Design Of Dual-polarization Microwave Radiometer Receiver

Widely used in environmental monitoring,biomedicine and public safety,polarized microwave radiometers can provide the radiation information of target polarization.So it is of great significance to study polarized microwave radiometers in this paper.Firstly,on the basis of introducing the related principles of polarized radiation measurement and polarized radiometer,the receiver system structure of the dual-polarized radiometer is designed,and the radiometer's parameters are calculated theoretically.Secondly,the basic theories of orthogonal mode coupler(OMT)and waveguide are studied.An OMT with a simple structure and convenient adjustment is designed and simulated.Besides,simulation results show that the return loss of single-mode port is less than-15 d B and the port isolation is more than 60 d B;Transmission loss is less than 0.33 d B;The cross polarization ratio is more than 25 d B.Thirdly,based on the principle of reflector antenna,aperture field distribution and feed antenna,two types of antenna feed systems are designed in which the feed antenna is integrated with OMT.And the systems use radial and axial grooved corrugated horns,and are compared by simulation results.Using the technology of 3D printing and surface metallization,the axial grooved antenna feed system is realized and its simulation result shows that the total gain reaches 14.6d B;The return loss at port 1 is less than-20 d B and port 2 is less than-13 d B;The single port isolation is greater than 60 d B;The cross polarization ratio is greater than 30 d B;Edge taper level is less than-10 d B.Finally,the intermediate frequency amplification,detection,low frequency amplification and power supply circuit of the radiometer receiver system are designed,and the surface,asphalt pavement and grassland observation experiments of polarization radiometer receiver system are carried out.The experimental results compared with simulation shows that the reflectance at different angles is basically consistent with the simulation results.