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. The essential features of the method are the use of a TE sub 01 -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 unexecelled resolution and accuracy in determining the loss tangent even of low-loss dielectrics.