Fundamental Limitations of Crystal Oscillator Tolerances on FMCW Radar Accuracy

Crystal oscillators (XOs) are widely used in fractional-N phase locked loops (Frac-N PLLs) as reference frequency sources due to their good phase noise performance. However, these XOs have manufacturing tolerances in the range of few tens of parts per million (ppm). When a Frac-N PLL is used in frequency modulated continuous wave (FMCW) radar applications, the XO accuracy affects the frequency and timing accuracies of the radar chirps and so it directly affects the distance measurement accuracy. In this work, the fundamental limits of XO tolerance on distance measurement accuracy of FMCW radars are discussed and modelled. Moreover, an FMCW radar system hardware prototype is developed. Measurement results are in good agreement with the expectations of the simulation model.