The Air Route Surveillance Radar is used by the United States Air Force and the Federal Aviation Administration to control airspace within and around the borders of the United States. The ARSR-4 is the FAA's most recent (late 80s, early 90s) addition to the "Long Range" series of radars, which are search radars with a range of at least . The Westinghouse system is solid state and has a range. In addition, the ARSR-4 features a "look down" capability that enables the radar to detect aircraft attempting to elude detection by flying at low altitudes, advanced clutter reduction via hardware and software post-processing, and enhanced poor-weather detection of aircraft. A Beacon system, the ATCBI-6M (a monopulse system), is installed along with each ARSR-4. However, since the ARSR-4 is a 3D rada