| With the development of communication technology,the new generation of communication frequency band has covered the millimeter wave range.Due to its advantages of good directionality,narrow beam width,and high reliability,millimeter wave has shown high research value and application prospects in wireless communication technology.In millimeter wave wireless communication systems,conventional passive or active mixers have problems of high noise,low efficiency,and high frequency conversion losses,which restrict the development of millimeter wave communication technology towards high gain,low noise,and low LO power.The superconducting Josephson junction(JJ)has extremely high nonlinearity after entering the superconducting state,and has the advantages of high sensitivity and low noise.It is an ideal element for preparing mixers.Based on the study of the Josephson effect and superconducting junctions,thesis designed and fabricated a millimeter wave mixing system based on Josephson junctions,with RF frequencies ranging from 33 to 35 GHz,LO frequencies ranging from 31 GHz,and IF frequencies ranging from 2 to 4 GHz.Using existing laboratory equipment,a complete testing system was built,and experimental research and theoretical calculations were conducted.In terms of theory,this thesis starts with the basic principles of mixers,analyzes the main indicators of mixers one by one,and focuses on introducing the frequency conversion loss,efficiency,and noise figure of mixers.In addition,the advantages and disadvantages of passive,active,and superconducting mixers were analyzed,and the advantages of superconducting Josephson junction mixers in millimeter wave communication were highlighted after comparison.Finally,the basic theory of Josephson junctions was introduced,including the Josephson effect,equations,and equivalent circuit model.In terms of mixing system development,this thesis first selects the preparation process of the Josephson junction,and then determines a feasible system plan based on the basic theory of the junction.Then,a mixing system based on superconducting junctions and its improvement scheme were designed using electromagnetic simulation software.The preliminary plan is to irradiate and receive the Josephson junction through a transceiver antenna group,with the remaining circuits distributed on both sides of the junction;The improved solution is to use coaxial and microstrip transmission methods to feed the signal into the junction for frequency mixing,reducing the difficulty of processing and measurement,and making the circuit reusable.After processing and assembly,a testing system is built using laboratory equipment such as vector networks,frequency sources,and low-temperature vacuum platforms.Each module is tested separately,followed by overall testing.A Josephson junction with a critical current of100 u A was tested in a low-temperature environment of 20 K.When the local oscillator power is set to-25 d Bm,the minimum frequency conversion loss and minimum noise coefficient measured are 11.45 d B and 6.39 d B,respectively,which preliminarily verifies the nonlinearity of the results. |
