickness of these three kinds of absorbing coatings are 2mm,2mm and 1mm,the absorbing bandwidth is 13GHz(55 GHz to 68GHz),4.1 GHz(12.4 GHz to 15.5GHz)and 3.1GHz(14.9 GHz to 18GHz),respectively.The factors affecting the absorbing properties of the three kinds of absorbing coatings are studied,such as the mass ratio,the thickness of the coating and the calcination temperature.The absorbing mechanism of the coating was analyzed by using the Maxwell equation and the boundary conditions,and the coating parameters were designed by using Matlab software.2.Ultra wideband absorbers based on metamaterials/metasurfacesare designed in different frequency bands.A metamaterial absorber works in THz band is designed,the frequency band with an absorbing rate larger than 90%is from 0.98 THz to 2.64 THz,and its relative bandwidth is 91.7%,the frequency that the absorbing rate of themetamaterial absorberexceeds 80%in GHz is from 4.97 GHz to 11.27 GHz,and its relative bandwidth is 77.6%,while the double-layer dielectric metamaterial absorber,it's frequency band of absorption exceeds 80%is from 5.18 GHz to 15.7 GHz,and the relative bandwidth is 101.1%.Then a polarized converter based on the metasurface is designed.The converter can realize linear to circular polarization from 3.99 GHz to 4.03 GHz,4.96 GHz to 5.28 GHz,6.07 GHz to 8.78 GHz and 11.07 GHz to 18.29 GHz,respectively,and converts the linear polarization into the cross linear polarizatin from 5.41 GHz to 5.9 GHz and 9.12 GHz to 10.69 GHz,and PCR(Polarization Conversion Ratio)is greater than 80%.3.Three circular polarization antennas are designed with three different circular polarization techniques.The high isolation wideband MIMO(Multinput and Multioutput)circularly polarized antenna achieves the working bandwidth of 1.7 GHz to 6.8 GHz when meeting |S11|<-10dB and |S21|<-14dB.When the |S22|<-10dB,the bandwidth of 2.2 GHz to 7 GHz is obtained,and the circular polarization bandwidth of 42.5%and 4.1%,18.2%,11.1%and 2.3%is obtained with the different feeding ports.The C parasitic patch antenna is loaded with the impedance resonant bandwidth of 117.3%,the measured 3-dB AR(Axial ratio)bandwidth is 32.2%and 3.8%,respectively.The UWB(Ultra Wide Bandwidth)microstrip antenna is designed with slot elliptical parasitic patch and LRH(Left-Right hands)unit achieves 107.9%of operating bandwidth and 69%of the 3-dB axial bandwidth.4.The absorbing coatings/metamateriasl are combined with the antennas.The circular polarization antenna is combined with the Mg2Y magneto plumbitetype ferrite material/E44 epoxy resin and EP curing agent to improve the working bandwidth of the antenna.Then the metamaterial is loaded on the slot antenna and the broadband antenna to realize the circular polarization transformation of the antenna,and the SHSP(Split Octagon Linked by a Square Patch)slot antenna covers 6.35 GHz to 7.1 GHz of AR band,the resonant frequency band is 6.31 GHz to 7.12 GHz,the SHSP broadband antenna covers 2.4 GHz to 3.32 GHz and 6.35 GHz to 7.1 GHz of AR band,and the impedance resonant frequency band is 1.68 GHz to 6.69 GHz,the wide angle circular polarizations in three dimensions are realized.