Slant-Path Rain Attenuation Statistics over Nigeria
Slant path attenuation of microwaves due to rainfall intensities exceeding 0.01 and 0.001per cent of average year have been computed for five different geographical zones in Nigeria, using relevant ITU-R recommendations and global rain rate data. The resulting charts can be used for preliminary estimates of maximum rain-induced attenuation of microwaves expected on earth-satellite paths of elevation angles 20-90
degrees in Nigeria, for the L, C, ka and ku frequency bands, which are presently used by the Nigerian communication satellites. The study shows that attenuation is higher for western, southern, or lower altitude stations. Also attenuation of horizontally polarized waves exceed that of vertical polarization by increasing margins at higher frequencies, which makes vertical polarization more preferable at higher microwave frequencies. Thus, the emerging LEO and MEO satellite systems that will operate on frequencies as high as 40 GHz may be practically restricted to vertical polarization due to rain attenuation. Based on the curves, rainfall attenuation in Nigeria may be negligible on slant microwave links at L-band and lower frequencies, no matter the elevation angle; but may cause significant propagation problems at C-band and higher frequencies,
especially at low elevation angles.
Key words: Microwave attenuation, polarization, radio propagation, frequency band, rainfall rate .