MILLIMETER-WAVE AND MICROWAVE MEASUREMENTScorrection taking into account the additional volume of sample extending beyond the curved phase front normally assumed in the beam wave theory has been suggested by Cook and Jones (47). The applicability of the open resonator technique has been extended up to 140 GHz by the same authors (48). Very similar hemispherical resonators were used by Chan Song Lint and Priou (49) for characterizing magnetic materials in the 36-90 GHz range. Another open resonator was also used up to the submillimeter range by Volkov et al. (50).