By Tom Dekker, Cree
In the early 2000s, military designers developing the next generation of high-frequency, high-power amplifiers for radar, communications and EW equipment had reached the performance limits of conventional technologies, namely Traveling Wave Tubes (TWTs), silicon Laterally Diffused Metal Oxide Semiconductor (Si LDMOS) transistors, and gallium arsenide (GaAs) MESFETs. Because these next-generation systems required higher efficiencies, higher power ratings, increased bandwidth, and a smaller device footprint, design engineers started to adopt gallium nitride (GaN) high electron mobility transistors (HEMTs) to replace the older technologies.
Although still a new technology in the mid-2000s, GaN HEMTs exhibited distinct performance advantages when compared to the older technologies. GaN devices offered high voltage, high power density capabilities that allowed amplifier designs high power with increased bandwidth at efficiencies (as much as 50% higher) than conventional silicon or GaAs devices. Also, these high voltage devices exhibited high transistor impedances that enabled broadband matching, and facilitated rugged withstand capabilities to high VSWR load mismatches. These characteristics enabled design engineers to reduce the size, weight, and complexity of their transmitters and thermal management, especially when compared to the older deployed systems.