A Design of X-Band 40 W Pulse-Driven GaN HEMT Power Amplifier

In this paper, a systematic design of X-band (9-10 GHz) 40W pulse-driven GaN HEMT power amplifier is presented. The design includes device evaluation, verification of designed matching circuits, and measurements of the designed power amplifier. Firstly, the optimum input and output impedances for the selected GaN HEMT chip from TriQuint Semiconductor Inc. are evaluated using load-pull measurement. The selected GaN HEMT shows extremely low optimum impedances, which are obtained using a pre-match load-pull method due to the limitation of the tuning impedance range of conventional impedance tuners. We propose a novel extraction of the optimum impedances with general pre-match circuits. The extracted optimum impedances are found to be close to those computed, using the large signal model supplied from TriQuint Semiconductor. Using the optimum impedances, the matching circuits of the power amplifier are designed employing the combined impedance transformer type based on EM co-simulation. The fabricated power amplifier has a size of 15 x 17.8 mm(2), an efficiency above 45%, power gain of 7.7-9.9 dB and output power of 47-44.8 dBm at 9-10 GHz with pulse width of I mu sec and duty of 10%.