Estimation of the Error of the Interference Method for Determining the Dielectric Permittivity on the Example of Transformer Oil in the Ka-Band

We estimate the error of the previously proposed method for determining the dielectric permittivity of liquids on the basis of the interference dependence of the reflected-wave intensity on the thickness of the liquid layer. The frequency dependence of the dielectric permittivity of the VK II A grade transformer oil in the range 26.5–40.0 GHz (Ka-band) is presented. The results obtained by the proposed method and by the method of the open waveguide end are compared to show that they are in good agreement. The behavior of the frequency dependences of the standard deviation and the instrument error is considered. Applicability of this method in the millimeter-wave range is demonstrated.