A method for determination of the complex dielectric permittivity of polar, nonpolar and ion-containing polymers at microwave frequencies is presented. Disk-shaped samples are employed in a radial-line configuration at the end of a coaxial-line structure. An equivalent circuit, established by admittance measurements, is used to relate the capacitance at the sample face to the impedance measured on the slotted line preceding the coaxial sample holder. The method has been applied first to determine the frequency spectrum of polyethylene (PE) and poly(tetrafluoroethylene) (PTFE) between 80 MHz and 4 GHz at 293 K. The results agree with those reported in the literature, demonstrating the reliability of the method as well as usability of PE and PTFE as standards at high frequencies. Subsequently, the AMF C-311 cation exchange membrane [polyfluorocarbon backbone chains with grafted polystyrene side chains containing sulfonate groups] was studied in the same frequency range. Values of dielectric permittivity and dielectric losses for AMF C-311 samples in the dry and swollen hydrated states are reported and compared.