High-Performance Space-Qualified Rubidium Atomic Frequency Standard (RAFS)

Excelitas' design has been fully documented and qualified for all space requirements, including radiation. The RAFS offers exceptional performance as a precise time and frequency reference for demanding applications.

The Excelitas Rubidium Atomic Frequency Standard (RAFS) employs classical rubidium gas cell atomic frequency standard principles. It utilizes a physics package with a discrete isotopic filter cell for best stability. The relatively large, cool absorption cell and thin film spectral filter provide exceptionally high signal-to-noise ratio and excellent short term stability. Calorimetric Rb lamp process control and screening assures long life. The "natural frequency" output of 13.4 MHz permits the use of a low complexity, single loop design for improved reliability. Operation at low fixed magnetic bias field improves stability and reduces magnetic and radiation sensitivity. An integral baseplate temperature controller greatly reduces the overall temperature sensitivity by utilizing a thermal insulator that can be tailored to meet various panel operating temperatures. While the RAFS may be operated in air, operating in a vacuum environment that eliminates barometric sensitivity, the extremely low temperature, magnetic, radiation and voltage sensitivities mean that the unit has extremely low sensitivity to all environmental effects, providing a very low flicker floor. The low aging rate of <5x10-14/day is exceptionally smooth and modelable using either a log or diffusion fit to the data.

A crystal oscillator at nominal 13.4 MHz produces the output signal via an output amplifier. This RF output path is hardened against transient radiation. The 13.4 MHz crystal oscillator also excites the Rb physics package via a phase modulator and frequency multiplier chain. This produces a discriminator signal that is processed by a servo amplifier to lock the crystal oscillator to the Rb atomic resonance. Temperature controllers, a lamp exciter and a precision C-field source support the operation of the physics package, while a dc/dc converter and linear regulators provide power for the RAFS circuits. An integral controller stabilizes the RAFS baseplate temperature and several analog monitors are available to assess the operation of the unit.

Key Features

• High-Stability: 2x10-12 at t = 1 second
• Low Power: = 14 watts
• Low Drift: = 5x10-14/day
• High-Reliability: 700,000 Hr MTBF
• Fully Space-Qualified
• Radiation Hardened
• Negligible Environmental Sensitivities
• Small Size: 5.0" x 8.5" x 6.0"
• Low Weight: < 14 lbs.

Applications

• Global Navigation Satellite Systems (GNSS)