For electronic technology, it is necessary to have information about the electrodynamic parameters of the materials used at standard and high temperatures. Various methods and setups are used to heat material under test samples. The proposed design uses convection heating of the material placed in the measuring waveguide. Material characterization using a transmission line and a vector network analyzer allows one to obtain electrodynamic parameters of the material under test over a wide frequency range. The proposed setup makes it possible to determine the electrodynamic parameters of dielectrics with high precision. The algorithm for evaluating the complex dielectric permittivity is based on the Nicolson-Ross-Weir method. Raw method shows a large spread in the calculated electrodynamic parameters. It is necessary to consider the size change of the measuring line due to the temperature to obtain correct data. The paper shows that calculation of the effective dimensions of the waveguide influence the measurements results. © 2022 IEEE.