Scattering from Obstacles Over the Earth
Abstract
In Part I of this report the experimental setup and techniques for measuring the fields scattered from a metal circular loop and a straight wire placed above the ground are described. Measured scattered fields (E squared) are presented as functions of loop size, the height of the loop above the ground, and the location of the receiving antenna. The frequency used was 1.5 GHz. Resonant an nonresonant loops and a straight wire a half wavelength long were used. The experiments were performed on an open ground with the scatterer placed less than a third of a wavelength above the ground. The relative complex permittivity of the ground ranged from 5 + i0.6 to 14 + 12.0 or k(g)/k(o) = 2.2 + i0.1 to 3.8 + i0.3, respectively. A theoretical treatment of the scattering from horizontal-wire antennas over the earth is presented in Part II. The well- known electromagnetic fields generated by infinitesimal dipoles in the presence of the earth are reviewed briefly. The fields due to currents in extended conductors can be expressed in terms of an integral over the occupied volume, but its evaluation is possible only when the currents are known in their dependence on the properties of the earth. This is true of the horizontal-wire antenna quite close to the earth, both when driven by a localized emf and when acting as a scatterer in an incident field. Expressions for the most useful component of the radiated or scattered field are formulated for an end-driven Beverage-type antenna and the horizontal-wire as a scatterer in the presence of the earth.
Document Details
- Document Type
- Technical Report
- Publication Date
- Apr 01, 1979
- Accession Number
- ADA069644
Entities
People
- H. M. Lee
- L. C. Shen
- R. W. P. King
Organizations
- Harvard University