This paper presents a broadband technique for determining the intrinsic electromagnetic properties of isotropic thin-film materials in the 50 to 75 GHz frequency range. The cell used is a microstrip line produced onto the sample to be studied. A measurement bench with a high quality ridged to microstrip transition covering 50 to 75 Ghz is developed. The complex properties of the sample under the test are computed from S-parameters and a processing method taking into account the dominant mode propagated into the microstrip cell. Measurements in V-band of alumina show a good agreement between measured and predicted data.