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Performance of FMCW generators based on DPLLs are significantly affected by the presence of spurs. The latter may originate from the inherent operation of the DPLL itself, when operated in Fractional-N mode, or by external aggressors via coupling paths. Moreover, non-linearities of the loop can result in a worsening of the spur level thus in a degradation of the generated frequency modulation. This paper provides an insight on spurs impact in PLL-based chirp generators for radar sensors. Three different scenarios are taken into account: fractional spurs arising from non linearities, spurs coupling to the output of the DPLL and coupling of the digital activity of the divider to the DCO. The analysis is performed by means of a time-domain model of the FMCW Radar transceiver for target detection, and the effect on the range FFT and on Doppler shift of the base-band signal is presented.