Air Traffic Safety Electronic Engineers of Hellenic Civil Aviation Authority provide maintenance, repairing and upgrading of the Surface Movement Radar, ASTRE2000 of THALES Company, which has already installed in the Tower Control and Communicaton building of Athens International Airport. This Radar in combining with A-S.M.G.C.S. (Advanced Surface Movement Guidance Control System ) of Navia(Park Air Systems)  Company allow the Air Traffic Controller to 'see' in real time the Aircrafts and Vehicles movements into the airport control area. The above Radar installed to coverage the operating requirements of the Athens International Airport, Eleftherios Venizelos.

The ASTRE2000 Radar is an Airport Surface Detection equipment designed for the surveillance of aircraft and vehicles on the ground. As air traffic continuously increases, new facilities are required to handle traffic and maintain safety on the ground as in the air.

Major international airports frequently have two or more runways sustaining fast turnover, a complex network of busy taxiways, several terminal buildings with a large number of gates  and aprons. The ground movements of many aircraft and vehicles are difficult to control because of the size of the area, masking obstacles or reduced visibility during rain or fog periods.

During periods of reduced visibility, it becomes uneasy to maintain a satisfactory traffic flow while keeping the requested safety standards. Appropriately sited ASTRE radar can improve both safety and efficiency of airport traffic by providing the ground controller with a clear picture of the areas, not in direct line-of sight from the tower cab or under poor visibility conditions.

The radar gives an accurate picture of aircraft position, shape and heading. The trail of past positions gives information on aircraft or vehicle displacement in heading and speed.

The radar display gives position plots and a map of runways, taxiways and parking areas. Radar echoes not being of interest (out of traffic areas or fixed obstacles) are eliminated so that the operational picture is kept as clear as possible.

Efficiency of the ASTRE radar has been proven under the most extreme conditions of rain and snow where it shows a constant high level of performance in range and target visibility.

Such equipment reduces the controller's workload and makes it possible to maintain a required traffic level in conditions of reduced visibility. It enhances safety by ascertaining that taxiways or runways are free from obstructing traffic, gives information on ground separation and a survey of the ground movement situation.

• The antenna has an azimuth beamwidth of 0.33 ° to provide h accuracy and resolution.
• The vertical beam is better than 3.5 ° in width. It has an underside cosecant shape to reduce the size of rain cells and contribute to high detection performance under heavy rain.

• A 60-RPM  rate provides fast position updates as required take-off and landing survey. The antenna is housed in a radome to avoid excessive driving power and to protect the antenna from icing and unbalanced dynamic loads.

• Two transmitters operate at two different frequencies in the 15.7 to 16.7 GHz band, with sufficient separation to provide an efficient diversity improvement  (the diversity gain is provided both additional transmitted power and by the uncorrelated addition returns). The improvement over single frequency operation is 6.3 d.

• The transmitted pulse width is 40 nsec nominal with a 8192Hz PR>
• PRF staggering and video correlation eliminates second time around echoes.
• Range accuracy and resolution are improved by a specific pulse shaping.
• Azimuth accuracy and resolution are improved by beam sharpening.
• Video processing is performed on a 3-fold expanded signal.

Three processes are applied to expanded video depending on the area of detection:
 

• Area 1

• Area 2

• Area 3

The ASTRE Airport Surface Movement Radar (SMR) uses a radar sensor operating in the Ku-band. It provides high resolution, clutter free surveillance information on aircraft and vehicles, on the airport movements and adjacent areas under all weather and visibility conditions. Redundancy is provided throughout the system in order to comply with availability requirements.

Ku-band and frequency diversity

The ASTRE 2000 radar operates in the Ku-Band (15.7 to 16.7 GHz). This frequency band presents a perfect trade off between required beamwidth for a high definition radar, reasonable antenna dimensions, atmospheric attenuation and rain clutter reflections. Following early THOMSON-CSF research on this radar design in the late seventies, this frequency band was finally adopted by the FAA of the USA. 
It should be noted that the Ku-band has been allocated for the detection of ground vehicles by the I.T.U. (International Telecommunication Union).

The ASTRE 2000 radar is operating in frequency diversity.
Two transmitters operate at different frequencies in the 15.7 to 16.7 GHz band, sufficiently separated to provide a diversity effect. The detection gain under these conditions is not only due to the additional transmitted power,  but also because clutter returns at the different frequencies do not sum, whilst the target returns are coherent and summed. This gives an overall diversity gain of 6.3 dB compared to a single frequency, single transmitter configuration.

A high performance reflector antenna under radome (SEE figure)

The ASTRE reflector antenna is one of the most critical components of the radar system since it determines both the azimuth resolution and the level of clutter intake.

The reflector antenna combines a very high nominal gain of 43 dBi with narrow azimuth beamwidth (0.33 °) and low side lobes.

The combination of a high gain antenna with a high receiver sensitivity gives high performance in range even under heavy rain conditions.

Similarly, a 3 ° (typical) elevation/beamwidth proved to be an optimum trade-off between a narrow elevation beamwidth (thus reducing the level of clutter intake) and the size of the vertical aperture of the antenna.

Finally, the elevation pattern shape (cosecant 1.4) results from extensive analysis to optimize the signal/noise ratio over the entire range from 0 to 5000 metres.

A high rotation rate of 60 RPM provides fast position updating necessary for the surveillance of take-offs and landings.

The antenna is housed in a radome to avoid excessive drive power and to protect the antenna from weather and possible unbalancing aerodynamic loads.

The offered radome is of sandwich type. It does not alter antenna performances.

A fully digital processing

The ASTRE features full digital processing:

• Range and azimuth filtering for discrimination enhancement:
• Video expansion,
• Map generation and blanking,
• Adaptive area thresholding (CFAR),
• Correlation and validation of echoes,
• System Master clock for picture quality and stability.