Method for testing prestress of foundation pit anchor cable based on millimeter wave radar

The invention discloses a method for testing the prestress of a foundation pit anchor cable based on a millimeter wave radar, and the method comprises the steps: continuously transmitting electromagnetic waves to the anchor cable based on a radar detector, so as to obtain a corresponding phase change, and further calculating the vibration change displacement of the anchor cable; then, an anchor cable vibration frequency time history curve is obtained through software analysis, discrete Fourier transform is conducted on the anchor cable vibration frequency time history curve, a time domain signal is converted into a frequency domain signal, and the anchor cable prestress is calculated. According to the scheme, non-contact measurement is adopted, the prestress of a plurality of anchor cables can be measured at the same time, the principle is reliable, and the working efficiency is high; the millimeter wave radar can penetrate through the sheath to directly test a strong anchor cable reflection signal, the relia