Research On Phase Stable Transmission Of Rf Signal Based On Microwave Photonics Technology

Compared with coaxial cables,optical fibers have advantages such as low loss,low cost,and immunity to electromagnetic interference.In the past several decades,the use of optical fibers to transmit radio frequency signals has been widely studied and applied.However,due to the characteristics of the optical fiber itself,it is easily disturbed by the environment(such as temperature change,mechanical vibration),resulting in a change in transmission delay,which causes the phase of the RF signal loaded on the light wave to fluctuate accordingly.In this dissertation,firstly,the scheme of the stable phase transmission system of RF signal fiber is analyzed in recent years,and it is concluded that there are some problem in the current phase stability transmission method,such as phase stability accuracy is not high enough,the signal transmission bandwidth is limited,and the phase of the RF signal after phase stabilization still have residual noise,followed by analysis of the causes of such problems,and finally proposed a corresponding solution.In this thesis,aiming at the current phase stable transmission method based on the principle of round-trip compensation,the phase comparison link is limited by the electronic bottleneck,the working bandwidth is narrow,and the detection of the phase difference between high-frequency signals is faced with low accuracy.Based on the microwave photonic technology,the A novel method of frequency-shift heterodyne phase comparison is proposed.The feasibility of the method is verified by theoretical analysis and experiments.The phase comparison method based on the frequency heterodyne only requires the use of a low-frequency phase detector.By comparing the phase differences of the two low-frequency electrical signals,the phase jitter introduced by the optical-borne radio frequency signal in the optical fiber can be obtained.Since the phase difference is shifted from the high frequency to the low frequency signal,the accuracy of the phase difference detection is improved.Since this solution does not require broadband photodetectors and high-frequency phase detectors,only corresponding low-frequency devices can be used,thus reducing system costs and increasing the system's operating bandwidth.This dissertation proposes a new phase-stabilization scheme for the current stationary phase transmission method based on the principle of mixing elimination,the structure of the system is complex and the problem of residual phase noise in the RF signal output from the remote end after phase stabilization.The principle of work and advantages,then discussed in detail how each module should be optimized,and finally based on this program actually built a stable phase transmission system,to achieve a stable phase of the 2.4GHz signal transmission,transmission fiber length of 10.25 km.In the 50-minute measurement period,the peak-to-peak value of the signal delay change was reduced from 280.77 ps for free transmission to 41.93 ps for phase stabilization,and the single-sideband phase noise was reduced from-61dBc/Hz@1Hz to-87dBc/.Hz@1Hz,-70dBc/Hz@10Hz is reduced to-80dBc/Hz@10Hz.In 80 seconds,the adjustable optical fiber delay line was adjusted from 0ps to 80 ps slowly and uniformly,and the peak-to-peak value of the signal delay variation was reduced from 92.76 ps for free transmission to 8.93 ps.The system has the advantages of relatively simple structure and high stability,but some modules still need to be improved.