a frequency modulated continuous wave radar signal is transmitted to a tat and the signal reflected from the target is compared with a sample of the continuous wave transmitter to produce a difference frequency signal . the difference frequency signal is band - pass amplified , wide - band limited , and processed by two frequency discriminators displaced from each other in the frequency domain , but both within the frequency band of the limiter and band pass amplifier . detectors , integrators , and thresholding circuits determine , with suitable false alarm rates , in which half of which discriminator the difference frequency signal is concentrated .