Research And Design Of FMCW Radar Material Level Measuring Instrument

Linear Frequency Modulation Continuous Wave (FMCW) radar has its own goodfeatures. For example, its transmission is not influenced by the components, density, pressure,temperature and other elements of the air dielectric. Therefore, it’s widely used in variousareas. Distance measurement is considered as one of its basic applications. And the accuracyof high distance measurement is increasingly required in many kinds of fields. However, thedistance accuracy of FMCW radar is limited which is influenced by many factors. The mainfactors include:(1) Noise. In application, noises are always involved in differential frequency signals ofFMCW radar echo wave, which containing miscellaneous waves from space，noises frominternal system and so on.(2) Linearity of voltage-controlled oscillator (VCO). In common VCO frequencymodulation, the method of changing the oscillation frequency is that voltage-controlledvariable reactance component connects to the oscillator. In application, the electronicadjustable frequency of VCO is nonlinear with the electronic adjustable voltage.Focusing on the problems above, linear revisement of VCO, noises management anddesign of FMCW radar’s hardware system were completed basing on the deep analysis ofFMCW radar distance measurement theory in this dissertation. Main points included asfollows:(1) The noise influence on the distance accuracy of FMCW radar was analyzed andsimulated. The method of small wave threshold noise reduction was used in disposal ondifferential frequency signals of echo wave. The results of simulation demonstrated that noiseratio of echo wave signals could be improved through this method.(2) The influence of VCO linearity on the distance accuracy of FMCW radar was alsoanalyzed. Multiple VCO linearity correction schemes were stated, such as the reactancecompensation, open loop and closed loop linearity correction scheme. Advantages anddisadvantages of every linearity correction method were concluded. In this paper, the methodof digital closed-loop linearity correction was chosen to correct the system’s VCO linearity.The results showed that VCO linearity of modulation frequency could be improvedeffectively.(3) According to the requirement level of FMCW radar system, M430single-chip, CPLD,DAC and other components were utilized to design the hardware system of swept signalgenerator. The software was designed by using Visual C and VHDL.(4) Test the FMCW rada level system and analyse the results.