Analysis of a GaN/SiC UHF radar amplifier for operation at 125V bias

The relationship between Fe concentration in the buffer layer and breakdown voltage of an AlGaN/GaN on SiC HEMT transistor has been investigated to achieve operation of the device in a UHF power amplifier operated at a bias of 100V or higher. A 15mm transistor has been tested in a power amplifier at the frequency of 430MHz with a 100μs pulse and 10% duty factor, operated at 75V, 100V, 125V and 150V bias. At 100V bias, the device achieves 250W output power and 78% drain efficiency with 27dB gain almost independently of Fe content; at 125V bias, only the devices with Fe content above 1e18 cm^-3 achieve a saturated power in excess of 350W with 75% drain efficiency and 27dB gain. RF burn-in tests indicate very stable operation. To the authors´ knowledge, this is the first time that UHF pulsed radar amplifier operation has been reported at voltages above 100V with GaN technology.