This work investigates whether a power amplifier (PA) designed for a lower operating frequency (10GHz) can be effectively implemented using a process that has a 𝑓𝑚𝑎𝑥 of well above 100 GHz. Operating a process far below its maximum frequency offers potential benefits in gain and efficiency, but also presents challenges. Particularly for the stability of the amplifier, which becomes increasingly critical at high gain levels.

To investegate the potential for such an RF power amplifier, Gallium Nitride (GaN) High Electron Mobility Transistors (HEMTs) are used. This is a technology that forms the current State-of-Art for microwave high-power high-efficiency MMICs. The circuit is fabricated using WIN Semiconductors NP12-01 GaN-on-SiC technology with 0.12 𝜇m gates. They offer a technology with one of the shortest gatelengths that are around in the industry.

First a Programme of Requirements was established, before starting the design and four Key Per-formance Indicators (power, efficiency, stability and size) were defined. A design process was followed that started with transistor measurements, after which an architectural design was made, followed by schematic implementation, electromagnetic (EM) modelling and final layout creation. Continuous refinement between schematic, EM and layout stages where necessary to avoid excessive simulation times. After design rule verification and stability checks, the circuit was submitted for fabrication, with MMIC samples received back approximately four months later, after which, an extensive characterization of MMICs was performed, through both small-signal as well as non-linear measurements.

All this work resulted in the following KPI’s:
• For the power, a peak power of over 38 dBm was realized under dedicated measurement conditions and over 35 dBm for nominal measurement conditions (20 V 𝑉𝐷𝑆) and a bandwidth of more than
2 GHz (-1 dB bandwidth) or 3 GHz (3-dB bandwidth) was obtained.
• For the PAE, 35% was nominally achieved over various bias points and frequencies.
• Unconditional stability was achieved.
• The size of the amplifier was 2x1.75 mm2, resulting in slightly below 2 W/mm.

While amplifiers with higher absolute power at X-band exist, the NP12 process is unlikely to surpass the state-of-the-art in this regard due to its limited maximum drain voltage, which constrains the achievable output power. However, the measured efficiency and gain are promising for a first design iteration. Notably, the implementation of the stability analysis for this power amplifier took a significant effort, but was proved highly effective as no instability was observed at all during the measurements. Two variations of the amplifier were implemented to investigate the possibility of reusing the source via-hole for two adjacent output stage transistors. This variation, with re-used via-holes, worked similar to the baseline design, but exhibited a lower PAE.

In conclusion, the expectation is strengthened that the advantages of a mm-wave process used at X-band frequencies can pay off in a modest increase of the efficiency and a significantly increased gain. Finally, the work resulted in one conference publication, and two tutorial documents for future students (an AWR student guide and MMIC mounting tutorial).