High spectral purity X-band source

An X-band source that is specifically designed for high order frequency multiplication and precision spectroscopy is presented. The wideband phase noise is controlled by frequency-locking a dielectric resonator oscillator source to a high-Q cavity with a DC loop. This avoids the need for modulation on the source signal that might interfere with high order multiplication. The phase noise close to the carrier can be controlled by phase-locking the 10.6 GHz signal to a harmonic of a low-noise quartz crystal controlled oscillator. Modulation sideband due to the power line and harmonics are suppressed far below the random noise by enclosing the entire source in a magnetic shield. The phase noise is lower than previously published levels of phase noise for a free-running, room temperature, X-band source. In principle the 10.6 GHz signal could be multiplied to approximately 250 THz before carrier collapse would occur. At 250 THz the free-running linewidth would be approximately 2.8 kHz. At a frequency of 30 THz a linewidth on the order of 10 Hz is expected if the phase noise near the carrier is controlled by a harmonic of a low-noise 5 MHz oscillator