A Study Of Polarization Converter And Its Application

Typically,an antenna has a fixed polarization mode(including circular polarization,linear polarization and elliptical polarization).Sometimes,it is difficult to design an antenna with a specified polarization in some cases(the space-limit condition especially),so it is an effective way to use polarization converter to transform the polarization of the incident wave form the original antenna.The polarization converter is usually used iin the section of radar antenna,so it has an important application prospect in the application of base station antennas.Combining with requirements of the project,we design three polarization converters:a meander-line line-circular polarization converter,a hybrid structure line-circular polarization converter and diagonal line-line polarization converter.In detail,on the basis of polarization transformation theory,we have done the following work:(1)Meander-line line-circular polarization converter:it is printed with 3 layers copper clad incorporating 10 mils thickness and FR4 substrate.Firstly,we use HFSS to design the model,the 3dB axial ratio bandwidth of meander-line linear-circular polarizer is about 44%,the insertion loss less than 1dB and working frequency of 14-22 GHz.Then we change the angles of incident wave,and compare the axial ratio of transmitted waves with different angles to get the proper angles of incident wave.Then process it and test its performance.Using the H plane horn antenna as an example,we can compare the polarization,the beam shape and the reflection coefficient of the antenna when the polarizers are added.(2)Hybrid structure line-circular polarization converter:it is designed with meander-line and patch based on the transmission line theory.Insertion loss of the improved line-circular polarizer is less than 2.5dB,the thickness is reduced by half and the axial ratio bandwidth by 4%compared with the meander-line polarizer at the same time.Then we change the angles of incident wave,and compare the axial ratio of transmitted waves with different angles to get the proper angles of incident wave.Then process it and test its performance.Using the H plane horn antenna as an example,we can compare the polarization,the beam shape and the reflection coefficient of the antenna when the polarizers are added.(3)Diagonal line-line polarization converter:it is designed with the oblique liine structure and the multi-layer different slope of the oblique copper clad plate,changing the vertical polarization to oblique 45° polarization,the working frequency band is 18-26 GHz,the polarization conversion effect is 40°-55° in the working band.Then,a horn antenna is used as an example,we can compare the polarization,the beam shape and the reflection coefficient of the antenna when the polarizer is added.And we compare the polarization transformation effect of the line-line polarizers with 4 layers and 5 layers,and we compare the beam shape and the reflection coefficient of the antenna when the polarizers are added.