Measurement of propagation loss in trees at SHF frequencies

• Main Author: Adegoke, Adesoye Sikiru
• Other Authors: Siddle, David; Warrington, Michael
• Published: University of Leicester 2015
• Subjects: 621.384
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.634392

Measurements on single trees, group of trees and lines of trees have been undertaken at microwave frequencies (3.2-3.9 GHz and 4.9-5.9 GHz) in order to investigate the influence of trees on radio waves. Several factors that are thought to be influencing excess loss estimation in trees were considered, among which are canopy thickness, leaf density, operating frequency, states of foliation and antenna geometry. Efforts were made to carry out repeat experiments at different periods of the year (autumn, winter, spring and summer) in order to include seasonal effects of trees on radio waves in the investigation. Results show that attenuation as high as 30 dB in excess of free space were recorded across single isolated trees. For the woodland (group of trees) experiment, an overall increase in excess attenuation was noticed with increase in depth of vegetation. The trend shows variation from path to path. Antenna position relative the trees, path geometry and leaf density are all contributing factors that determine excess loss estimation in a typical woodland. Three standard empirical loss prediction models; the FITU-R, MED and COST 235 have been used to evaluate the measurement data. Generally, the FITU-R model, which is a derivative of ITU-R model gave a better fit to the experimental data. The MED and COST 235 repeatedly under-estimated and over-estimated the measured losses respectively. However, these two models (MED and COST 235) occasionally showed good fit when antenna positions relative to the trees are at trunk and canopy levels respectively. Findings in this study bear direct relevance to radio wave propagation in trees and will provide an impetus for accurate design of link budget by radio systems planners.