Research And Performance Optimization Of Microwave Photonic Frequency Measurement System

With the rapid development of microwave technology,major breakthroughs have been made in satellite communication,electronic warfare,radar,navigation and positioning,wireless communication,and other related fields.In various fields,domestic and foreign scholars have put forward many solutions to the problem of how to achieve high performance measurement of microwave signals.However,due to the need for real-time,accurate,and rapid detection and warning of the surrounding environment in military war,coupled with the gradual broadening of the working frequency band of various radiation sources,flexible frequency and weak effective signals,the receiver is required not only to have ultra-wideband spectrum sensing capability,Moreover,it has significant advantages in measurement accuracy,speed,dynamic range,and resolution.Therefore,this puts great pressure on the traditional microwave measurement system.Based on the above requirements,in order to solve the bottleneck problem that the traditional system cannot break through,microwave photonics is introduced to adapt to the complex electromagnetic spectrum environment,effectively improve the signal recognition efficiency of the receiver,and enhance the military attack and defense capabilities.As a new research field,photonics-assisted microwave technology shows obvious advantages,such as wide frequency coverage,low transmission loss,strong anti-electromagnetic interference ability,so researchers began to apply it in microwave measurement system to achieve excellent performance,to meet the needs of applications.The current microwave photonic measurement system still has many problems,and its performance needs to be further improved.This paper focuses on the microwave photonic frequency measurement system,combines microwave photonic phase shifting technology,spectrum stacking technology,down conversion technology and other technologies,and studies the key problems of frequency measurement range,measurement accuracy,resolution,multi-parameter,multi-frequency signal and dynamic range,which provides a powerful reference scheme for the further application of the microwave photonic frequency measurement system.The main research contents of this paper are as follows:1.Aiming at the significance of simultaneous extraction of phase and frequency information in practical applications,a frequency/phase dual-parameter measurement system combined with stimulated Brillouin scattering(SBS)effect and mapping technology is proposed.Based on SBS effect phase shifting technology,the system changes the phase of the optical carrier by adjusting the frequency of the input signal,and further establishes a flexible and adjustable power response function,so that the measurement range and accuracy of the system can be flexibly reconstructed.In addition,there is a reference signal of phase change in the system,which converts the phase information of the received signal into power information,and finally completes the extraction of the phase and frequency of the received signal.At the bandwidth of 18 GHz,the error of frequency measurement is less than 0.15 GHz,the resolution of phase measurement is less than 0.05°,and the measurement range is0～2π.2.In order to reduce the measurement error of the system,a high precision frequency measurement system based on Brillouin Phase Shift-Gain Ratio(BPGR)is proposed.Based on the correlation between the unknown signal frequency and the known signal gain and phase shift in the system,the monotone increasing BPGR curve is established to further realize the frequency mapping and complete the extraction of the unknown signal frequency information.Because the SBS effect is applied to channel the whole measurement range,the constrained relationship between measurement range and accuracy is broken,and the measurement error is reduced to less than 5 MHz.Under the condition of ensuring the simple structure,the system also can measure multi-frequency signals and relatively good stability.3.In order to meet the requirements of bandwidth in different application scenarios,a flexible and adjustable bandwidth measurement system based on optical frequency comb pump is proposed.The SBS effect is excited by optical comb pump spectrum,and a linear phase shift curve is constructed which is related to unknown signal and the range is adjustable,and the unknown signal frequency information is extracted.More importantly,by simply controlling the number and position of optical frequency combs,the measurement frequency band can be flexibly switched between VHF band,S band,X band and Ku band.The experimental results show that the error is stable below 35 MHz when the measurement bandwidth is switched flexibly.4.In order to solve the problem of limited frequency resolution in multifrequency signal measurement,spectrum stacking technology is introduced to realize the high-resolution measurement system.In the design,a gain spectrum and two loss spectra generated in the SBS process are superimposed to narrow the spectrum carrying unknown signal information,which not only realizes the extraction of unknown signal frequency but also improves the system resolution.This technique reduces the response bandwidth to about 40% of the original,and reduces the system resolution from 30 MHz to 14.5 MHz.In addition,the measurement range of the frequency is doubled by adjusting the initial frequency of the sweep signal while keeping the measurement error is as low as 8 MHz.5.In order to reduce the pressure of subsequent collection and processing,down conversion technology is introduced to realize a high-performance channelized frequency measurement system while ensuring the above performance.In this part,two channelization systems based on space and time domain are proposed.Firstly,the channelized measurement system is constructed by using frequency shifter array in space domain to realize the segmentation and conversion of broadband signals,which has the advantage of instantaneous measurement.Secondly,the channelized measurement system is established in the time domain by introducing the variable reference signal.For the input signal of any frequency,the output of the system can be collected at a fixed low frequency point,avoiding the use of high-speed devices.Meanwhile,the smooth denoising algorithm is used to optimize the noise characteristics and improve the frequency resolution of the system.The channelized system has some advantages in measuring range,precision,time,dynamic range and multifrequency measuring capability,which provides a new solution for improving the overall performance of the RF signal receiving system.