The paper is received on June 14, 2016

Abstract. An original method is developed for determining the loss tangent (tand) of thin dielectric plates and films in the millimeter and submillimeter ranges. The method is based on comparing the Q factors of an empty semisymmetric confocal open resonator and a resonator in which a sample under test is placed near the plane mirror. The change of losses in the resonator due to the insertion of a sample is represented as a difference between the reflection losses from the plane mirror and from the sample placed in front of the mirror. The additional phase shift due to the insertion of a sample into the resonator is compensated for by a decrease in the resonator length. The loss tangent tand of thin films was measured in the cavity resonator at 69.4 GHz. To determine the refraction index of the films, a method is proposed that is based on measuring the reflection coefficient of a plane electromagnetic wave formed by the horn-lens system incident on a sample. The refraction index is measured at frequency of 103.1 GHz. The method is applied to measuring the parameters of Mylar films of various types and thickness (from 20 to 250 mm). The data obtained allowed one to calculate the characteristics of quasioptical beam splitters (the reflection coefficient into a side channel and transmission through the working channel). An algorithm is developed for calculating the characteristics of beam splitters, and the characteristics of beam splitters are measured for films of various thicknesses at frequency of 92 GHz. The reflection coefficients of the film and a metal plate are compared for TE and TM waves incident at 45^o. When measuring the transmission coefficient, the amplitude of the transmitted wave is measured for a film situated at 45^o to the incident wave and without the film.

Key words: dielectric films, dielectric permittivity, open resonator, quasioptical methods of measurement, millimeter waves.

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