Yearly variation of the rain attenuation statistics in Ka and Ku band satellite communications links

Long-term rain attenuation statistics of the Ka and Ku band satellite signals obtained from 1988 to 2006 at Osaka Electro-Communication University in Neyagawa, Osaka, are investigated for the yearly variation of their attenuation characteristics. The ratio of Ka-band to Ku-band attenuation indicates yearly fluctuations of more than ±10% around the mean value in their equi-probability relationship, being considerably larger than the frequency scaling model of the ITUR predictions. This study reveals that the deviation from the ITU-R frequency scaling model is primarily caused by the difference of raindrop size distribution (DSD) between the stationary fronts that give rise to the rainfall in the East Asian rainy season (Tsuyu or Baiu) or Autumn rain (Akisame) unique to Japanese climate. Also, the occurrence rate of summertime shower and typhoon is found to affect DSD. In addition, the deviation rate of the attenuation ratio from the ITU-R predictions is found to be correlated with the yearly time percentages of stationary fronts and typhoon. For practical satellite communications links, yearly and long-term time percentages and the rain margins required for specific time percentages are then presented to the CS rain attenuation actually measured and estimated by the frequency scaling method.