FULL-SCALE PATTERN MEASUREMENTS OF SIMPLE HF FIELD ANTENNAS IN A TROPICAL FOREST IN THAILAND
Abstract
During June and July 1966, measurements of the radiation patterns and impedances of selected HF field-expedient antennas were made in a tropical forest in Thailand on frequencies in the range 2 to 15 Mc/s. These tests completed a sequence of measurements on the same and similar antennas (including dipoles, inverted L's, slant wires, and monopoles) in an open, level field, in a U.S. conifer forest, and in a dry-evergreen forest in Southeast Asia. The pattern measurements were made by towing a small, battery-powered transmitter driving a short Hertzian dipole on a long dielectric cable behind an aircraft whose position was electronically tracked. The results are presented as contour maps showing the response for orthogonal polarizations ('vertical,' E sub theta and 'horizontal,' E sub phi) as functions of azimuth and elevation for the elevation range from about 5 degrees to about 55 degrees from the horizon. The power response (normalized Poynting vector) is presented in the same format for the elevation range from 5 degrees to the zenith. Relative gain values are presented for the maximum observed response of the various antennas on a given frequency and for the polarization response E sub theta/E sub phi for a given antenna and frequency. The data indicate that vertical polarization is attenuated more than horizontal polarization, and that scattering of the vertically polarized signal begins at about 12 Mc/s. Impedance data are presented on Smith charts for each antenna over the range of frequencies for which pattern data were obtained. They show that the environment tends to become part of the antenna.
Document Details
- Document Type
- Technical Report
- Publication Date
- Feb 01, 1968
- Accession Number
- AD0674739
Entities
People
- Gary E. Barker
- Glenn D. Koehrsen
Organizations
- SRI International