En-Route Radar
Figure 1: The antenna of the En-Route Radar SRE-M6 in Nordholz, Germany
En-Route Radar
En-Route Radar is a special type of air traffic control radar developed for en-route control of airspace. It can be used to monitor air traffic outside the special control areas near airfields.
These radars normally operate in the L-band with a maximum range of up to 240 NM (≙ 450 km). They are primary radars, which usually only provide a two-dimensional view of the airspace for cost reasons. However, they are always coupled with a modern Mode S capable secondary radar, which then provides the third spatial coordinate.
In most cases, the antenna is a parabolic reflector antenna and scans the airspace with an antenna pattern with cosecant squared characteristics. More rarely a planar array antenna is also used (see Figure 2). The antennas rotate relatively slowly at a speed of 4 to 6 revolutions per minute. This speed of rotation results from the temporal conditions that such relatively long ranges bring with them. Depending on the projected range, these En-Route Radars are installed on a more or less high tower to counteract the limitation of the range at lower altitudes due to the curvature of the earth. In unfavorable climatic conditions, the antennas are installed under a protective radome.
Figure 2: The robust antenna of the ATCR-44S does not require a radome
In Germany, there are a total of six such en-route radars operated by the Deutsche Flugsicherung GmbH (DFS). Each of these six stations has a range of about 145 NM (≙ 270 km). They are useed remotely from the radar control centers in the respective area. For example, the En-Route Radar in Nordholz of type SRE-M6 is remotely controlled from the radar control center at Bremen Airport (“Bremen Control”) and monitors the north-west of Germany and the entire North Sea.
Air traffic controllers in the radar control center also provide air traffic control services for many smaller airports without radar services, for example, to clear take-off or to clear an approach to the airport. For this reason, en-route radars should also have a good low-altitude coverage.