This work presents the design and measurement of a fractional-N phase locked loop (Frac-N PLL) based chirp generator for frequency modulated continuous wave (FMCW) radars. Various design aspects such as phase noise (PN), chirp slope, chirp linearity and chirp counter frequency are investigated by modelling and measurement results. Ranging measurements from an FMCW radar test chip fabricated on an IBM7WL BiCMOS 0.18 pm technology are in good agreement with simulations. A ranging precision of 5 mm is achieved in lab conditions while a root mean squared (RMS) positioning error of 10 cm is achieved in a practical indoor tracking scenario with a relatively large track (8 m × 12 m) using only 4 base stations (BSs). With such accuracy, the developed local positioning system (LPS) competes with more sophisticated multiple-input-multiple-output (MIMO) based FMCW radar LPSs incorporating a larger number of BSs.