Study of measurements and prediction models for signal attenuation in vegetation media at microwave frequencies

Abstract

The effects of vegetation media on the planning and design of radio links at microwave and millimeter wave frequencies are considerable and must be accounted for by radio system operators and users. This paper presents a study of propagation models for the excess attenuation of signals caused by such media whose mathematical descriptions have been optimized using measured data. This paper shows that one of the models which expresses the attenuation as a function of frequency and depth of vegetation gives close predictions for the two broad generic cases of trees 'in-leaf and 'out-of leaf . Measurements have been made to determine the extent of attenuation of millimeter-wave signals when propagated through vegetation. Methods for predicting such attenuation exist, but are either deterministic in form or therefore complex to implement or are completely empirical and take no account of measurement geometry. A new semi-empirical model is presented here which is based on measurements of vegetation attenuation presented previously, and has some account of the measurement geometry. This model is compared with measured data and is shown to give considerably better agreement.