  In this letter, we experimentally demonstrate low noise 300GHz wave
generation based on a Kerr microresonator frequency comb operating in soliton
regime. The spectral purity of a 10GHz GPS-disciplined dielectric resonant
oscillator is transferred to the 300GHz repetition rate frequency of the
soliton comb through an optoelectronic phase-locked loop. Two adjacent comb
lines beat on a uni-travelling carrier photodiode emitting the 300GHz
millimeter-wave signal into a waveguide. In an out-of-loop measurement we have
measured the 300GHz power spectral density of phase noise to be -88dBc/Hz,
-105dBc/Hz at 10kHz, 1MHz Fourier frequency, respectively. The free-running
fractional frequency instability at 300GHz is $1 \times 10^{-9}$ at 1 second
averaging time. Stabilized to a GPS signal, we report an in-loop residual
instability of $2 \times 10^{-15}$ at 1 second which averages down to < $1
\times 10^{-17}$ at 1000 seconds. Such system provides a promising path to the
realization of compact, low power consumption millimeter-wave oscillators with
low noise performance for out-of-the-lab applications.
