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The purpose of this study is to present an advanced technique for accurately modeling the behavior of a GaN HEMT under realistic working conditions. Since this semiconductor transistor technology has demonstrated to be very well suited for high-frequency (HF) high-power applications, an equivalent circuit model is developed to account for the device nonlinearities at microwave frequencies. In\ud particular, the proposed model includes bias dependence of both low-frequency (LF) dispersive effects affecting GaN devices and HF nonquasi-static effects, since these two types of frequency dependent\ud phenomena play a crucial role under microwave large-signal condition. The extraction procedure consists of two main steps. First, an accurate multibias small-signal nonquasi-static equivalent circuit is analytically extracted from scattering parameters measured under a wide range of bias points. Thereafter, this linear model is used as a cornerstone for building a nonlinear nonquasi-static equivalent circuit, which is expanded to account for the LF dispersive phenomena by using an empirical formulation directly identified from the HF large-signal measurements. The accuracy of the proposed modeling approach is completely and successfully verified by comparing model simulations with LF and HF large-signal measurements

In this work a de-embedding technique oriented to the evaluation of the load line at the intrinsic resistive core of microwave\ud FET devices is presented. The approach combines vector high-frequency nonlinear load-pull measurements with an accurate\ud description of the reactive nonlinearities, thus allowing one to determine the actual load line of the drain–source current generator\ud under realistic conditions. Thanks to the proposed approach, the dispersive behavior of the resistive core and the compatibility\ud of the voltage and current waveforms with reliability requirements can be directly monitored. Different experiments\ud carried out on a gallium nitride HEMT sample are reported

A X-band GaN monolithic microwave integrated circuits (MMIC) High Power Amplifier (HPA) suitable for future generation Synthetic Aperture Radar systems is presented. The HPA delivers 14 W of output power, more than 38% of PAE in the frequency bandwidth from 8.8 to 10.4 GHz. Its linear gain is greater than 25 dB. For the first time an MMIC X-band HPA has been designed by directly measuring the transistor behavior at the current generator plane. In particular, optimum device load-line has been selected according to the chosen performance tradeoffs