A method for determining the parameters of the frequency-dependent attenuation model for transmission lines fabricated on printed circuit boards is presented in this letter. The proposed method allows the separate characterization of the conductor and dielectric losses even when the conductor losses present nonideal variation with frequency. Moreover, the steps for implementing a complete model for a transmission line, including the complex propagation constant and characteristic impedance using the extracted data, are also illustrated. Excellent model-experiment correlation for the complex propagation constant for lines fabricated on a printed circuit board technology is achieved up to 110 GHz.