Mutual interference in the frequency modulated continuous wave (FMCW) radar is studied, and the influence of the FMCW interference on the beat frequency is analyzed. An analytical expression for the victim radar received signal spectrum is derived. Different interference scenarios are investigated by means of interference impact on the range-Doppler profile. It is shown that coherent interference concentrates within multiple range cells while non-coherent interference spreads the interference power over the whole range-Doppler plane.