A Gunn oscillator at 3 mm waveband phase-locked with high Tc Josephson harmonic mixer and its applications to quantum voltage standard

Using a high-Tc superconducting harmonic mixer at 77 K and a phase-locking loop, a signal source (Gunn oscillator at 3 mm waveband) was directly phase-locked to a local oscillator at the frequency of less than 1 GHz, with harmonic number up to 120. The phase-locked Gunn oscillator achieved the frequency instability less than ±2 Hz, with the counting time of one second, while the phase noise of the signal at intermediate frequency was -59 dbc/Hz (-500 KHz) for 120th harmonic mixing. The output of this signal source was applied to a Josephson junction array used in voltage standard system against which a solid state voltage source (Zener voltage reference) was measured. The experimental results showed that the quality of this phase-locked microwave source was good enough to justify its use in the quantum voltage standard