Plane wave spectrum treatment of microwave scattering by hydrometeors on an Earth-satellite link

For satellites operating at frequencies above 10 GHz, the effects of propagation through atmospheric hydrometeors are of major importance. In particular, the hydrometeors attenuate, cross polarize and scatter signals causing respectively: a loss in signal level, a decrease in the efficiency of dual polarized channels and station to station interference. For large Earth station antennas operating at high frequencies, the near or Fresnel region of the antenna can extend several kilometers from the antenna and consequently, during disturbed weather, a significant proportion of the hydrometeors affecting propagation are in the near or Fresnel region of the antenna. Previous treatment of propagation through hydrometeors in the Fresnel region of an antenna has proved unsatisfactory and the plane wave spectrum technique was used to accurately characterize antenna scatterer interaction in both the near and far fields of an antenna. The Van de Hulst refractive formula for the coherent propagation and the basis of the radiative transfer equation for the incoherent scattering are derived.