A reflection method of measuring optical and electrical constants at ultra-high radio frequencies

A source of ultra-high-frequency oscillations was coupled to a long antenna AB at a point O. By terminating one end B of the antenna with a reflecting surface of the substance under investigation, standing waves were produced between the reflector at B and the input at O. Resonance conditions along OB were detected by a thermojunction in the portion OA of the antenna and were controlled by altering the length OB. The phase change Φ produced on reflection was calculated from the difference in the resonant lengths OB with and without the reflecting termination. From the current distribution along OB, the amplitude reduction factor ρ was determined. The electrical and optical constants of the reflecting substance were then calculated from their known relationships to the Fresnel reflection coefficient ρ ejΦ . From the measurements with clay soils with different moisture content it was found that the refractive index increased from 2.6 to 3.6, the dielectric constant increased from about 5 to 11 and the electrical conductivity increased from 1.5×10 9 e.s.u. to 1.8×10 9 e.s.u. as the moisture content of the clay increased. The frequency used was 407 megacycles. It is believed that the values of the phase change Φ were measured to within 1 per cent, and that the amplitude reduction factor ρ was measured to within 3 per cent.