| dc.description.abstract | Abstract:
The rapid growth in demand for additional communication capacity has put pressure on engineers to develop microwave systems operating at higher frequencies. Many people tend to choice the Ka-band (26-40 GHz) for the applications. It turns out, however, that frequencies above 10 GHz attenuation caused by atmospheric particles can reduce the reliability and performance of radar and space communication links. Such particles include oxygen, ice crystals, rain ,fog, and snow. Prediction of the effect of these precipitates on the performance of a system becomes important. In this study, we will discussed the prediction of attenuation of an EM wave propagating through rain drops.
The prediction of attenuation due to rain is considered the EM wave propagating through rain drops, the energy of the EMW will be absorbed and scattered by rain drops, then the raindrop-size distribution (DSD) is the most part in the prediction of attenuation due to rain. Many raindrop-size distribution have been reported. Exponential、Gamma 、Weibull、Lognormal distribution have been use to be the raindrop-size model. Because use the suitable raindrop-size distribution model, we can calculate the rain attenuation more accurately. In this study, we analysis the raindrop-size distribution in Chung-li, then we find the raindrop-size distribution in Chung-li follow the Gamma distribution; then a Gamma raindrop-size distribution is proposed by fitting the measurements of rainfall observed using a distrometer in Chung-li, the three parameter of raindrop-size is μ=0.67364‧R0.19476;σ=0.23637‧R0.29347;N0=829.63‧R0.30689. Then we use Gamma raindrop-size distribution model to predict the rain attenuation due to rain. We will assume that rain drops are spherical and the scattering mechiasm follows the Mie scattering theory .
In the passing research of rain attenuation prediction, Crane. R. K. proposed the “Global (Crane) Attenuation Model (1978)”and ITU proposed the “ITU-R P838”rain attenuation prediction methods, finally, we comparison of the rain attenuation measurements result using our “Ka band (28GHz) terrestrial link propagation system” and the prediction result from Chung-li raindrop-size distribution model and and Crane Global (Crane) Attenuation Model and ITU-R 838 rain attenuation prediction methods, then we find the prediction from our raindrop-size distribution have very good prediction, but Crane model have higher prediction and ITU-R model have lower prediction. | en_US |