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Measurements of the complex permittivity ε = ε' – iε'' allow to carry out fast control of the dielectric and semiconductor materials quality. Sometimes, this control measurement may complete or substitute the chemical, physical, optical and others types of analysises. Admixture, added into pure substance, change the significance of complex permittivity. The microwave measurements of ε' and tgδ may be used by the chemical, food and others industries to control technological processes, and by the research laboratories, which need in the information about the sub-stance characteristics. The waveguide and resonant-cavity methods of dielectric constants measurements are the most widely used methods. They allow to comprise the wide band of values of Dielectric Constant and Loss Tangent and do not demand special equipment. For the complex permittivity measurements equipment for research of feed lines and antennas at microwave frequencies may be used. The Resonant- Cavity method provides relatively high precision of permittivity measurements for dielectric substance with low Loss Factor (tgδ < 0.01) and Dielectric Constant, from 1 to 40. This method allow to measure parameters either of the separate specimen, or parameters of substance in the torrents (for the liquid and powder substances). The Waveguide method allow to measure ε' and tgδ practically of all dielectric materials. The specimen may be situated in the waveguide [1, 2] or in free space [5].