Measurement of the complex dielectric constant of very-high-dielectric-constant materials at microwave frequencies

THE MEASUREMENT of the complex dielectric constant of very-high-dielectric-constant materials at microwave frequencies is considerably more difficult than the measurement of materials with a low dielectric constant. The reason for this can be best illustrated by consideration of a commonly used method of measuring dielectric constant at microwave frequencies which is called the short-circuited line method. The equipment used is shown in Fig. 1.1,2 The test sample is placed against a fixed short circuit, and the voltage standing wave ratio (VSWR) and location of the voltage minimum are measured. The complex dielectric constant can be calculated from these measurements. This method is satisfactory for materials where the real dielectric constant is relatively low, but poses serious difficulties for materials where the real dielectric constant is very high. In discussing the reasons for the difficulties, low-loss samples and high-loss samples will be considered separately.