| The optical carrier-based microwave interferometry（OCMI）technology combines the advantages of optics and microwave interferometry,and has great advantages in low-cost,long-distance transmission and directional high-precision ranging.In order to realize the engineering application of OCMI in ranging scenarios,it is necessary to propose a new demodulation method which is lower-cost and easy-to-use.Therefore,this article mainly focuses on the research of the demodulation of the OCMI ranging signals.A demodulation algorithm and system have been proposed,and several experiments have been arranged to verify the effectiveness and stability of the demodulation algorithm.The main content of this paper is as follows:（1）The theoretical formula of OCMI is further calculated.A comparative study of several phase demodulation algorithms including correlation method,Fourier transform method,least square method and Hilbert transform method has been done.A demodulation method based on Hilbert transform has been established.Considering the high-frequency characteristics of the microwave envelope,the overall structure of the demodulation system is designed,and the functions of each part are sorted out.（2）Based on the Hilbert transform method,several key technologies of the OCMI phase demodulation have been studied.The demodulation consists of data fitting algorithm,down-conversion method and frequency modulation defuzzification algorithm.A contrast link is designed in the demodulation system to decrease the phase error introduced by the system components.The theorical accuracy and the measuring range of the demodulation system has been analyzed.（3）The system is realized according to the functional requirements of the demodulation link.Two microwave sources have the same phase,and the frequency changes synchronously.The 12bit analog-to-digital conversion chip AD9613 with an upper limit of 250Msps sampling rate is used for sampling,and PCB board has been designed.Zynq-7020 is used to realize the logic path of discrete signal transmission and filtering.（4）The experimental platform is set up for length-measuring to verify the feasibility of the algorithm.The experimental platform is pre-processed according to the characteristics of the optical fiber,and the calibration link is designed.Three experiments have been designed to verify the effectiveness and stability of the demodulation algorithm.The result shows that when the maximum microwave modulation frequency is set to 1.5 GHz,the standard deviation of the measured data can be limited to the level of 10-5. |
