Phase Noise
Phase noise refers to noise in a carrier signal due to phase and frequency modulation in the signal. Phase noise is normally very close to the carrier and is measured in decibels relative to the carrier frequency (dBc).
Phase noise is expressed as a function of power spectral density and frequency. In a 1 Hz bandwidth, phase noise is given by
= 10log[0.5(S Φ(ƒ))]Φ
where S Φ(ƒ) is the spectral density of phase fluctuations.