The B-2 carries a Lockheed Martin radar warning receiver, a Northrop Grumman defensive aids system and the Lockheed Martin AN/APR-50 defensive management system (DMS).

Section Airborne electronic warfare (EW) systems

TypeAirborne Electronic Counter Measures (ECM), Electronic Support Measures(ESM) and Radar Warning Receiver (RWR) system.

Description AN/APR-50 Defensive Management System (DMS) is installed in USAF B-2aircraft. The system is classified and very few technical details have been released. It is believed that the system is designed to present aircrew with intercepted emitter information overlaid on a pre-programmed display of known emitter locations. The installation features a number of antennas, distributed all around the airframe, feeding nine radiofrequency front ends, which detect and analyse a wide variety of signals. Each of these front ends may be tuned to a different part of the frequency spectrum. Five receivers take the outputs of the front ends and pass them to the processor. There is considerable speculation that the AN/APR-50 utilises an ECM technique known as ’active cancellation’ - this stealth technique employs an array of antennas to transmit a signal which is out of phase with incoming radar emissions, thus effectively reducing the intensity of the reflected returns through interference. If the emitted interference signal, travelling in the same direction, is exactly matched in terms of amplitude, period and phase, to the reflected radar signal, then the threat radar would not be able to detect any return signal, thus failing to ’see’ the aircraft. This is called destructive interference. In terms of applying such ECM techniques to an airborne platform, incoming signals will have many different characteristics of amplitude, period and phase, which, combined with the many different directions of reflection, resulting in phase/amplitude shift, will make true ’cancellation’ extremely difficult to achieve in the real world. It is more likely that the characteristics of the strongest incident signal would be selected by the system processor for destructive interference. Operational status The Northrop Grumman Company designation of the system is ZSR-63. January 1993, Northrop Grumman was awarded a US$117 million contract to continue the development of the AN/APR-50. Northrop Grumman was also awardedUS$53.9 million to carry on with ESM development, including the extension of the frequency range. It is believed that this was originally for Band 2and the extension was to cover Band 4 from 500 MHz to 1 GHz. While it is believed that baseline versions of the system failed to meet operational expectations, software changes completed during the second quarter of 1998were incorporated to address these problems. AN/APR-50 systems installed in Block 30 aircraft are described as ’fully capable in Bands 1 to 4’.Additional software upgrades were implemented during 2001-2002.