Effect of Ice-Induced Cross-Polarization on Digital Earth- Space Links

Among the techniques proposed to increase the capacity of the allocated frequency bands, reuse of the same channel twice with orthogonal polarizations seems to be very promising. However, imperfect isolation between the two orthogonal channels, arising, for example, from nonspherical scatterers encountered by the transmitted waves during propagation, is likely to limit the possibilities of this frequency reuse technique. While rain-induced cross-polarization is relatively well understood, the impact of cross-polarization coupling due to ice crystals on communication systems has to be thoroughly investigated. In this paper a statistical analysis of depolarization events observed at 20 GHz from the linearly polarized beacon of ATS-6 is carried out. It shows that ice depolarization events occur as frequently and are as significant as rain depolarization events, and also that ice crystals are typically canted within
\pm10\deg
of the vertical. From the results obtained, the effect of ice cross-polarization on a dual-polarized microwave link utilizing
M
-ary PSK transmission is investigated. These results point out the necessity of implementing cross-polarization cancellation devices.