A Two-Stage High-Gain 10-W Capacitively Coupled Distributed Amplifier Using a New Design Method

For gallium nitride (GaN) high electron mobility transistors (HEMTs) distributed amplifiers (DAs), the relationship between gain and device size is analyzed in this letter when the total gate periphery is a reasonable and constant value. The analysis reveals that gain is a function of device size as the independent variable. With Lagrange analysis, a reasonable design for device size can be obtained to maximize the gain. Subsequently, a novel design method is proposed based on the theoretical derivation, aiming to enhance the gain performance of DAs. To validate the proposed design method, a broadband two-stage high-gain 10-W capacitively coupled DA has been implemented using the WIN 0.25- $\mu \text{m}$ GaN HEMTs process. The measured results of this nonuniform distributed amplifier (NDPA) show a small signal gain of 25 dB, an output power of 10–11 W, and an average power added efficiency (PAE) of more than 25% in the operating frequency range of 2–18 GHz. In addition, the designed NDPA monolithic microwave integrated circuit (MMIC) occupies a chip area of $3600\times 5000\,\,\mu \text{m}^{2}$ .