Signal current probability distribution for optical heterodyne receivers in the turbulent atmosphere 1: Theory

Approximate expressions are derived for the probability density functions of the i.f. signal magnitudes from optical heterodyne detection systems operating in the presence of clear air turbulence. The effects of lognormal amplitude fluctuations and Gaussian phase perturbations, in addition to local oscillator shot noise, are considered for both passive receivers and those employing active tilt-tracking systems to eliminate angle-of-arrival fluctuations. In Part 2, experimental results are presented that verify the density functions developed here.