The principles and experimental method of investigation of the conductivity and other physical quantities of solid materials are presented. The method is based on the measurement of the amplitude and phase of the transmission coefficient in a coaxial waveguide loaded with sample, which allows the investigation of impedance, admittance, permittivity and electric modulus of the sample over a large temperature range at frequencies ranging from 1 MHz to the centimeter wave region. This broadband impedance spectroscopy method shows advantages over other methods. In particular, it distinguishes between different mechanisms contributing to the charge transport and polarization in materials such as solid electrolytes, ferroelectrics, semiconductors, etc. (c) 2005 Elsevier B.V. All rights reserved.