Measurement of v.h.f. complex permittivity of liquids by means of an adjustable coaxial line

Methods of measuring the complex permittivity of both liquids and solids at coaxial-line and waveguide frequencies are well known. The most usual procedure is for the line or guide to be terminated by a short-circuited section of fixed length containing the dielectric material being investigated. However, another possibility, in the case of liquid dielectrics, is that the termination should be a short-circuited section of variable length. The purpose of this paper is to examine theoretically the relationships between the complex permittivity of a liquid being investigated by the latter method, using a coaxial line, and the standing-wave ratios measured in the air-filled portion of the line. Graphs are given which, drawn accurately to a suitable scale, have been used as charts by the authors.