The U.S. Air Force wants companies' insights on a replacement for the Air Route Surveillance Radar-4 (ARSR-4). Northrop Grumman [NOC] delivered more than 40 ARSR-4s in the 1990s for border and coastal air traffic surveillance. The ARSR-4s have a more than 250 mile range. "The government is planning the Air Route Surveillance Radar Replacement (ARSR-R) program to replace ARSR-4 systems across multiple fixed radar sites," according to a Thursday business notice from Air Force Life Cycle Management Center's electronic systems…