Measurements of materials with high dielectric constant and conductivity at ultrahigh frequencies

THE principles for measuring dielectric properties of materials at ultrahigh frequencies are well established.1,2 They are based on measurement of voltage standing wave ratio (VSWR) and location of the standing wave pattern, which results from reflection of electromagnetic waves in front of the sample; see Fig. 1. Transmission line or wave guide sections, depending upon frequency, are used to obtain the necessary 1-dimensional field propagation. The complex reflection factor p, obtained from the measurement as indicated, is related to the dielectric properties of the sample. This relationship permits expressions of the dielectric properties directly, in terms of the observed quantities W = 1 - ρ/1 + ρ (inverse of VSWR) and l0 = x0 + λ/4. For the two most important special cases, sample loaded with either infinite or zero impedance, the relations given in Fig. 2 hold.2 ϵ* is the complex dielectric constant of the sample, ϵ its permittivity, and tan δ characterizes the dielectric losses. It is assumed that the dimensions of the transmission line are unchanged in the sample section, as indicated in Figs. 1 and 2.