Power-Dependent Modeling of Microwave FET Intrinsic Elements Using X-Parameters

This study introduces and validates an alternative approach for modeling microwave FETs using power-dependent electrical equivalent circuits extracted from conventional X-parameters (Z_L = 50 Ω). The proposed method expands the use of the conventional X-parameters measurements by generating a model that is more practical and intuitive. It enables the extraction of intrinsic elements through a procedure similar to that used in small-signal analysis. Moreover, the nonlinear intrinsic elements are expressed as functions of input power, and the resulting model can be readily implemented in commercial microwave simulators. Experimental validation using the GaN FET CGH40010F demonstrates that the proposed model achieves improved prediction accuracy for power-added efficiency (PAE) and drain efficiency compared to the manufacturer's model. One-tone test errors are below 5 dB, PAE prediction errors are under 2%, and the estimation of the optimal load impedance for maximum PAE is significantly more accurate with the proposed model.