A method and apparatus for determining a frequency of an echo signal obtained by a radar system is disclosed. The echo signal in response to a source signal of the radar system is received at a receiver. A harmonic oscillator generates a harmonic component signal, and a multiplier multiplies the echo signal with the harmonic component signal to obtain a combined signal. A Fast Fourier Transform (FFT) is performed on the combined signal to obtain a peak in a frequency space, wherein a central frequency of a frequency bin in the frequency space is shifted with respect to the frequency of the echo signal by the harmonic component signal. The frequency of the echo signal is determined from the shifted central frequency.