A Straightforward Fitting Strategy Based on the Complex Lorentzian Function to Fully and Systematically Characterize the Kink Effect in the Output Reflection Coefficient of the GaN HEMT Technology

Understanding the frequency-dependent transistor performance is essential to making the best use of this component for the purpose of designing an effective microwave circuit. This work is prompted by this point and focuses on the analysis of the kink effect occurring in the output reflection coefficient ($S_{22}$) of microwave transistors. A systematic method based on the complex Lorentzian function is developed to straightforwardly fit the frequency-dependent behaviour of $S_{22}$ and, in turn, to effectively determine a set of parameters for an accurate and complete characterization of the kink effect. To validate the proposed methodology, the gallium-nitride high-electron-mobility transistors (GaN HEMT) technology is taken into consideration as a case study. Investigating the frequency-dependent behavior of GaN HEMTs is especially critical for aerospace radar and communication applications. A complete and accurate device characterization across a wide frequency range is crucial to achieving reliable high-frequency performance in such complex and demanding systems.