The influence of the interaction effects of the transmitting and receiving antennas of a millimeter-range radar, as well as the direct transmission of the transmitter signal to the receiver input via the internal circuits of the microwave chip on the level of the decorrelated phase noise is under consideration. It is shown that for a certain amount of interaction between the antennas, the delay time of signal propagation along the paths of additional reception, the receiver noise factor and the level of phase noise of the carrier frequency of the transmitter at the detuning frequency equal to the frequency of the useful signal, the output noise power of the receiver converter by the additional receiving channel and the receiver’s own noise become comparable. Due to the additional noise reception channel, the signal-to-noise ratio decreases and the range of the radar action decreases as well. The calculation uses data for the noise factor of the receiver and the spectral density of the phase noise of the synthesizer of the AWR1243 millimeter-wave transceiver chip from Texas Instruments in the frequency range from 77 till 81 GHz. The effect of a dielectric antenna shelter on the coupling between the transmitting and receiving antennas, and on the spectral noise power density at the receiver input, is considered. The dependences of the spectral density of the decorrelated phase noise due to additional communication channels in comparison with the receiver’s own noise are shown.