Research On Frequency Measurement Technology Based On Microwave Photonics

Modern wars have gradually evolved into information-based wars.The initiative to grasp information is an important guarantee for victory in the war.Instantaneous frequency measurement(IFM)is one of the key technologies of electronic warfare.By quickly and accurately acquiring the frequency information of the target,the purpose of investigation,early warning and interference can be achieved.And doppler frequency shift(DFS)and angle of arrival(AOA)measurements can be used to accurately track the speed and position of moving targets in radar and wireless communication systems.The traditional electrical domain parameter measurement system has a limited measurement range due to electronic device speed bottleneck,and it performs poorly in a complex and changeable measurement environment.However,the photonics-assisted measurement technology has received widespread attention in recent years for its inherent advantages such as small size,light weight,low insertion loss,and strong resistance to electromagnetic interference.This article first summarizes the research background and current status of the subject,and then on the premise of researching the related technical principles and device principles,a microwave photonics-based instantaneous frequency measurement scheme and a simultaneous measurement scheme of the doppler shift and angle of arrival of microwave signal are proposed.The feasibility of the two schemes was verified by simulation.The main research work and innovations of this paper are as follows:(1)On the basis of the research of instantaneous frequency measurement technology based on microwave frequency-amplitude mapping,an instantaneous frequency measurement scheme with adjustable measurement range based on an an electro-optical polarization modulator(PolM)is proposed.In this scheme,different polarization processing is performed on the upper and the lower branches,and the single-mode fiber is used to introduce dispersion to the upper and lower branches,so that the frequency information of the signal under test is mapped to the phase information caused by the dispersion,and then the amplitude comparison function(ACF)is constructed by the photocurrent amplitude.It can be seen from the theoretical analysis that the frequency of the signal under test has a linear relationship with the ACF,so the frequency of the signal under test can be derived from the ACF,and the system measurement range in this scheme can be adjusted by adjusting the bias voltage and the polarization angle of the lower branch.The simulation results show that by optimizing the dc bias voltage and the polarization angle of the lower branch,the system obtains a maximum frequency measurement range of 3-42.8GHz.For microwave signals above 3GHz,the measurement errors are kept within 0.1 GHz.The proposed scheme only requires one single polarization modulator and one single laser source,the system structure is simple,and the system measurement resolution can be improved by optimizing the slope of the ACF.(2)Based on the research of doppler frequency shift measurement technology and angle of arrival measurement technology,a scheme for simultaneous measurement of doppler frequency shift and angle of arrival based on microwave photonics is proposed.In this scheme,the lightwave carrying the information of the echo signal and the lightwave carrying the information of the local oscillator(LO)are mixed,and then the upper sideband and the lower sideband of the mixed signal are separated into two channels and converted to electrical signals.From the theoretical analysis,the parameters of DFS and AOA can be obtained by processing two low-frequency photocurrents,and the direction of DFS can be confirmed by comparing the phase difference of the two electrical signals.The simulation results show that the system can measure DFS in the range of±100kHz,and the errors are less than±8×10-6Hz,and the system can measure AOA in the range of 1.82°-90° with the errors not exceeding 0.9°.In the proposed scheme,the upper and lower sidebands of the optical signal are separated by a wavelength interleaver(IL),which can simplify the system structure.