An X-band class J GaN amplifier for radar remote sensing using >50 VDC FETs

A novel GaN technology for high power and high efficiency amplifiers operating in X-band is presented, which is ideally suited for radars used in remote sensing applications. Unlike state-of-the-art GaN-SiC technology operating at 28-40 V, the proposed devices operate at > 50 V bias to achieve high power density while still achieving relatively high efficiency. A prototype GaN-SiC device of 9.6 mm gate periphery and 3.2 pF output capacitance achieves > 80 W output power (> 8 W/mm or 25 W/pF) at 7.9 GHz with a radar pulse width of 35 μs and a duty cycle of 30%. Operating bias on the reported results ranges from 65 to 75 V. Higher voltage operation has the advantage of achieving higher power density and lower capacitance/Watt, but requires some form of circuit enhancing technique to maintain high efficiency. Several efficiency enhancing techniques have been successfully utilized at lower frequency in UHF, L and S-bands; these techniques operate the amplifier in class E, F or inverse F and require proper multi-harmonic tuning. At high frequency in upper C-band and X-band these approaches tend to become less effective. Therefore, in this paper efficiency enhancing techniques based on reactive load impedance at the fundamental as used in class J amplifiers is explored. The work is part of an SBIR Phase I award from Jet Propulsion Laboratory / NASA to Integra Technologies, Inc. with the objective of designing and building a 400 W power amplifier in X-band with 30% duty cycle and >40% power added efficiency (PAE) for space exploration.