F-15s Looking for the AESA Edge


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Jun 8, 2009
F-15s Looking for the AESA Edge

F-15C Eagle air superiority fighters have traditionally used APG-63 radars with mechanically steered arrays. While upgrades over the years have improved them, the mechanical steering components are a point of potential failure given the stresses put on them, and better radar technologies have appeared. With cruise missile defense rising in importance, and longer-range detection of threats desired, upgrades are necessary. They may also correct a known air-air weakness that can reputedly be exploited by aircraft like Russia’s SU-30 family, though other reports claim that the mechanically-scanned APG-63v1s have also worked to close that hole. Thus far, 18 USAF F-15Cs have been modified to carry APG-63v2 radars – a misnomer, since the upgrade uses a revolutionary new AESA technology that bears little resemblance to its predecessor.

The USAF is discussing a retrofit set that would turn the F-15Cs into multi-role fighters; an AESA radar will be part of that, and the program to equip select F-15C units with AESA radars as an air-air improvement continues. They will now be joined by the USAF’s entire 2-seat, multi-role F-15E Strike Eagle fleet, whose future AESA radar just received some improvements, and a new designation…

The USAF’s F-15C air superiority fighters have traditionally used APG-63 pulse-Doppler radars with mechanically steered arrays. Almost 1,000 APG-63s had been delivered when production ended in 1986, and about 700 are still operational in F-15As, Bs, and early model Cs and Ds operated by the U.S. Air Force and the air forces of Israel, Japan, and Saudi Arabia.

The multi-mode AN/APG-70 mechanically-scanned array radar is a 1980s derivative of the APG-63 that adds air-ground modes and maintainability improvements. Gate array technology adds air-ground modes, and improve air-air effectiveness as well. The APG-70 is employed on late model F-15C/D Eagles, all F-15E Strike Eagle aircraft, and on the Israeli F-15I and Saudi F15S Strike Eagle variants. A variant of the APG-70 radar called the AN/APQ-180 adds a modified planar array, an upgraded signal processor, and several enhanced air-to-ground modes. It is used on the USA’s AC-130U Specter gunship aircraft.

The AN/APG-63v1 is a 1990s reliability/ maintainability upgrade that adds modern hardware with opportunities for capability growth, and enhances air-air and air-ground capabilities. It is NOT an AESA radar. Raytheon has received 5 production orders to deliver 161 APG-63(V)1 radar systems plus spares to the US Air Force, and the first units entered service in March 2001. Up to 170 may be ordered. Another 40+ radar systems and spares will be delivered to Korea for their F-15K. Some Japanese F-15Js have also been fitted with a license-produced Mitsubishi Electric (Melco) APG-63v1 as a first step toward a general fleet upgrade.

n contrast, Active Electronically-Scanned Array (AESA) radars are made of hundreds or thousands of small transmitter/receiver (TR) elements. Moving parts are eliminated; instead, subsets of their array elements are used to focus on each task very quickly and precisely, without having to move them physically, and with little signal “leakage” outside of its focused beams. This makes them more reliable, more powerful, and able to operate in multiple modes at once. There’s also a maintenance advantage. A partial failure in previous radars renders them unfit for use, but AESA radars only suffer a slight performance drop if some of their TR modules fail. The fighter can still fly as it awaits a fix, enjoying all of the radar’s simul-mode, range, focusing, low “leakage,” and communications benefits. AESA radars have taken a while to enter widespread service on fighter aircraft because the cost of each array had to come down to an affordable level, but once that happened their advantages become compelling.

Raytheon’s AN/APG-63v2 was the world’s first AESA radar system to be operationally deployed in a fighter aircraft, entering service with the F-15Cs at Elmendorf Air Force Base, Alaska in December 2000. At present, 18 operational F-15Cs fly with the APG-63v2 radar, and a 19th F-15C has been equipped with the APG-63v3 for testing purposes. Current plans call for up to 48 more APG-63v3-equipped F-15Cs, but some options under discussion could grow that number.

The Raytheon APG-63v3 AESA radar combines APG-63v2 AESA software with the hardware advances that went into the F/A-18 E/F Super Hornet Block II’s AN/APG-79 AESA radar. Whereas the AP-63v2 AESA had a square profile, the APG-63v3 can be recognized by the rounder shape of its array. It uses lighter and more advanced AESA technologies that include a tile array arrangement, and a new processor.

The ‘v3’ is being fitted to F-15C aircraft as an extension of earlier air-air upgrades, and has now been picked to equip the USAF’s F-15E Radar Modernization Program (RMP), beating Northrop Grumman’s offer of the AN/APG-77v1 radar that equips the F-22A Block 20. Singapore’s new F-15SG Strike Eagles will also use the APG-63v3 radar, and Japan has reportedly expressed interest in it as a fleet upgrade possibility for its F-15J (F-15 C/D equivalents).

The F-15E RMP’s fit-out would later add a few refinements, and receive a new designation. New Radio Frequency Tunable Filters (RFTF) will enable the aircraft’s radar and Electronic Warfare System to function at the same time, and an improved Environmental Cooling System (ECS) will improve liquid cooling capacity 250% percent. A new wideband radar radome completes the major modifications, and the radar will be designated APG-82v1.

F-15s Looking for the AESA Edge

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