Affection Of VCO And Echo On FMCW Radar System For Displacement Measurement Of Large Infrastructure

Large buildings are the foundation of national economy. It will be a great loss if there was an accident, so it is necessary to monitor structure health of large buildings. Deformation monitoring is one of the most important means to monitor structure health. Compared to other methods, radar measurement has many advantages by using microwave and corner reflector. Microwave is less susceptible to environment and corner reflector is much cheaper than GPS, so radar measuring is with great potential in the area of structure health monitoring. FMCW is an important method in radar measuring, however, assume to use it in actual measuring, much research should be done on its accuracy. Affection of VCO’s inherent nonlinearity and parasitic amplitude modulation and Echo’s multipath echoes, environmental noise and direct coupling between antennas on FMCW Radar System are pointed out.Firstly, VCO’s working principle and its nonlinear effects on radar system is analyzed and the various types of linear calibration method is reviewed and compared. According to the actual conditions, digital open- loop correction method for correcting linear VCO and corresponding results is proposed. At the same time, because of the effects of parasitic amplitude modulation which is modulated by VCO in FM, beat signal is mixed with a fixed amplitude signal which has the same frequency with the modulation signal, invariable frequency and amplitude are the characteristics of parasitic amplitude modulation signal. Fourth-order band-pass filter is designed to filter it out, filter design methods is elaborated and final physical map is presented.Secondly, a mathematical model is established to analyze the effects of multipath echoes, environmental noise and direct coupling between antennas on radar system.Finally, an actual radar system is introduced which uses radar transceiver IVS-163 as a front-end module and USB-6251 data acquisition card as a data transmission module with the host computer, PC software is programmed by Lab VIEW to control the entire radar system to beat signal spectrum estimation. During actual experiment, in order to improve measurement accuracy, zeros spectral difference frequency signal is used to refine and improve the accuracy of frequency measurement, thereby improving the accuracy of the distance measurement. The final results showed that, the measurement accuracy can achieve millimeter within 3m and about 1 decimeter near 15 m.