Dual-polarized operation of satellite communications channels allows for an efficient use of the radio spectrum. A method for evaluating the availability of Ku- and Ka-band dual-polarized digital systems is described. It is based on long-term measurements of slant-path attenuation and depolarization caused by the troposphere and of their joint occurrence. The additional degradation of dual-polarized system availability performance with respect to single polarization operation is assessed, and its dependence on major link and system parameters is highlighted. It appears that satellite links characterized by high-frequency, low elevation angle, circular polarization, and high-level modulation schemes are particularly affected by the depolarization-induced interference. In that case, doubling their capacity by dual-polarization frequency reuse reduces dramatically their availability, assuming a fixed link margin, or alternatively requires prohibitive link margins to meet a given availability objective.

An original and general method is proposed to predict the impact of electromagnetic effects due to the environment on the error performance of microwave communications systems. The method is based on the concept of a process-oriented model which consists of a simplified representation of the physical phenomenon responsible for transmission impairments and simulates its influence on the signals received by any given communications link. The method yields a thorough characterization of the system impairments in both the time domain, by calculating the fluctuations of the received signal during the evolution of the physical process, and the frequency domain, by inferring the communication channel transfer function from the frequency dependence of the received waveform. In addition, by introducing the simulated channel transfer function as a filter in a communications system simulation software, the method evaluates the degradation induced in the system performance. Three applications as different as scintillation due to turbulence in clouds, depolarization by rain and ice crystals, and interference in the presence of diffraction on obstacles demonstrate the ability of the method to deal with actual radio-communications system impairments.