The AN/APQ-181 is an all-weather, stealthy radar which operates in the Ku band. It was developed by Hughes Aircraft in the 1980s for the US Air Force and is used on B-2A Spirit bomber aircraft, entering service in 1993. The AN/APQ-181 is a low probability of intercept radar which enables the unique combination of stealth, range, payload, and precision weapons delivery capabilities. The radar, which is today manufactured by Raytheon, features a number of precision targeting modes, and also supports terrain following and terrain avoidance. The original design consists of a TWT-based transmitter with a 2-dimensional passive electronically scanned array (PESA) antenna.
As part of the radar modernization program (RMP), Raytheon has designed, built and delivered an active array, based upon an advanced T/R module design offering improved performance and reliability. The RMP is currently in flight testing of the new antenna and will enter production in summer 2007, which will replace all the electronically scanned arrays currently in the fleet with the new active arrays. The new Active Electronically Scanned Array (AESA) provides the stepping stone to additional future radar enhancements. In 2002, Raytheon was awarded a contract to develop a new, Active Electronically Scanned Array (AESA) version of the APQ-181. This upgrade will improve system reliability, and will also eliminate potential conflicts in frequency usage between the B-2 and commercial satellite systems that also use the J band.