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Millimeter-Wave Measurement of Complex Permittivity by Perturbation Method Using Open Resonator

This paper explains how better accuracy can be achieved in measurements of the complex permittivity (relative dielectric constant epsivr ' and dielectric loss tangent tan delta) of thin films having a thickness in the range of 10-100 mum. Specimens to be measured using a conventional open-resonator method need to have a thickness that is an integral multiple of a half wavelength, so specimens thinner than this half wavelength cannot be measured with an open resonator. However, the use of the perturbation method made it possible to obtain values of complex permittivity of ultrathin specimens of materials such as polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP), and PTFE including glass fiber used for printed circuit boards identical to those obtained for thick specimens.