Semiautomated determination of dielectric permittivity and loss in the microwave region

In a previous publication, apparatus for determination of the complex dielectric permittivity at centimeter wavelengths was described.¹ The geometry used allowed acquisition of a digital record of the power reflected from a short-circuited liquid sample as a function of its length. This experimental procedure is appropriate for samples of moderate to high dielectric loss. For low loss samples, one examines instead the shape of the standing-wave pattern in the transmission line below the termination, liquid lengths corresponding to real terminating impedances being chosen.^2-4 This work is concerned with a modification of the geometry and electronics of the high loss instrument to a configuration which allows a digital record of the standing-wave pattern to be obtained automatically. The system makes feasible the accumulation of large amounts of raw data which are used to average out random errors and to characterize systematic departures from the working equations resulting from nonideal instrument geometry.