PRELIMINARY RESULTS OF FULL-SCALE PATTERN MEASUREMENTS OF SIMPLE VHF ANTENNAS IN A EUCALYPTUS GROVE.
Abstract
Preliminary results from check-out tests of a full-scale VHF antenna pattern measuring system including the use of an airborne transmitter (Xeledop) are presented. The tests were made on simple antennas within a grove of eucalyptus trees. Significant perturbations were found in the directivity patterns (normally omnidirectional) of vertical dipoles receiving vertical signals in the forest medium: nulls to 20 dB or more, every few degrees of azimuth, at the three frequencies used, 50, 75, and 100 Mc/s. Directivity patterns of horizontal dipoles receiving horizontal signals in the same forest medium were relatively unperturbed, even at 100 Mc/s. Signal attenuation was greatest in the direction of greatest tree population and most severe for vertically polarized signals. A rough model of the forest medium as a lossy dielectric slab was solved for the attenuation, alpha, of the forest medium. Values obtained are on the order of 0.02, 0.01 and 0.007 neper/meter for vertical, cross, and horizontal polarization, respectively. These values of alpha are compared with measurements of attenuation made at the same site by using an open-wire transmission line in the foliage. Close agreement with the values for cross polarization is obtained. Statistical methods of analyzing antenna patterns for a scattering medium are developed, and their usefulness is demonstrated. Signal expectation level probability distributions are presented for continuously varying azimuth (airborne Xeledop) and continuously varying range (man-pack Xeledop). Considerable agreement is found between these two distributions, both of which seem to be composed of two-sided Gaussian distributions. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 01, 1966
- Accession Number
- AD0484239
Entities
People
- Gary E. Barker
- George H. Hagn
- Harold W. Parker
- James D. Hice
- William A. Ray
Organizations
- SRI International