Superconducting-cavity stabilized oscillators with improved frequency stability

X-band microwave oscillators stabilized with superconducting niobium cavities with loaded Q's of about 10
¹⁰
achieved short-term frequency stabilities as low as σ
y
=6 × 10
^-16
, and typical long-term fractional frequency drifts of ± 2 × 10
^-13
per day.