Why is phase noise measurement important?
Phase noise determines the performance of many systems such as the CW radar systems used to detect moving targets. The phase noise reflected by stationary objects competes with the Doppler shifted carrier from a moving target. This competition generally sets the lowest velocity target that may be identified. In chirped-FM radar such as weather radar, the reflected signal is compared to currently broadcast signal. The difference in frequency between the reflected signal and the currently transmitted carrier is proportional to the distance from a reflecting object such as a cloud. The Allan deviation of the reference oscillator corresponding to the round trip time to the reflecting object and back quantifies the reference oscillator’s contribution to the noise or jitter of the radar. For precision oscillators, manufacturers publish specifications in both the frequency domain (phase noise) and in the time domain (Allan deviation). For application-specific oscillators, manufacturers may on
