Abstract <p>Addressing unresolved issues in microwave electrotechnology, related to mathematical modeling and development of systems or technologies for exposure of materials to an electromagnetic field, requires knowledge of the dielectric properties of high-energy microwave-absorbing composites. In this paper, we present calculation results and experimental data on the dielectric properties of epoxy-matrix composite materials containing various fillers. The dielectric properties of the materials were studied by a waveguide method based on determination of the complex reflection and transmission coefficients of electromagnetic waves in a working chamber containing a sample to be studied. Modeling the electric field distribution, we have optimized the electromagnetic wave geometry in a measuring microwave line (frequency of 2450 MHz). The use of silicon carbide as an absorbing filler in the composite has been shown to ensure a high temperature of its heating through microwave energy dissipation. In addition, the results of full-scale measurements of the dielectric properties of the composites having different fillers agree with those of numerical experiments to within 14%. The results we obtained can be useful in designing new microwave-absorbing polymer-based composites with tailored functional properties.</p>