This work presents an approach for estimating the effect of the fractional-N phase locked loop (Frac-N PLL) phase noise profile on frequency modulated continuous wave (FMCW) radar precision. Unlike previous approaches, the proposed modelling method takes the actual shape of the phase noise profile into account leading to insights on the main regions dominating the precision. Estimates from the proposed model are in very good agreement with statistical simulations and measurement results from an FMCW radar test chip fabricated on an IBM7WL BiCMOS 0.18 μm technology. At 5.8 GHz center frequency, a close-in phase noise of -75 dBc/Hz at 1 kHz offset is measured. A root mean squared (RMS) chirp nonlinearity error of 14.6 kHz and a ranging precision of 0.52 cm are achieved which competes with state-of-the-art FMCW secondary radars.