Research And Design Of Transmission-type Broadband Polarization Converter Based On Artificial Electromagnetic Structure

With the widespread application of communications,radar,and navigation in modern society,communication equipment has increasingly higher requirements for polarization matching when transmitting and receiving electromagnetic waves.Ferrite or passive circuit is the traditional way to control electromagnetic wave polarization,but it has disadvantages such as large volume,low conversion efficiency and narrow working bandwidth.The polarization converter based on artificial electromagnetic structure has the advantages of light and thin,high conversion efficiency,wide working bandwidth and easy to integration.Due to its many advantages,it has gradually become a research hotspot in recent years.In this paper,the polarization converter based on the artificial electromagnetic structure is researched and designed,the mechanism of the polarization conversion of the artificial electromagnetic structure is analyzed,and the broadband high-efficiency linear-to-circular polarization converter and the reconfigurable linear-to-linear polarization converter are designed.The designed polarization converter was verified by experiments,and its influence on the radiation performance of the horn antenna was analyzed.The main research content and work of this paper are summarized as follows:Firstly,in order to solve the problem of narrow working bandwidth of the linearto-circular polarization converter in the S and C bands,a broadband transmissive linearto-circular polarization converter working in the S and C bands was designed.The metal structure on the front of the unit is a symmetrical U shape,and the back is a continuous spiral.When the linearly polarized wave is incident vertically,the insertion loss of the proposed linear-to-circular polarized converter is less than 0.9 d B in 2.5-5.6GHz,and the axial ratio of the transmitted wave is less than 3 d B.When the linearly polarized wave is incident obliquely within the range of ±30°,the designed device also exhibits stable operating characteristics.The experimental results are close to the simulation results,which indicate the effectiveness of the designed linear-to-circular polarization converter.Secondly,in order to adapt to the trend of device miniaturization,improve the practicability of the designed polarization converter,based on the existing polarization converter,a thinner linear-to-circular polarization converter that also works in the S and C bands is designed.By replacing the middle two layers of the original multilayer structure with new layers that are capacitive in two orthogonal directions,and then comprehensively considering multiple parameters of the entire device for numerical simulation and optimization,the layer spacing of the polarization converter can be reduced to half of the original,and the total thickness of the device can be reduced to about half of the original.Compared with the original device,the polarization conversion bandwidth of the newly designed device is basically unchanged.The total thickness is reduced from 62.54 mm to 27.52 mm,which is 44% of the original device.The designed linear-to-circular polarization converter can expand the types of polarization waves that can be transmitted or received by existing antennas,and it can be used in communications,radar,navigation and other fields.Finally,a controllable cross linear-to-linear polarization converter loaded with PIN diodes is designed based on the transmission-type artificial electromagnetic structure.The simulation results shows that within 5.52-6.54 GHz,the designed cross linear-tolinear polarization converter has polarization maintaining function when the PIN diode is turned off,and polarization conversion function when the PIN diode is turned on.The insertion loss of the designed device in the working frequency band is less than 1.5d B,and the polarization isolation in the working frequency band is above 20 d B.When the device is in the polarization conversion state,the PIN diode is set up with two diodes in parallel on each unit,and then connected in series with other units in the x-axis direction.This design can not only improve the working reliability of the polarization converter,but also enable the converter withstand stronger microwave radiation power.