This document relates to a measurement method for complex permittivity of a dielectric substrates at microwave and millimeter-wave frequencies. This method has been developed to evaluate the dielectric properties of low-loss materials used in microwave and millimeter-wave circuits and devices. It uses higher-order modes of a balanced-type circular disk resonator and provides broadband measurements of dielectric substrates by using one resonator, where the effect of excitation holes and that of fringing fields are taken into account accurately on the basis of the mode-matching analysis. In comparison with the conventional method described in IEC 62810 and IEC 61338-1-3, this method has the following characteristics: " the values of the relative permittivity 5Øß5Øßr2 and loss tangent tan5ØÿÞ5ØÿÞ normal to dielectric plate samples can be measured accurately and non-destructively; " this method presents broadband measurements by using higher-order modes by one resonator; " this method is applicable for the measurements on the following condition: frequency: 10 GHz d"5ØSÜd" 170 GHz; relative permittivity: 1 d"5Øß2 d" 10; loss tangent: 10 4 d"tan5ØÿÞd" 10-2.