Study of effects of rocky terrain on microwave line of sight link at C, J, X and Ku bands

Abstract

The rocks are formed during the process of formation of earthpsilas crust. Rocks found on the earth surface are mainly three types, namely, igneous, metamorphic and sedimentary rocks. The microwave link operating over the rocky surface results in the fading of the received signal. The effect of rocky terrain on microwave link is manifested in the fading of the signal which takes place due to the destructive interference between the signals reaching the receiver by direct path and that of reflected from the rocky terrain. The destructive interference depends mainly on two factors namely, phase difference between the direct and the reflected rays and the inherent electrical properties of the rock considered. The electrical properties like dielectric constant, reflection coefficient vary with types of rocks, which in turn result in the variation of emission and scattering behavior. Apart from these properties the surface roughness plays a great role in the received power, as the power received via surface is due to the diffused scattering from the rough surface. The calculation of exact surface roughness profile must be needed for study of the link performance. In this study a microwave line of sight is operated over rock surface using pyramidal horns as transmitting and receiving antenna after clearance of fresnel zone. After characterizations of antenna at different microwave frequencies, the heights of the antennas are adjusted to clear the diffraction zone, hence we are sure that there are only reflections coming from the terrain. The absorbing material is used to differentiate between direct received power and reflections coming from the terrain. Therefore, the factors, which are responsible for fading of a signal, have to be properly studied. The diversity aspects are also to be considered as remedial measures to avoid fading of the signal. In this paper, the effects of rocks on the microwave radio link are presented for different frequencies, i.e. 5.85 GHz in CJ band, 10.3 GHz in X band and 12.85 GHz in Ku band for different antenna heights and for vertical and horizontal polarizations. The results of this study help the designers of microwave links with frequency, space, polarization and combined diversity techniques.