FM continuous wave radar refers to a continuous wave radar whose transmitting frequency is modulated by a specific signal. The principle of frequency modulated continuous wave (FMCW) radar is to send a continuous signal with a certain bandwidth and linear change in frequency, and then perform fast Fourier transform on the received continuous signal. The time difference between the two signals is calculated by the frequency difference between the sending and receiving signals. Finally, like the pulse wave radar level meter, the corresponding distance value is obtained from the time difference. FMCW radar can obtain very high accuracy, and its accuracy mainly depends on the linearity and temperature drift of the voltage controlled oscillator.