Automatic Tracking Technology Of Center Frequency Of Selective Frequency Amplifier In LRCS System

In the measurement of laser radar cross section(LRCS),the echo signal is very weak,and the measurement system is easily affected by the environment,the background noise and the receiving system noise,greatly increasing the difficulty of measuring LRCS.To suppress interference of the background light,the receiving system should select a high Q value selective amplifier.However,the R and C values in the high Q value selective amplifier can be changed by the surrounding temperature,this can strongly impact on the detection results.In addition,the high Q amplifier is much sensitive to the modulation frequency fluctuation of the light source.Moreover,the central frequency of the selective amplifier is not a measurable quantity.It is difficult to compare it with the modulation frequency of the laser.Therefore,the amplifier system should have high Q value,and the measured results should not be influenced by the change of the environment or the fluctuation of the frequency of the light source.This thesis proposes a novel compensation technique to remove the influences on the receive system owing to surrounding factors and the fluctuation of the modulation frequency of the transmitted laser.In the thesis,we introduce the system structure,working principle and related applications of laser ladar,and the definition and measurement principle of laser radar cross section.Principles and calculation methods of comparative measurement method of laser radar cross section are presented in detail.The echo optical power are also estimated.In the thesis several kinds of filters are compared,we choose the biquadratic active band-pass filter as the receive system,which has the advantages of good stability,easy adjustment.The circuit theory,design method and sensitivity of the biquadratic active band-pass filter are discussed in detail.To meet the requirement of practical application,we develop a biquadratic active band-pass filter,in which the central frequency can be adjusted automatically.Based on the adjustment principle of the central frequency of the biquadratic active band-pass filter,the simulation experiment is carried out.According to the simulation results,we design the receive system circuit and PCB,and the experiment is also made.In this receive system aprogrammable resistor is used as the adjusting device to adjust the central frequency of the filter.The MSP430G2553 single chip computer and the AD8400 digital programmable resistor are selected to realize the automatic tracking system.The working principle of the single chip microcomputer MSP430G2553 and the digital programmable resistor AD8400 are presented.Experimental and simulation results show that the central frequency can be well tracked automatically,and the output signal of the receive system can not changed when the input signal frequency of filter fluctuates and the surrounding temperature varies.