Modelling of the re-radiation functions of single trees based on wideband measurements at L-band

In urban and rural areas, radiowave propagation is generally dominated by diffraction loss and reflections from buildings and trees. In the case of land mobile systems, trees, singly or in a group, are usually present in the environment surrounding the receiver. An important part of the modelling process is aimed at identifying the individual contributions of the elements giving rise to the scattered signal. Studies around the 2 GHz band were performed on a mature deciduous tree in order to characterise the complex propagation modes emanating from a single tree. Measurement campaigns were conducted in autumn/winter and spring/summer on the same tree. A measurement system has been developed for short-range outdoor radio channels incorporating a vector network analyser (VNA), configured for swept frequency measurements. The results of an investigation based on the measured complex impulse response (CIR) at various positions around the tree for both co-polar and cross-polar received signal components, are presented. A discrete mathematical model is used to compute RMS delay spread of the power delay profiles (PDP) for both foliated and de-foliated states of the tree. Seasonal variations and the effects of leaf movement on the channel characteristics caused by wind, are also discussed.