Research On Frequency Decreasing Of Beat Signal Of FMCW Ladar Measuring

In the field of absolute distance measuring, FMCW(Frequency Modulated Continuous Wave) Ladar(Laser Radar) gains widespread utility for its extensiveness,rapidity, high-precision, not having measure blank areas and a lack of dependency on target drone. Though, neither a leading nor a frontier technology FMCW Ladar(laser radar) was in developed countries, it is truly just begin in China.FMCW Ladar gives the range of the target by measuring the frequency of the beat generated by the superposition of transmitting wave and echo wave. Usually, this is a high frequency, and it increases as the distance of the target furthers. To adapt the demands of the rapidity of measuring, some measures must be taken to decrease the frequency of the beat precisely and flexibly from the source.Many methods to decrease frequency there were, few of them meet our needs.Fortunately, a new method of frequency decreasing was found and proven to be applicable to decrease the frequency of the beat signal by designing a multiple reference path, which endeavors in the design of the light path and the algorithm. By using an analog low pass filter as well as a special selected parameters of multiple reference path, the method can successfully reduce the frequency of the beat signal, and by using the special selected parameters as well as a method of bandstop of beat signal,it also solved the problem of multiple value and erroneous judgement cause by a multiple reference path, and it meet the actual demands of the measuring.A detailed comparison and analysis between using a light switch to switch from different reference paths and separating the spectrum of different paths directly by using special algorithm was done in this chapter. Also, a thorough design flow method and process was introduced and concluded, as well as a relative experiment, to testify the later method told above. At last, a 4 reference paths combination was designed, and successfully applied to reduce target frequency to less than 1.7MHz, while caused no erroneous judgement in quite a short time.