Questions of the experimental determination of the electrical parameters of existing and newly synthesized materials and coatings for microwave frequencies are elucidated. Problems related to microwave measurements of the electrical and geometric parameters of dielectric and magnetodielectric coatings on metallic substrates are examined. An original radio method is proposed for combined measurements of the dependences of the complex dielectric and magnetic permeabilities, as well as the thickness of plane-layered samples of dielectric and magnetodielectric coatings on a metallic substrate. Determination of the electrical and geometric parameters of a coating reduces to minimizing a target function constructed on the basis of the discrepancy of between experimental and computed theoretical values of the field attenuation coefficients for a microwave surface model of the measurements on a grid of discrete frequencies. A simulation model model of the measurements based on the CST Microwave studio (Simulia Corp., USA) and the Matlab system is presented. A simulation model of the measurements is presented based on determining the frequency dependences of the electrical parameters and thickness of a sample of radio-absorbing coating on a metallic substrate. Errors in the estimates of the complex dielectric and magnetic permeabilities in the 9–13.5 GHz band of no more than 10% are found with a confidence level of 0.95 and a mean square deviation in the noise level of 0.006. The proposed method may be in demand in various science-based areas, e.g., microelectronics, aerospace, mechanical engineering, etc.