A Study on Frequency Scaling of Rain Attenuation Using Simultaneous Measurements of Ka-Band and Ku-Band Satellite Beacon Signals

Rain attenuation characteristics were investigated by using simultaneous observation data of rain attenuation conducted on the same propagation path using Ka-band and Ku-band beacon signals of Superbird-B3 at NTT Yokosuka Research and Development Center (Yokosuka City) from June to December 2023. The ratio of rain attenuation in both frequency bands shows slightly larger values than the ITU-R frequency scaling method, suggesting that the ration is underestimated by the ITU-R predictions. The deviation in the ratio can be explained almost within the range indicated by the theoretical values of three typical kinds of raindrop size distribution: drizzle type (Jd type), standard type (MP type), and thunderstorm type (Jt type). Compared with these theoretical values, the ratio is found to be influenced by the Jd type when stationary fronts pass through, while it is influenced by the Jt type on the south of the stationary fronts. Also, it is influenced by the Jt type in convective rainfall such as summer time showers. As a result, the instantaneous values of Ka-band rain attenuation can be estimated from those of Ku-band rain attenuation with an accuracy of about 15% or less considering the raindrop size distribution. On the other hand, the two-year rain attenuation statistics were presented for BS and JCSAT-5A signal observations from April 2022 to March 2024. Then, the frequency scaling methods from Ku to Ka band are discussed at Neyagawa, Yokosuka, and Matsuyama stations. At Neyagawa and Yokosuka stations, the inferred Ka-band attenuation statistics are found to be larger than the ITU-R predictions using the 0.01% rainfall rate. At Matsuyama station, however, the rain attenuation statistics are slightly smaller the ITU-R predictions.