The Research On Frequency Measurement Technology Based On Microwave Photonics

In modern warfare,the right to control information is an important guarantee for winning the war.As a critical technology of electronic warfare,instantaneous frequency measurement technology can be used to acquire information on enemy electromagnetic radiation accurately,then achieve detection,interference,attack and other purposes.With the increasing complexity of the battlefield,the traditional frequency measurement techniques cannot meet the needs of modern electronic warfare due to limitations such as electronic bottlenecks.As a new interdisciplinary discipline,microwave photonics combines the respective advantages of optical communication technology and microwave technology,which has great potential for development.The microwave photonics system has many advantages such as low loss,wide bandwidth,and strong immunity to electromagnetic interference.The use of microwave photonic technology to achieve instantaneous frequency measurement overcomes many restrictions in traditional technologies,become the focus of current research.This paper mainly studies the frequency measurement technology based on microwave photonics.According to the frequency-power mapping technology,two kinds of microwave photonics frequency measurement schemes are proposed.The measurement parameters,measurement accuracy and other related parameters are studied for different schemes.the results are verified by VPI and MATLAB software.The major work and innovations are as follows:1.The microwave photonics frequency measurement scheme based on PM and MZM combined with dispersive fiber is studied.The factors influencing the effect of frequency measurement are analyzed,and the error in the 2-13 GHz frequency range is kept in the ±0.3 GHz.The disadvantage of the scheme is that the dispersion optical fiber is used in the frequency measurement,which reduces the tunability of the actual frequency measurement.A frequency measurement scheme based on Mach-Zehnder optical filter and a polarization modulator is proposed for the shortcomings of the above scheme.The scheme uses polarization modulator and polarization controller to realize the function of intensity modulation and phase modulation.The amplitude comparison function(ACF)related to the frequency to be measured is constructed by using the power transmission characteristic of the Mach-Zehnder optical filter,and then the frequency measurement is realized.Compared with the frequency measurement scheme which simply uses the dispersion medium to produce power attenuation,the tunability of the scheme is higher.The dynamic adjustment of frequency measurement range and measurement precision can be realized by changing the difference time delay value of the filter.The theoretical verification is carried out by MATLAB software,in which the range of frequency measurement can be obviously improved when the difference time delay value changes from 94 ps to 54 ps.In practical applications,the optimal frequency range corresponding to the difference time delay values can be comprehensively used to measure the frequency.The feasibility of frequency measurement is verified by VPI.The error is kept at ±0.35 GHz in 11-16 GHz frequency range,which indicates that the scheme has a good reference value.2.A frequency measurement scheme based on a fiber grating filter and a polarization modulator is designed.In the scheme,a fiber grating with frequency diversity,low loss,good reflection characteristics and easy system integration is used as a filter to implement the frequency measurement function.The microwave signals are loaded on the optical carrier through the polarization modulator.The intensity modulation function can be realized by adjusting the polarization angle through the polarization controller.The polarization modulator avoids the offset point drift caused by the intensity modulator directly and improves the stability of the system.The modulated signal is divided into two signals through the coupler,one of which passes through the optical filter and the other signal passes through the dispersion fiber.The two signals are finally converted by a photodetector to realize photoelectric conversion.The mathematical expression of the frequency and power of the microwave is constructed by the output power of the two signals.In the experiment,the accuracy of frequency measurement can be chosen by adjusting the reflectivity of fiber grating filter.By VPI simulation,the measurement accuracy can reach ±0.3 GHz in the measurement range of 12-18 GHz.