Residual phase noise and transmit/receive isolation in a submillimeter-wave FMCW radar

Detection sensitivity of a frequency-modulated continuous-wave (FMCW) radar can be limited by transmitter noise leaking into the receiver. For submillimeter-wave radars relying on high harmonic frequency-multiplication factors N>>1, phase noise typically dominates this leakage because it is amplified by 20log(N). A feed-forward phase noise cancellation circuit can suppress the effect of this leakage. Here we investigate quantitatively how effective this cancellation can be, finding that it is limited by additive residual phase noise in the harmonic generation chain. These results drive the transmit/receive isolation requirement in submillimeter-wave radars.