A study for achieving high power and efficiency based on high bias operation in C- and X-band GaN power amplifiers

An RF GaN technology is introduced for C and X-band high power radar transmitters that has the potential of offering an intriguing and effective alternative to high power travelling wave tubes (TWT). GaN technology targeted for C and X-band amplifiers typically operates from a supply voltage ranging from 28 V to 50 V, depending on signal and application. The present research work reports a 120 W pulsed prototype amplifier for C-band which utilizes a 0.25 Jim GaN process operating at 90 V bias. A similar but smaller 28 W prototype is also reported at 10 GHz with an operating bias of 75 V. High bias at higher frequency achieves higher power density at the expense of lower efficiency; however, for applications requiring hundreds or thousands of watts power level typically provided by TWT the combining losses from lower voltage and lower power transistors result in degraded system efficiency. Higher voltage power transistors require less combining and result in smaller and lighter amplifier modules, which make the exploratory study on high voltage operation at C and X-band relevant and interesting.