As the operating frequencies of communications systems move higher into the millimeter wave region, the effects of multiple scattering in precipitation media become more significant. In this paper, general formulations are presented for single, first‐order multiple, and complete multiple scattering. Included specifically are distributions of particle size, shape, and orientation angle, as well as variation in the medium density along the direction of wave propagation. Calculations are performed for rain. It is shown that the effects of higher‐order scattering are not noticeable in either attenuation or channel isolation on a dual‐polarized system until frequencies of about 30 GHz are reached. The complete multiple‐scattering formulation presented gives accurate results at high millimeter wave frequencies as well as including realistic medium parameter distributions. Furthermore, it is numerically efficient.

This paper summarizes measurements of ice depolarization made using a unique facility consisting of a dual‐site (7.3‐km site spacing), dual‐circularly polarized, low‐elevation angle (10.7°) receiving system for the SIRIO 11.6‐GHz beacon. Significant depolarization (cross‐polar discrimination as low as 10 dB) in the absence of attenuation occurred relatively frequently. However, the impact of the ice on the cross‐polar discrimination statistics for a 6‐month time period was small.

The Dyson equation and the two‐frequency Bethe‐Salpeter equation for vector‐valued electromagnetic waves in the presence of a random distribution of absorptive discrete scatterers with pair correlations are derived on the basis of the Twersky multiple scattering formalism. These equations are subsequently “scalarized” in the case of a tenuous scatterer distribution and within the framework of the Rayleigh‐Debye condition. A systematic transition is then made to a two‐frequency radiative transfer equation via a phase‐space approach. The main strength of the radiative transfer theory expounded here stems from the fact that it is applicable under conditions of large‐angle scattering, statistical inhomogeneities and statistical anisotropies. It accounts, also, for a variable scatterer density, absorption, and frequency offsets.

In this paper, theoretical methods are presented for calculating the depolarization of ice clouds. Rayleigh scattering from single particles is used. A general theory is introduced that includes distributions of ice particle shapes and orientation angles for both single and multiple scattering. It is shown that the more accurate multiple scattering formulation yields cross‐polar discrimination values significantly worse than those for single scattering over the 10‐ to 30‐GHz band for high ice content. Comparisons are made to measurements using the SIRIO satellite.

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