The Use of Dielectric Lenses in Reflection Measurements

In order to minimize the effects of Presuel diffraction due to short range in the measurement of radar cross sections, a dielectric lens of low dielectric constant was introduced. The lens action was investigated by direct measurement of the shape of the incident phase front at the target, both with the lens in place and without it. The result of the phase measurement showed a reduction of phase variation over the exit aperture of the lens from 150 to 33°. In addition to the measurement of phase, the radar cross section of each of a set of metal cylinders was measured both with and without the lens, for comparison. The measured broadside radar cross section of a cylinder of length equal to about 80 per cent of the lens diameter was doubled by the addition of the lens. Calculation showed that the lens effectively eliminated phase error and that the residual error in measured results was essentially all due to anisotropy of the antenna of the simulated radar system used for the measurements.