Microwave Source

Microwave source CAD  Microwave source CAD
Microwave source SH CAD model (made by Thales TAS)

The main characteristics of the Microwave Source are:

  • a low power spectral density of the phase fluctuations
  • a frequency resolution of 10-5 Hz
  • output interrogation and selection signals: 0.01 nW to 10 mW
  • less than 2.10-11 sensitivity to environment over 90 min.
  • a USO frequency correction via a DDS
  • a synchronization signal (100 MHz/12) to the UGB

The Microwave Source is composed of an ultra-stable oscillator (USO) and a frequency synthesis chain. Thales TAS (Thales Airborne Systems) is responsible for the Microwave Source, and CMAC, the subcontractor of Thales Alenia Space (TAS), for the USO.
The frequency chain synthesizes two signals at 9.192631770 GHz from a 5-MHz ultra-stable quartz oscillator.
The low-noise 9.192631770 GHz output frequency is obtained from a 5-MHz reference in two steps: a phase locking of a 100-MHz VCXO and a phase locking of a 692-MHz VCO.
The microwave source has two direct digital synthesizers (DDS): one is used to compensate the frequency drift of the USO, the other allows a fine frequency adjustment in steps of 10-5 Hz of the 9.192631770 GHz to obtain a resolution of 10-15 of the clock frequency.


The measured power spectral density of the phase fluctuations in accordance with the Fourier frequency for the flight model (FM) is:

Power spectral density of the phase fluctuations
Power spectral density of the phase fluctuations

Microwave Source
Microwave Source

Main characteristics

  • size: 270 x 300 x 103 mm³ (8 litres)
  • weight: 7.03 kg
  • power consumption: 24.5 W

The contract was awarded to Thales in 2001. The PDR was completed in 10/2001 and the CDR in 05/2004. The main deliveries were the STM in 12/2002, the EQM in 02/2004 and the FM in 12/2004.

Main challenges: micro-vibration sensitivity. The micro-vibration impacts on PHARAO’s Microwave Source are mainly the degraded microwave stability due to the USO’s sensitivity to microgravity.

A LSA (Low Sensitivity to Acceleration) USO became available in 07/2005. This LSA USO replaced the FM 34 in 2006.