Complex permittivity measurement of dielectric materials using nonradiative dielectric guide at millimeter wavelength

In this paper, as a method for measurement of complex permittivity of millimeter‐wave dielectric materials, a transmission resonator method is proposed which is made of a dielectric resonator with both sides open placed in a nonradiative dielectric (NRD) guide. For the evaluation of the surface resistance of the conductor indispensable for measurement of the complex permittivity, a pair of TEoml mode resonators are placed coaxially and are mutually coupled. The difference of the conductor losses for the even and odd mode resonances of this resonator system is detected as the difference of the unloaded Q's so that the surface resistance is derived. The special features of the present measurement method are to evaluate the conductor surface resistance at a high sensitivity in a condition close to the resonator with both ends short‐circuited and to use a resonator with both ends open‐circuited for sample measurement because the effect of the surface resistance is small so that high accuracy is obtained as a whole. By using an NRD guide excitation method, a measurement system is realized which affects very little the unloaded Q of the resonator system and the electromagnetic field distribution. For the calculations of the complex permittivity, the eigenvalue calculation by the finite element method and the perturbation method by Kajfez are combined. For the samples with its relative permittivity of 24 and the loss tangent of 2 × 10−4, the measurement fluctuations are less than 0.005 percent for the resonant frequency and less than 1 percent for the unloaded Q. The measurement accuracy for the relative permittivity is less than 0.4 percent and that for the loss tangent is less than 3 percent.