The state-of-the-art FMCW Chirp synthesizer PLLs published in the last decade report chirp nonlinearity using an RMS frequency error metric, which is of no importance for radar system modeling. This article develops a rigorous methodology to accurately measure frequency ramp nonlinearity and phase error of synthesized chirp signals commonly used in frequency-modulated continuous-wave (FMCW) radar applications. An approach to measure frequency linearity of the chirp is developed to 1) overcome contemporary VSA instrumentation and software limitations for FM filter bandwidth ffm,BW > 10 MHz when the FM slope trace may be unstable and misleading, and 2) to overcome the inherent instrumentation noise. PLL synthesizer phase noise and error are calculated from the difference of the ideal ramp and the measured FM data with an innovative phase noise averaging technique to remove instrument noise. This article shows that the frequency domain representation of chirp frequency error and/or phase error is mandatory to model the impact of chirp nonlinearity on radar systems.