| Due to the advantages of large time-bandwidth product, high resolution, no distance blind area, strong anti-interference ability, low transmission power and easy integration, FMCW(frequency modulation continuous wave) radar has broad application prospects in precise guidance, automotive anti-collision, building, liquid/material level measurement. Measuring principle and basic hardware of FMCW is becoming complete, but measuring precision and real-time performance of practical application still needs to improve. Based on the research of ranging theory of FMCW radar and the research and processing of short-range distance heterodyne frequency signal, using the radar sensor IVS-179 and TMS320F28335, FMCW radar ranging system was designed, and key technology of measuring accuracy was studied according to experiment.Working mechanism and sawtooth wave ranging principle of FMCW radar was studied, and frequency spectrum leakage and inherent resolution of the heterodyne frequency signal was analyzed. Then, hardware and software design of the FMCW ranging system was finished. A digital programmable waveform generator was designed in view of waveform voltage correcting FM linearity. Modulation leakage and distance characteristics of heterodyne frequency signal of FMCW radar was analyzed, and MFB high-pass filter, adaptive programmable amplifier circuit and Sallen-Key low-pass filter was designed respectively to solve leakage, signal strength, and high frequency interference.Pros and cons of existing frequency discrimination algorithm was presented. The implementation principle and calculation procedure of WIN_FFT_CTA algorithm was introduced. Then, the idel accuracy of measurement was acquired by simulation, the feasibility of using initial phase to improve measurement precision are analyzed. Finally, frequency discrimination algorithm in DSP was achieved using C language, time of single algorithm computation is 58.5ms.Experiment platform of ranging system was builded, FM linearity was indirectly expressed as distance flatness, and the FM linearity is improved about 16 times, using the short-time WIN_FFT_CTA algorithm estimate the instantaneous frequency of heterodyne frequency signal approximatly. Distance was demarcated by stepper incremental distance adjustment and linear fitting. Using the frequency discrimination algorithm, ranging accuracy is greatly increased in the distance measurement experiments, range estimation precision is 2mm using the frequency, 0.15 mm using initial phase. |
PDF Full Text Request