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
$f_{{0}}$
and
${2}f_{{0}}$
, 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 mm2 die area and dissipates about 39 W dc power at saturation.