Abstract :
The paper describes an experimental determination of the usefulness and limitations of elementary theory in estimating the fields scattered by metal wires and sheets, treated as passive scattering-elements. The results are of interest in assessing errors due to obstacles on a direction-finding site. Formulae are derived for the scattered fields, using the transmission-line theory for wires and diffraction theory for sheets. A method is described for the measurement of scattered fields and the results of measurements on various wires and sheets, at a frequency of 600 Mc/s (50 cm), are shown to be in substantial agreement with the elementary theory. The measured amplitudes of the resonance peaks which occur in the field scattered by a wire as the length of the wire is varied are, however, much smaller than would be expected, except for wires less than two wavelengths long. The results indicate that for wires of the order of 1-mm diameter resonance effects at a frequency of 600 Mc/s are small if the length of the wire is more than about five wavelengths. This conclusion is probably true for a wide range of wire diameters and frequencies. Resonance effects in sheets may be neglected if the dimension of the sheet normal to the electric vector is greater than a wavelength. It is concluded that scattered fields may be computed from elementary theory to the accuracy normally required in direction-finding work.
