Accession Number : AD0484239

Title :   PRELIMINARY RESULTS OF FULL-SCALE PATTERN MEASUREMENTS OF SIMPLE VHF ANTENNAS IN A EUCALYPTUS GROVE.

Descriptive Note : Special technical rept.,

Corporate Author : STANFORD RESEARCH INST MENLO PARK CA

Personal Author(s) : Hagn, George H. ; Barker, Gary E. ; Parker, Harold W. ; Hice, James D. ; Ray, William A.

Report Date : JAN 1966

Pagination or Media Count : 126

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)

Descriptors :   (*ANTENNA RADIATION PATTERNS, TREES), VERY HIGH FREQUENCY, PORTABLE EQUIPMENT, AIRBORNE, TRANSMISSION LINES, ATTENUATION, STATISTICAL ANALYSIS, MEASUREMENT, INSTRUMENTATION, DIPOLE ANTENNAS, POLARIZATION.

Subject Categories : Radiofrequency Wave Propagation

Distribution Statement : APPROVED FOR PUBLIC RELEASE