I. Introduction
Radio frequency power amplifiers (RFPAs), of which the RF power transistor is the essential part [1], are vital components in modern wireless communication. Transistor models play a very important role in understanding and predicting transistor behavior, thus guiding circuit design. Transistors have traditionally been characterized by physical basis models or empirical basis models. However, with the introduction of new materials and the complicated application scenarios, the physical characteristics of transistors have become considerably more complex, making accurate modelling becomes a challenging or even impossible task [2].