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The measurement of complex permittivities of isotropic media at microwave frequencies is performed with high precision by means of cylindrical cavity resonators. However, a hole in the cavity wall, for inserting the sample causes a frequency pulling of the resonator, which in turn introduces an error in the measured dielectric constant. These effects are measured, and with perturbation theory as a guide, correction factors are developed.
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Bussey et al. (1960) studied this question.
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