Universal Curves for Dielectric-Filled Wave Guides and Microwave Dielectric Measurement Methods for Liquids

Abstract

The characteristics of wave guides containing a non-ideal dielectric medium are expressed in terms of a dissipation factor, D, the effect of which is analogous to that of the loss tangent of the medium, tanδ, for coaxial or two-conductor transmission lines. A set of universal curves may then be constructed for the variation of the wave-guide parameters as functions of the dielectric loss factor in terms of D. These curves are independent of the dielectric constant, ε′, and of the frequency and mode of operation. An experimental method is described for the measurement of the dielectric constants of medium and high loss liquids using a variable length of liquid dielectric column contained in a section of wave guide or coaxial line and terminated by a perfectly reflecting plane. Either a unidirectional coupler or slotted line may be used to observe the variation of the magnitude of the reflection coefficient with the dielectric sample length. An exact analytical expression is given for the determination of the constants of the medium using the dielectric constant, ε′, and the dissipation factor, D, as the primary independent parameters instead of ε′ and tanδ. A graphical method of solution is also given.