Investigation of Depolarization and Cross Polarization over Ku-band Satellite Links in a Guinea Savanna Location, Nigeria

Abstract

In communication systems engineering, designers tend to optimize the channel capacity of radio links through frequency re-use by deploying dual independent orthogonally polarized channels in the same frequency band. Such frequency re-use techniques via linear or circular polarization are severely impaired by the interference of cross-polarized signals, because the energy from one polarization is transferred to the other orthogonal region. Depolarization effects on satellite links are described in terms of cross polar discrimination (XPD). The parameters mainly responsible for depolarization due to scattering by oblate spheroid raindrops at Ku-band can be estimated from satellite beacon footprint data. In this paper, data obtained from Ku-band, EUTELSALAT (W4/W7) at a frequency of 12.245 GHZ and elevation angle of 036° E over Jos, Nigeria (9.9565° N, 8.8583° E, 1258 m) were analyzed. One minute rain rate obtained from rapid response rain gauge was also analyzed alongside the beacon measurements. Consequently, the aforementioned data were applied to the ITU-R procedure in recommendations 618-12 to estimate XPD due to rain on earth satellite path over the study location. The results show positive values of XPD, the threshold of rain rate of 27 mm/h, while the threshold for co-polar attenuation was found to be 5.6 dB. Also, negative XPD values of about -120 dB obtained indicated that very high incidences of interference and cross-talks could occur in the region; and this could inhibit frequency re-use in the Guinea Savanna region of Nigeria. The overall results obtained provided useful models and thresholds values for radio communication planning in the region.