Experiences in the Vietnam War revealed the need for air superiority fighters and better air-to-air training for fighter pilots. Based on his experiences in the Korean War and as a fighter tactics instructor in the early 1960s Colonel John Boyd with mathematician Thomas Christie developed the Energymaneuverability theory to model a fighter aircraft's performance in combat. Boyd's work called for a small, lightweight aircraft that could maneuver with the minimum possible energy loss, and which also incorporated an increased thrust-to-weight ratio. In the late 1960s, Boyd gathered a group of like-minded innovators that became known as the Fighter Mafia and in 1969 they secured Department of Defense funding for General Dynamics and Northrop to study design concepts based on the theory.
Air Force F-X proponents remained hostile to the concept because they perceived it as a threat to the F-15 program. However, the Air Force's leadership understood that its budget would not allow it to purchase enough F-15 aircraft to satisfy all of its missions. The Advanced Day Fighter concept, renamed F-XX, gained civilian political support under the reform-minded Deputy Secretary of Defense David Packard, who favored the idea of competitive prototyping. As a result, in May 1971, the Air Force Prototype Study Group was established, with Boyd a key member, and two of its six proposals would be funded, one being the Lightweight Fighter (LWF). The Request for Proposals issued on 6 January 1972 called for a 20,000-pound (9,100 kg) class air-to-air day fighter with a good turn rate, acceleration and range, and optimized for combat at speeds of Mach 0.61.6 and altitudes of 30,00040,000 feet (9,10012,000 m). This was the region where USAF studies predicted most future air combat would occur. The anticipated average flyaway cost of a production version was $3 million. This production plan, though, was only notional as the USAF had no firm plans to procure the winner.
The F-16A/B was originally equipped with the Westinghouse AN/APG-66 fire-control radar. Its slotted planar array antenna was designed to be compact to fit into the F-16's relatively small nose. In uplook mode, the APG-66 uses a low pulse-repetition frequency (PRF) for medium- and high-altitude target detection in a low-clutter environment, and in look-down/shoot-down employs a medium PRF for heavy clutter environments. It has four operating frequencies within the X band, and provides four air-to-air and seven air-to-ground operating modes for combat, even at night or in bad weather. The Block 15's APG-66(V)2 model added a more powerful signal processing, higher output power, improved reliability and increased range in cluttered or jamming environments. The Mid-Life Update (MLU) program introduced a new model, APG-66(V)2A, which features higher speed and more memory.
The AN/APG-68, an evolution of the APG-66, was introduced with the F-16C/D Block 25. The APG-68 has greater range and resolution, as well as 25 operating modes, including ground-mapping, Doppler beam-sharpening, ground moving target indication, sea target, and track while scan (TWS) for up to 10 targets. The Block 40/42's APG-68(V)1 model added full compatibility with Lockheed Martin Low-Altitude Navigation and Targeting Infra-Red for Night (LANTIRN) pods, and a high-PRF pulse-Doppler track mode to provide continuous-wave radar (CW) target illumination for semi-active radar-homing (SARH) missiles like the AIM-7 Sparrow. Block 50/52 F-16s initially used the more reliable APG-68(V)5 which has a programmable signal processor employing Very-High-Speed Integrated Circuit (VHSIC) technology. The Advanced Block 50/52 (or 50+/52+) are equipped with the APG-68(V)9 radar, with a 30% greater air-to-air detection range and a synthetic aperture radar (SAR) mode for high-resolution mapping and target detection-recognition. In August 2004, Northrop Grumman were contracted to upgrade the APG-68 radars of Block 40/42/50/52 aircraft to the (V)10 standard, providing all-weather autonomous detection and targeting for Global Positioning System (GPS)-aided precision weapons, SAR mapping and terrain-following radar (TF) modes, as well as interleaving of all modes.
The F-16E/F is outfitted with Northrop Grumman's AN/APG-80 active electronically scanned array (AESA) radar. Northrop Grumman developed the latest AESA radar upgrade for the F-16 (selected for USAF and Taiwan Air Force F-16 upgrades), named the Scalable Agile Beam Radar (SABR). In July 2007, Raytheon announced that it was developing a Next Generation Radar (RANGR) based on its earlier AN/APG-79 AESA radar as a competitor to Northrop Grumman's AN/APG-68 and AN/APG-80 for the F-16.