Phase Noise in FMCW Radar Systems

Phase noise is one of the fundamental performance parameters in modern radar, communication, spectroscopic, and metrological systems. In this paper, a phase noise theory has been developed for FMCW radar systems. A new design equation has been derived to specify the maximum bound on the allowable source phase noise level in radar systems. The nonlinear phase noise decorrelation function due to coherent mixing has been analyzed for propagation delays less than the coherence time of the reference oscillator, and the spectral broadening of target responses has been discussed for delay times greater than the coherence time. The effects of the subsystems in the transceiver chain are presented and a new model of phase noise in ADCs is discussed. Phase noise modeling techniques are presented, followed by a comparison of a PLL frequency synthesizer with a low-noise frequency synthesizer to demonstrate the reduction of phase noise sidebands for improved detection and tracking performance. Practical measurements from two millimeter wave FMCW radar systems utilizing the two frequency synthesizers have been presented to validate the developed theory.