Quasi-optical dielectric resonators (QDR) with conducting endplates (CEP) are proposed and justified for measurement of complex permittivity of liquids. The structure of electromagnetic fields in the form of whispering gallery (WG) modes is calculated accurately in terms of Maxwell equations which allow one to characterize liquids from the first principles. A radially two-layered QDR has been shown to be rather convenient for microwave characterization of liquids including ones with large microwave loss. For experimental studies of a number of liquids in K0-band, the QDR in the form of a Teflon disk sandwiched between the duralumin CEP was used. Here, water has shown an unusual property. The sign of the frequency shift indicates that properties of the resonator with waler layer adjacent to the solid state dielectric become nearly the same as with metal layer. The proposed measurement technique can be used also for studies of nonlinear properties of liquids.
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