Research And Design Of The Microwave Cavity In The Rubidium Atomic Frequency Standard

The rubidium atomic frequency standard?or rubidium atomic clock?is an atomic frequency standard with a simple structure and strong stability,it has a wide range of applications in navigation,communications,and other fields.As the core component of the rubidium atomic clock,the resonant characteristics of the microwave resonant cavity determine the stability of the rubidium atomic clock.Based on the horizontal project"Development of uniform field microwave cavity",the research and the design of the resonant cavity of the rubidium atomic clock are developed.By analyzing the resonance theory of the cylindrical resonant cavity,the design method of the general cylindrical cavity is obtained.According to the design index,the resonant cavity required is designed;meanwhile,as the connecting part of the microwave cavity,the performance of the coaxial connector has a certain influence on the performance of the rubidium atomic clock.For this purpose,a coaxial connector that meets the system requirements is designed.In this thesis,the resonant characteristics of cylindrical cavity are analyzed in detail.The field theory of circular waveguide that constitutes the cylindrical cavity is discussed,the field equations and the electromagnetic field distribution of the cylindrical waveguide are derived by using the scalar function.Based on the circular waveguide field equation combined with the boundary conditions of the end surface,different modes of electromagnetic field distribution in the cylindrical cavity are obtained,also,the method for calculating the resonance frequency and quality factor in the resonator is analyzed.The proper excitation method is a necessary condition for the stability of the resonator's operating performance.For two commonly used excitation methods:ring coupling and hole coupling,this thesis analyzes in detail the effects of the two coupling methods on resonant performance of resonators.These theories above play an important guiding role on the selection of coupling modes of the resonator,the design of the size and position of the coupling structure.Secondly,the design method of cavity and coaxial connector is studied in detail.The stable transition of the rubidium atomic in the resonant cavity requires the uniform distribution of the magnetic field,therefore,the resonant cavity of the TE₀₁₁ mode is selected as the atomic transition site.In order to suppress microwave leakage,a cut-off waveguide structure with a shielding effectiveness of 103dB is designed,the analysis of the filling factor helps to obtain the size and structure of the cut-off waveguide.The model matching method is used to deduce the theory of reentry cavity which loading cutoff waveguide,thus,the coefficient calculation matrix of the reentry cavity field equation is obtained,then the field equations of reentrant cavity can be obtained.In order to obtain the desired uniform field,a secondary coupling structure is designed.The probe is coupled to the rectangular cavity,and then the energy is sent into the reentry cavity through the symmetric double-slit coupling.The stable transition of the rubidium atomic under the uniform field is achieved.The simulation results of the designed resonant cavity by using HFSS,meet the design requirements.Based on research of the coaxial line theory,the design method of the coaxial connector is obtained,and the discontinuity and compensation method of the coaxial connector are discussed.A 5GHz-8GHz coaxial connector was designed with the axial misalignment compensation structure.The middle part of connector is filled with ceramic materials with better compactness.Simulation and test results show that the performance.Finally,processing the resonant cavity with Ti alloy?TC4?and testing the designed resonant cavity system,the results meet the design requirements.Several factors affecting the frequency are introduced.