Microwave measurement of dielectric properties using the TM011 and TE011 modes excited by a generalized nonradiative dielectric resonator

This paper proposes a new method for measurements of dielectric properties at microwave frequency. The measuring structure is a nonradiative dielectric resonator which is made up of a circular-symmetry cross shaped dielectric and two conducting plates each having a center hole. The dielectric is sandwiched between the two metal plates. Both the resonant TM011 and TE011 modes can be applied in this resonator. The radial mode matching method is employed for analyzing the field distributions, while the transmission-mode Q-factor measurement technique is used for precise determination of unloaded Q(0)-factor. Complex permittivities of several plastics, such as high-density polyethylene, cross-linked polystyrene, polytetrafluoroethylene and polycarbonate, are measured at room temperature. Their accuracies are justified by comparing the results with those obtained by other well-known techniques. An uncertainty analysis is also presented to estimate the errors resulting from the uncertainties in structure dimensions, resonant frequency, unloaded Q(0)-factor and conductivity of the metal plate. With this resonator, an accuracy of better than 1.5% is attained in real permittivity, while the uncertainty in loss tangent is within 2.5% for dielectric with loss tangent greater than 5.0 x 10(-4). For material with lower loss, e. g. tan delta similar to 10(-4), the measurement uncertainty in loss tangent would not be greater than 10%. This larger uncertainty in loss tangent for materials with lower loss is mainly due to the uncertainty in conductivity of the metal plate.