On the Electromagnetic Field Radiated above the Tree Tops by an Antenna Located in a Forest
ARMY ELECTRONICS COMMAND FORT MONMOUTH NJ
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Theoretical investigations of the field in forest environments have usually considered the case where both the transmitting antenna and the receiving terminal were located within or very close to the vegetation. The present work examines the case where one of the two antennas is located inside the forest while the other is situated above the tree tops. The mechanism of wave propagation and its effect on the field variation are discussed for heights that start at the forest-air interface and extend vertically to large elevations. It is shown that the field just above that interface and up to a critical height H sub c is dominated by a lateral wave. Above the height H sub c, the field is given by a refracted line of sight wave whose amplitude is subject to a strong height gain effect. This gain continues up to a height H sub m above which the field starts decreasing monotonically. Both vertical and horizontal polarizations are examined and typical results are given for several representative forest varieties. While the present results extend certain conclusions obtained from previous work, they also represent an important first step in solving communication problems involving mixed paths which cross partly through vegetation and partly through air or clearings.
- Radiofrequency Wave Propagation
- Radio Communications