Class F and inverse F power amplifiers
They use polyharmonic resonant striplines to tune harmonics.  e.g.  A gate voltage condition to meet is that the impedance is a short circuit at the third harmonic.

e.g. a bare-die, Cree CGH40010F  model is developed for this transistor is focused on accurately predicting the on-off regions of the transistor characteristics as a switch.

An infinite number of odd-harmonic resonators results in an idealized Class F mode with a square voltage waveform and a half-sinusoidal current waveform at the device output terminal.

An infinite number of even-harmonic resonators
results in an idealized inverse Class F mode
with a half-sinusoidal voltage waveform and a
square current waveform at the device output
terminal