Worldwide, air traffic control (ATC) is facing an increasing number of major challenges. These include the continuing increase inner traffic; an increase in the variety of aircraft types to be controlled; an increase in the number of small, slow and uncooperative targets (previously, these were almost always birds, but micro-unmanned air vehicles have rapidly become a concern); clutter (interference) caused by wind farms; an increasing risk over the coming years of interference from the long-term evolution of fourth generation (4G) mobile/cell phone systems (these operate on frequencies right next to those of ATC radars); and a need for deployable radars in a civilian context, to be able to cover gaps when fixed radars are under maintenance.

Traditional ATC radars are two-dimensional systems: they see only direction and distance. Typically, today, ATC systems involve a primary radar, which detects aircraft actively, by sending out electronic pulses that are reflected back by the target, and what is called secondary radar, which relies on transmissions from transponders on the aircraft (height information is provided by the transponder signals received by these secondary radars). “Effectively, these are two independent sensors, which are coordinated and combined,” explains Airbus Defence and Space (DS) ATC and Identification Friend or Foe (IFF) Sensor Sales head Thorsten Oelgart. “The essential difference is, with secondary radar, you have a transponder aboard [the aircraft], which is actively interrogated by the secondary radar.”

An air traffic controller has “to keep flying objects apart. It’s quite a challenging job. It’s very, very stressful,” he points out. “You now have a huge variety of aircraft to handle, from ultralights to very large airliners and even very fast combat jets. Another, very new challenge is wind farm clutter. A wind turbine has a very nasty characteristic for ATC radar: it is high, with rotating blades, which makes it a big radar target; worse, the high speed of the blade tips create a doppler effect which makes the turbine appear as a moving target on the ATC radar – this is especially so when the turbine is not facing the radar antenna but is at an angle to it.”

Airbus DS states that all these problems and challenges are addressed by its latest ATC radar system, the ASR-NG, which combines proven military technologies with ATC requirements. (ASR stands for Airport Surveillance Radar and NG for Next Generation.) The ASR-NG antenna is fitted with three feed horns, which makes it unique among ATC radars. These horns are used in both the transmission and reception of radar signals, and mounting three on each antenna means that each radar can process three radar beams. This makes it the first three-dimensional ATC radar in the world (that is, it can measure height as well as direction and distance). Three-dimensional radars have been used by armed forces for air defence for many years now, but ATC has lagged far behind, because such sophisticated radars were not thought necessary for civil ATC work. This has now changed, thanks to the growing number of uncooperative targets and wind farms, which require more sophisticated technology to handle.

The ASR-NG also provides another advantage: greater range. It has a range of up to 120 nautical miles, at which range it can detect targets with a radar cross section of 2 m2. This means that it can fulfil the role of both an airport approach radar and a medium-range air surveillance radar. “This is double the range of a normal ATC radar,” he highlights. “We already have two customers.” Both customers are using the ASR-NG to replace both their current surveillance and approach radars, so replacing two systems with one, with obvious economies on training, servicing and support.

It operates in the S-band frequency range (2 GHz to 4 GHz; frequencies for radar start at 2.7 GHz, while 4G mobile telephone frequencies end at 2.69 GHz) but is immune to interference from 4G telecommunications systems, both now and in the future. “We have also proven the wind power mitigation of the radar,” notes Oelgart. This has been successfully demonstrated with offshore wind farms in the UK, in tests involving 102 wind turbines mounted on 118-m-high pylons. These tests were observed and independently reviewed by the British Ministry of Defence. The ARS-NG also neutralises ground clutter (interference caused by radar pulses hitting the ground, hills, buildings and being reflected back to the antenna). The system’s electronics, including the processors, can be installed in a building or in a movable shelter. A deployable version of the radar is available, which can be used to cover gaps created by maintenance of fixed radars at airports. A military ATC version of the radar is also available (it is resistant to jamming and can process military IFF signals).