A STUDY OF ELECTROMAGNETIC PROPERTIES OF AN ISOLATED TREE
Special technical rept. no. 1941
STANFORD RESEARCH INST MENLO PARK CA
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The objective of the report is to establish an electrical model to represent an isolated tree. Representation of an isolated tree by a perfectly conducting cylinder of smaller radius is shown to be feasible. This leads to the concept of using the equivalent radius of the tree to link the unknown electromagnetic theories of the tree to the well-developed theories of the perfectly conducting cylinder. Data from three kinds of experiments are analyzed to validate the electrical model 1 Patterns of radio waves scattered from an isolated tree and from an aluminum mast, 2 Input impedance of a 12 wavelength vertical antenna in the vicinity of an isolated tree, and 3 Patterns of an isolated tree as a shunt-fed, grounded radiator. The frequencies used in the experiments were 50, 75.1, and 100 MHz the polarization was vertical. The variation of the input impedance of a 12 wavelength vertical antenna as it is moved close to a tree trunk that is similar to that of a 12 wavelength horizontal antenna as it approaches a lossy ground. The directivity of a tree as a shunt-fed, grounded radiator is demonstrated experimentally, and the front-to-back ratio is about 16 dB.
- Radio Communications