The increasing use of microwave signals in consumer electronics has renewed interest in the dielectric properties of materials at microwave frequency bands. The dielectric properties of materials are important parameters in many areas of electronics design, including electromagnetic compatibility, signal integrity, mixed signal circuit, and RF printed-circuit design. Industry and academia therefore require accurate measurement methods for determining the dielectric properties at these frequencies. This thesis builds on an existing dielectric measurement method that is widely considered a very important industry standard for dielectric measurements at microwave frequencies, the split-cylinder resonator method, and improves its capabilities and verifies these improvements experimentally. This method determines the dielectric properties of a flat specimen using the TE0np modes of a resonator, which is formed by the flat specimen and the two halves of a split cylindrical cavity.^ Previous studies have modelled this resonator as a symmetric resonator with two identical halves. This thesis expands the method by using an asymmetric model instead of the symmetric one. This asymmetric model is supposed to account for geometric imperfections of the two halves, and thereby improve the accuracy of the method. Such geometric imperfections, namely slight asymmetries of the two cavities, are very likely to occur if the two halves of the cylindrical cavity have been made with general purpose tooling. This thesis analyses many aspects of the method, including quality factor measurement methods, the coupling of the resonator, and the field configuration of the resonator. Most importantly, it derives a new asymmetric model for the resonator from Janezic¿s mode-matching model. Since this new asymmetric model cannot be used to calibrate the resonant frequencies and the conductor losses of the resonator, a separate model is derived for that purpose.^ Furthermore, the convergence of the asymmetric models is studied. These models were also implemented in software to carry out experimental measurements with a custom measurement setup. This setup was equipped with a novel electromechanical coupling adjustment mechanism to facilitate repeatable measurements. Through an uncertainty analysis of dielectric measurements performed with the new model, it is shown that the model can indeed improve the accuracy of dielectric measurements with a split-cylinder resonator. Additionally, the results of four measurement studies with the new model, which include measurements of microwave substrates and plastics, a repeatability evaluation, and measurements with higher modes, are presented.