Phase locking and frequency locking of a 140 GHz klystron and a 280 GHz carcinotron

A phase and frequency‐locked loop to synchronize two microwave tube oscillators for a high density plasma collective scattering diagnostic has been designed, assembled, and tested. A Varian (VRT2121A16) reflex klystron was down converted by mixing with the eighth harmonic of a 17.437 GHz phase‐locked Gunn oscillator, and the resulting baseband was used to lock the klystron phase to a 200 MHz crystal. The down‐converted 140 GHz klystron frequency spectrum shows a linewidth