Optical Signal Distribution

Optical  fibre  as  a  medium  for  signal distribution offers key advantages:  it has very low loss, good EMC properties, can support wide bandwidths and is small and light  weight.    The ATC  has  developed distribution networks for both digital and high quality analogue signals.  Illustrated is the Local Oscillator distribution unit from the JORN radar.  This was required to have a  very  low  close  to  carrier  phase  noise performance  (-140dBc@10Hz),  and distribute signals over several km.
Optical Fibre may be used to distribute microwave signals in hostile environments.

The point to point link is designed to carry radar receive signals at 10GHz.  The complete link was subjected to vibration levels appropriate to an airborne environment, and the microwave spectrum measured.  Levels of vibration induced signals were found to be at least as low as measured on an equivalent high quality co-axial interconnect.
As a result of its low loss (0.2 dB/km), optical fibre may be used to carry signals over long distances.  Illustrated is an optical modem, designed and built by the ATC, that carries digital control signals over a distance of approximately 200km without the use of repeaters.  Data is transmitted at rates of up to 50Mbits/s.  This modem is housed on the sea bed, and therefore is required to have very high levels of reliability.
The ATC is developing techniques to combine the advantages of optical fibre distribution and wireless access.  Here fibre provides the backbone of the network, with millimetric radio transmission providing the final drop to the user.  Currently 60GHz systems are being developed, since they provide a wide bandwidth capability, combined with a covert wireless link.  These systems provide well defined cellular coverage, together with good immunity from multipath and Doppler.