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

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Abstract
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.

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