Abstract:
Rain induced depolarization due to distorted rain drops may be a serious problem
to satellite communication at short wavelengths when dual - polarized signals are
employed. This study investigates the effects of rain induced depolarization on circularly
polarized millimeter and centimeter wave propagation in a tropical location (Nigeria).
Propagation along the Earth-space path is considered. Cross-polarization discrimination
(XPD) and copolar attenuation (CPA) are calculated for an effective raindrop canting
angle of 10° with standard deviation of 19° and for varying elevation angles. Three
tropical rain types classified as widespread, shower and thunderstorm are assumed. The
frequency range of the study covers the band 4-100GHz. The study presents results for
the variation of XPD with frequency, path length to the rain region, XPD as a function of
fade depths (CPA) and so on. The study found that for convective rain types (shower and
thunderstorm) cross polarization discrimination becomes very poor as elevation angle
decreases and frequency and rain rate increases. For instance, as elevation angle becomes
low (e.g. 23°), because the path length to the rain region becomes longer, XPD falls
rapidly with increasing rain rate. Copolar attenuation on the other hand increases with
increasing rain rate and frequency. The study also found that depolarization of circularly
polarized waves is more severe when signal transmission is through convective rain type.
