Antenna resolution as limited by atmospheric turbulence

Spatial variations of the index of refraction of the atmosphere introduce fluctuations in the phase and amplitude of a wave propagating through it. The effect of these fluctuations on the resolution capability of microwave antennas is discussed in this paper. The measure of resolution used in the calculations is the beamwidth, which is defined as the square root of the second moment about the mean of the normalized antenna pattern. This measure simplifies the calculations greatly and results in a simple expression for the beam broadening due to the variation of the refractive index. This broadening is dependent on the distance to the target, the scale of the turbulence, and the variance of the refractive index and is relatively insensitive to the shape of the spatial correlation function of the refractive index. Measurements by others of the nature of the refractive index spatial variation are then used to obtain numerical estimates of the ultimate resolution capability of a microwave antenna as limited by atmospheric turbulence.