Depolarization due to precipitation in satellite communications

The theory on cross-polarization induced by rain on an electromagnetic wave is extended to include antenna effects. Of interest are the communication bands 4-6 and 12-14 GHz. In satellite-earth propagation links designed for frequency reuse using two orthogonal polarizations in order to double the channel capacity, the generation of cross-polarization decreases the isolation between the orthogonal channels. The analysis covers: (1) the finite clear-weather isolations and/or the co- and cross-polarization patterns of the transmitter and receiver antennas, (2) misalignment between the transmitter and receiver polarization vectors and/or Faraday rotation for linear polarization, and (3) polarization angle of a signal received off-axis from the transmitter pattern. Parameter plots illustrating all these effects at 4, 6, and 11 GHz, and for certain elevation angles, are displayed for both linear and circular polarizations. Other causes of cross-polarization considered are due to interfering satellites and multipath. Compensation methods to eliminate the cross-polarization components are discussed.