High throughput satellite communication systems, need to utilize less congested high frequency bands, such as Kaand Q-bands and above with a large available radio channel bandwidth. However, the disadvantage of radio wave propagation at these frequencies is the increased attenuation and impairment caused from tropospheric phenomena, in particular by rainfall. Site diversity is an efficient technique to mitigate the attenuation due to rain. In this paper, we present the performance evaluation of the large-scale dual site diversity system based on the long-term beacon signal measurement of geosynchronous Alphasat satellite at 19.701 GHz between the Earth stations in Ljubljana and Budapest. The statistical analysis of one-year measurement of rain attenuation of the site diversity system is presented. The results show that the mitigation of the rain attenuation in site diversity is significant.