High-power GaN HEMTs battle for vacuum-tube territory

The market for millimeter-wave power amplifiers includes applications in military, commercial and consumer sectors. The armed forces use the devices in transmitters for the detection of small targets and target imaging, in radar equipment, communications and smart weapons systems. In the commercial sector the amplifiers are widely used in high-data-rate communication systems such as digital radio links, SATCOM and wireless LAN, while the consumer market is expected to turn to millimeter-wave systems for applications such as automotive radar. Vacuum tubes are used in the vast majority of highpower amplifiers operating at millimeter-wave frequencies. However, this incumbent technology is under threat from solid-state power amplifiers (SSPAs) that are smaller, cheaper, more reliable and quicker to build. Although these SSPAs could be constructed from GaAs and InPHEMTs, these devices can only operate at low voltages and low powers. These limitations mean that multiple amplifiers or MMICs must be combined in order to deliver the output powers required, which leads to highly complex systems operating at relatively low efficiencies. GaN HEMTs can deliver high powers at higher voltages, and promise simple, efficient millimeter-wave power amplifiers.