SUMMARYThe unavailability due to rain of VSAT star networks operating on Ku and Ka bands in Brazil is analysed in this paper. A large number of simulations performed over the Earth-space links resulting from combinations of four (real and hypothetical) satellites with six Brazilian Earth stations provide a good characterization of the rain unavailability in tropical and equatorial regions subject to heavy rainfall and thunderstorms. The simulations also compare the influence on the estimated unavailability of the use of two different ITU-R rain attenuation models and two values (calculated and measured) for the rainfall rate exceeded during 10 À2 % of the time, the climatic parameter in the models, in addition to the link polarization employed. The results obtained point to VSAT star networks as a practical solution to provide telecommunications services to remote communities.
A simulation model of multipath propagation will be used to characterize the relationship between the cross‐polarization discrimination and the co‐polar attenuation in frequency‐reuse line‐of‐sight microwave links. The behavior of several links described in the literature will then be simulated, and the results will be compared with the corresponding measurements, to test the prediction capability of the model. A reasonable agreement between the corresponding results will be displayed. Further, it will also be shown that the cross‐polar phase patterns of the antennas could significantly affect the behavior of the cross‐polarization discrimination.
&USTRACTRayleigh fading caused by tropospheric ducts was observed on seve_ ral lineof-sight microwave links in different regions of Brazil. The available prediction models were not adequate. A good correlation with measurements was only possible with the inclusion of parameters associated. with shadow-region reception conditions caused by ducts.
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