AN/APQ-181 Radar System
The light surface below the wing edges is the AN/APQ-181 radar antenna.
The AN/APQ-181 is an advanced all-weather, low probability of intercept (LPI) phased array radar system, designed specifically for the B-2A Spirit stealth bomber by Hughes Aircraft Company (now part of Raytheon). Developed during the 1980s, the radar entered operational service in 1993. Known for its precision targeting capabilities and advanced terrain-following and terrain-avoidance features, the AN/APQ-181 has been a cornerstone of the B-2’s mission capability.
Design and Functionality
AN/APQ-181 (© 2012 Raytheon)
Initial Design
The AN/APQ-181 was developed to provide superior stealth capabilities through its low probability of intercept (LPI) radar emissions, making it difficult for adversaries to detect the radar signals. Key features include:
- Terrain-following radar: Allows the B-2 to fly at low altitudes, avoiding enemy radar detection.
- Terrain avoidance: Ensures the aircraft avoids obstacles during missions.
- Precision targeting: Enables accurate strikes on designated targets in all weather conditions.
The radar operates in the Ku band, which is part of the J band frequency range, and originally used a two-dimensional passive electronically scanned array (PESA) antenna with a traveling wave tube (TWT)-based transmitter for signal generation.
Recognition and Impact
The AN/APQ-181 was a key technological innovation integrated into the B-2 program. In 1991, the B-2 Industrial Team, including Hughes Aircraft, received the prestigious Collier Trophy for the development, production, and flight testing of the B-2 aircraft. This award recognized the program’s significant contributions to the advancement of aerospace technology and U.S. national security.
Upgrades and Modernization
Transition to AESA Technology
In 2002, Raytheon began work on an upgraded version of the AN/APQ-181 radar, transitioning it to active electronically scanned array (AESA) technology. The AESA upgrade offered several advantages, including:
- Improved reliability: Reduced maintenance requirements and extended operational life.
- Frequency deconfliction: Mitigated interference with commercial satellite systems operating in the J band.
Cost and Implementation Challenges
In 2008, a significant challenge emerged when the Federal Communications Commission (FCC) inadvertently auctioned off part of the radar’s operating frequency spectrum to a commercial user. This necessitated further upgrades to the radar at an estimated cost of over $1 billion.
By 2010, all B-2 aircraft were expected to have the new AESA-equipped radar system installed, ensuring compliance with updated frequency regulations and maintaining operational effectiveness.
Conclusion
The AN/APQ-181 radar system remains a critical component of the B-2A Spirit’s advanced stealth and precision strike capabilities. Through its initial design and subsequent AESA upgrade, the radar exemplifies the integration of cutting-edge technology to meet evolving mission demands and regulatory challenges.
References
- “Radar System Developments for the B-2 Spirit,” Federal Aviation Archive, 2008.
- U.S. Air Force Fact Sheet: AN/APQ-181 Radar Overview.
- Collier Trophy Archives, National Aeronautic Association.
- Raytheon Company Press Releases, 2002 and 2010.
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