Research On Passive Hydrogen Clock RF Channel Characteristic Parameters And FPGA Implementation

As a stable high-precision time-frequency standard,passive hydrogen atomic clocks are currently deployed in some of the core components of the "Beidou ?" project.Nowadays,with the vigorous development of aerospace navigation and positioning technology,the performance indexes of passive hydrogen atomic clocks need to be continuously improved.The Shanghai Astronomical Observatory of the Chinese Academy of Sciences has complete experimental facilities and instruments,which provide excellent conditions for scientific research experiments.Aiming at the current delay parameter estimation of passive hydrogen clock and the performance of hydrogen atom transition signal has not been optimized,this paper proposes a time delay index estimation algorithm based on passive hydrogen clock and a method to find the optimal input power point of hydrogen clock based on system signal-to-noise ratio is proposed in this paper.In this method a complete model of digital circuit system is built through the FPGA chip XC4VSX35 produced by Xilinx,combined with the B2209 chip,B9764 chip and B9243 chip produced by China Aerospace Research Institute,plus various functional devices.Through the combination of software simulation and hardware implementation,the performance parameters of the passive hydrogen clock are optimized,and the time-frequency accuracy of the passive hydrogen clock can be improved.Firstly,for the Gaussian random signal,the traditional passive hydrogen clock delay estimation method will cause performance degradation.Therefore,a passive hydrogen clock delay estimation method based on least squares sample fitting is proposed.By giving the cost function of cross-correlation,the cost function is minimized by using the sine interpolation formula and the least squares criterion,and the unbiased estimation value is obtained and approximated,and the lower Cramer-Rao Lower Bound is given.The cross-correlation algorithm and the minimum mean square error algorithm are used to compare the simulation performance with the proposed algorithm in this paper.Finally,the estimated delay is calculated and the corresponding curve is drew by the hardware system model.The feasibility and effectiveness of the algorithm are successfully verified.In addition,based on the existence of improvement space in the current passive hydrogen clock performance,with the characteristics of hydrogen atom level transition,a method for finding the optimal input power point of hydrogen clock based on system signal-to-noise ratio to improve the performance of atomic transition signal is proposed.First,the equal-amplitude sine sweep signal is obtained by the digital frequency synthesizer and introduced into the hydrogen clock cavity to obtain the amplitude-frequency characteristic of the cavity.Then,by controlling the varactor voltage and the crystal voltage control voltage in the resonant cavity,the maximum atomic transition signal energy can be achieved,and the hydrogen clock physical output signal is calculated and analyzed by the circuit system model after down-conversion.The signal bandwidth and system signal-to-noise ratio curve of the atomic transition signal is obtained under different input powers,and the optimal input power point is found to improve the performance of the atomic transition signal.Finally,it is successfully verified by comparing with another test hydrogen clock.Finally,the contents and conclusions of this paper are summarized and the future prospects is given.By the experimental research work of this paper,a method reference is provided for the research direction of passive hydrogen clock.