Research And Application Of Double Balance Detection In Doppler Frequency Shift Measurement

The measurement of Doppler shift is widely used in communication,radar,electronic warfare and remote sensing.However,with the rapid development of microwave technology and communication technology,the traditional doppler frequency shift measurement scheme based on electronic technology is usually limited by instantaneous bandwidth,transmission loss and electromagnetic interference,etc.,and it is more and more difficult to meet the requirements of broadband signal detection.Microwave photonics produced by the combination of microwave technology and photonic technology provides a new idea for the measurement of wideband Doppler frequency shift.The Doppler frequency shift measurement scheme based on microwave photonics has the characteristics of high sensitivity,large dynamic range,large instantaneous bandwidth,high resolution,anti-electromagnetic interference and so on,and has become one of the research hotspots at present.The research and application of double balance heterodyne detection system is very important to improve the performance of Doppler frequency shift measurement scheme.In this paper,the double balance heterodyne detection technology is studied from the following three aspects:1.The research background,significance and implementation of double equilibrium heterodyne detection technology are introduced.The mathematical models of direct detection,ordinary heterodyne detection,balanced heterodyne detection and double balanced heterodyne detection are established by using matrix optics method.The advantages and disadvantages of each model are analyzed,and the signal-to-noise ratio formulas of double balanced detection and ordinary heterodyne detection are deduced.By analyzing the characteristic parameters in the SNR formula,the superiority of double balance detection is proved theoretically.Then,based on the polarization beam-splitting double-balance heterodyne detection theory,a simulation model of the double-balance heterodyne detection system was built by using the Opti System simulation software.The effects of the rotation Angle of the wave plate,the spectral ratio of the polarization beam-splitter and the quantum efficiency of the photodetector on the detection performance of the double-balance detection system during the practical application were analyzed.The optimal parameter setting of double balance detection system is obtained.2.Based on the double balance heterodyne detection technology,a new solution of wideband microwave Doppler frequency measuring receiver is proposed.The solution has wider frequency coverage,higher measurement resolution,higher sensitivity and anti-beat interference performance.The direction of Doppler frequency shift(DFS)can be accurately measured by using a dual balance detection system consisting of a 90° optical mixer and two balance detectors.In the simulation experiment,the DFS is estimated for the transmitted microwave signals from 10 GHz to38 GHz.In the DFS measuring range of-90 k Hz ? +90 k Hz,directional ambiguity is eliminated,and the measurement error is less than ±2Hz.In the actual experiment,an acousto-optic modulator is used to simulate the generated single side band signal.Because the acousto-optic modulator is greatly affected by the environment and temperature,the accuracy is reduced to ±74Hz.3.On the basis of the original circuit,the coherent heterodyne detection method is adopted to design the laser Doppler frequency shift vibration measurement scheme based on double balance heterodyne detection,which is used to measure the vibration generated by the object to obtain the vibration information of the vibration source.The time domain waveform and spectrum diagram output by the scheme show that the system has good detection performance.Similarly,the application of double balance detection technology in this scheme can effectively improve the sensitivity and anti-beat interference performance of the system.