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Surrey Satellite Technology Ltd choose European Antennas to design a nadir antenna for the GPS reflectometry experiment on the UK-DMC satellite
Photo taken from UK-DMC satellite of fires in California
Satellite image taken from UK-DMC of fires raging across California.
Nadir antenna installed on UKM-DMC satellite
Three satellites installed in launch vehicle, the UK-DMC is on the left.
Position of antenna.  Launch in preparation at Plesetsk
The concept of using GPS and other signals reflected off the Earth's surface as a method of remote sensing of the environment was proposed originally by the European Space Agency. It was considered possible that reflected GNSS signals might be able to determine sea height, sea state, wind speed, ice and moisture in soil.

Following this hypothesis, and with support from the British National Space Centre (BSNC), Surrey Satellite Technology Ltd (SSTL) has undertaken a spaceborne GNSS reflectometry experiment to investigate the reception of reflected GPS signals off the ocean.  Surrey Satellite Technology modified the GPS receiver on the UK-DMC (Disaster Monitoring Constellation) satellite that they were building to accommodate a downward pointing (nadir) high gain antenna for receiving reflected GPS signals. The modified GPS receiver would then send information to a data recorder to process reflected signals in real time.

Martin Unwin is head of the GPS team at Surrey Satellite Technology and responsible for spaceborne GPS and GNSS receiver design and operation. He chose European Antennas to design the nadir antenna for this experiment "due to our very special requirements".

The antenna had to be GPS L1 LHCP (Left Hand Circular Polarised) as research models indicated that most of the signal received at nadir reflected from the Earth's surface would be LHCP. The antenna would need to have the highest gain possible to maximise the effectiveness of the experiment but must at all costs avoid interference with other antennas on the satellite. It would need a 10 degree offset from bore-site to allow for some yaw steering.

European Antennas worked closely with the team at Surrey Satellite Technology to provide exactly the antenna they wanted to meet the stringent demands of both the rocket launch and the space environment, whilst still operating at optimum efficiency. The final antenna design consisted of a three-patch printed circuit array integrated with parasitic elements to ensure that the bandwidth was met over a wide temperature range and that it fitted neatly in to the satellite. The gain achieved was just under 12dBiC.

The UK-DMC satellite is one of a small constellation of 700km altitude polar-orbiting satellites developed by Surrey Satllite Technology to provide images of disaster areas. UK-DMC and two other satellites - for Nigeria (NigeriaSat-1) and Turkey (BILSAT-1) - were launched via a Russian Kosmos rocket from Plesetsk in Northern Russia on September 27, 2003.  The satellites were successfully delivered into an orbit accurate to within 700 metres.

It has since been reported that all three Disaster Monitoring Constellation satellites are in excellent health and have returned their first test images.

Applications Satellite Communications
2003 - November
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Updated 13 February 2007
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