Research On U-Band Cryogenic Reception Front-End Technology

In the fields of wireless communication,navigation guidance and space exploration,the application of millimeter wave technology in the receiving system can alleviate the spectrum tension and improve the system index.In order to further improve the performance of the receiving system,a U-band cryogenic receiver front-end subsystem is designed and implemented by combining vacuum cryogenic and microwave/millimeter wave circuit technologies.The system works in liquid helium cryogenic environment and is mainly composed of low noise amplifier,multi-mode filter and vacuum sealing device.According to the difference of U-band low-temperature receiving front-end system architecture,the design of cavity filter and plane filter is completed.According to the different connection modes of the input terminal in the front system cavity,the waveguide and cable connection schemes are designed.Combined with the requirements of low noise factor of the system and flexible and simple microwave link assembly,the system uses air coaxial structure for connection at the input end and cavity structure filter is selected for filtering circuit,that is,coaxial cable is used to connect the waveguide and filter at the input end to form back-to-back structure.The development of passive components of the system mainly includes the design of sealed window,waveguide-coaxial transition structure and cavity multimode filter.The simulation results of the sealed window and the waveguide-coaxial transition structure meet the requirements of the index.Aiming at the frequency response of the resonator in the filter,the simulation design of two cavity multi-mode filters is completed.By comparing the ridge resonator filter and the waveguide with better performance,the back-to-back structure design is carried out.Finally,the processing of the filter with passband f₁-f₂ and the test at different temperatures are completed.The development of the system active device mainly includes transition circuit and low noise amplifier circuit.The transition circuit uses waveguide-probe-microstrip structure,and the simulation,physical production and back to back structure test are completed.The development of low noise amplifier needs to complete the chip selection and stability,matching circuit and gain analysis according to the requirements,and then add the feed box body on the basis of the probe box body and carry out S-parameter simulation,and finally complete the processing,assembly and testing of low noise amplifier under different temperatures.According to the overall design of the system,the microwave link is assembled and tested.Finally,a U-band low-temperature receiving front-end subsystem is obtained.The test data at the temperature of 290K are as follows:the in-band gain is 9.5-11.3d B,and the return loss is better than 8.5d B.The test data at 20K temperature are as follows:the in-band gain is 13.6-15.9d B,the standing wave coefficient is better than 2.3,and the noise coefficient is better than 3d B,which basically meets the design specifications of the whole machine.