Phase and frequency stability for synthetic aperture LADAR

We analyze the phase and frequency stability requirements of the optical phase reference in a synthetic aperture LADAR imager. There are three distinct frequency regions: (a) "low" frequencies, below the characteristic frequency of the coherent synthetic aperture; (b) "mid" frequencies, up to four times the characteristic frequency of the coherent synthetic aperture; and (c) "high" frequencies, up to and beyond the pulse repetition frequency. The low-frequency requirement is driven by the allowable quadratic phase error, related to the resolution of the impulse response. Mid- and high-frequency requirements are driven by the allowable peak and integrated sidelobe levels. We estimate the upper bound and average PSDs required of the reference oscillator, parametrized by imaging geometry variables such as range, wavelength and synthetic resolution.