An Improved Method for Measuring the Complex Permittivity of Lossy Dielectrics at Millimeter-Wave Frequencies.

An accurate knowledge of the complex permittivity of dielectric materials is of importance at millimeter-wave frequencies for a number of applications. Since conventional lower-frequency techniques are not of use above 30 GHz, a special method for measuring such parameters was developed and is presented in this paper. The essential features of the new method are the use of a TE0l -mode resonant cavity, which virtually eliminates the effects of any thin air gap separating the dielectric sample from the waveguide walls- and the evaluation of the loaded Q factors by a spectral-domain technique yielding unexcelled resolution and accuracy in determining the loss tangent even of low-loss dielectrics.