A 15-W X-Band Inverse Class-F GaN Power Amplifier With Second-Harmonic Input Tuning

This letter presents an inverse class-F power amplifier (PA) where the second-harmonic voltage produced by the nonlinear gate-source capacitor ( C_\text{GS} ) of the gallium nitride (GaN) HEMT transistor improves the PAE and output power. The design is based on multiharmonic recursive source-pull (SP) and load-pull (LP) simulations to determine the optimum design space. With proper impedance terminations at f_\text{0} and \text{2}f_\text{0} , the second-harmonic input voltage improves the PAE by about 10%. An X -band proof-of-concept PA is implemented in a 250-nm GaN technology with a f_\text{max} of 50 GHz. At 9.5-GHz center frequency, 17.8 W peak output power and 43 \% power added efficiency are achieved for pulsed-mode operation with a pulse repetition frequency of 10 kHz and a duty cycle of 10 \% . The designed three-stage PA consumes 7.72 mm ^\text{2} die area and dissipates about 39 W dc power at saturation.