Comparison of Millimeter-Wave (35 GHz) Attenuation in Foliage Depth by Various Empirical Models with Observed Attenuation of Wave Prevailing in Desert Region of India

When a signal scatters, traditional theory says that scattered field components are independent of each other. But scattering phenomenon is different in the case of foliage which consists of bunch of leaves and branches. In coherent scattering, scattered field components scatter in such a manner that there are some scattered components which are in same phase. These in-phase components combine back to give strength for propagating signal. Rate of attenuation decreases in foliage depth due to coherent scattering. By computing difference between actual and theoretical attenuations, it is concluded that 35.6% in autumn, 23.33% in spring, 25.88% in winter, and 18.63% in summer of signal are coherently scattered. It signifies that above percent of signal reconstructs due to scattering in-phase components. During autumn, signal attenuation is minimal, and the coherency of scattered elements tends to be the highest. However, water molecules in the spring and fog in the winter can increase attenuation. Therefore, for effective line-of-sight communication through foliage using millimeter waves, maintaining coherency becomes crucial. Attenuation rate of 0.22, 0.179, 0.211, and 0.210 dBm/feet is found for initial five trees for autumn, spring, winter, and summer seasons, respectively. But as foliage depth increases, rate of attenuation decreases to average 0.11, 0.13, 0.121, and 0.135 dBm/feet for twelve canopies for autumn, spring, winter, and summer seasons, respectively. So, it can be said that the rate of attenuation decreases with an increase in foliage depth. By comparing observed values with predefined empirical models for foliage depth attenuation, it is drawn that the observed curve is closer to the ITU-R model up to 26.6 m, and then, it tilts toward Weissberger model for autumn, summer, and winter seasons. Attenuation in spring season is evaluated to be specifically higher than any of the empirical model for initial foliage depth of 60 m, and then, it approaches to ITU-R model. Curve behavior of winter and summer seasons is same.