Research And Integrated Design On X-band Polarization System Of Feed Network

A polarization system on radio telescopes generally consists of a polarizer,a waveguide-to-coax adaptor,a directional coupler and etc.Usually,in order to obtain the maximum system sensitivity,the polarization system will be worked at 20 K platform in the cryostat of cryogenic receivers which decreases the receiver noise temperature to lowest.Polarization system,as a passive front end of the radio astronomy receiver,is used to separate cicular-polarized signal from radio source and calibrate receiver,and its performance is crucial to the quality of the receiver signal.Traditional X-band radio telescope receiver are used discrete structure design,polarizer、waveguide-to-coax adaptor and directional coupler are designed or purchased separately,not only bulky,expensive but also have a higher loss.Through in-depth study of the polarization system,this paper designs two X-band(8~9GHz)polarizer、coupler and waveguide-to-coax adaptor integrated structures based on a septum structure.This design not only realizes the conversion of circularly polarized wave to linearly polarized wave,but also obtains the noise coupling of 30 dB.Meanwhile,the integrated design further reduces the cascading between passive devices to get the lowest insertion loss of the feed network in front of the cryogenic low noise amplifier which enhances the receiving sensitivity of the radio telescope.The size of the design is as follow: 100×70×60mm,weight: 0.45 kg.Result of measurement at operating frequency are shown as follow:SMA port reflection coefficients are better than-23 dB,isolation is better than 28dB;The typical coupling coefficient of the directional coupler is 30±1.5dB,the directional coefficient is better than 23dB;The phase shift of polarizer is 87.5~93°,t he axis ratio is less than 0.45 dB;The insertion loss of the polarization network integrated design is 0.17~0.37 dB,it is far superior to the traditional X-band radio telescope receiver insertion loss;...