AESA’s Advantages

By Ed McKenna | September 1, 2008
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The operational launch of the F-22 Raptor clearly signaled a changing of the guard for the United States fighter force. Bristling with advanced sensors and weapons systems, the fifth-generation Raptor, along with the F-35 Joint Strike Fighter, will take the lead in future war fighting efforts.

These new aircraft are also prompting a renewed retrofit focus on former generation fighters, including the addition of next-generation technologies to make many F/A-18, F-15 and F-16 fighters viable over the next two decades.

Critical to these upgrade efforts is Active Electronically Scanned Array (AESA) radar. This technology, which is standard on the fifth-generation aircraft, will become the sensor backbone for many of the earlier platforms. Lauded for its versatility, AESA radar also is being deployed on U.S. Coast Guard HC-130H surveillance aircraft and fighters destined for international customers.

Despite the operational and financial benefits, the campaign to outfit legacy fighters with AESA technology is running into some challenges, namely power, cooling and system costs.

AESA is the "latest and greatest (and) most desirable radar technology out there," said William Ostrove, electronics analyst for Forecast International, Newtown, Conn. The growth in AESA sales will help boost the worldwide radar market to $50 billion over the next 10 years, Ostrove said. Radars based on mechanically scanned arrays will still make up the bulk of the systems on the market, but the more expensive AESA units will account for a growing percentage of production over the decade.

AESA manufacturers, Raytheon and Northrop Grumman top Forecast International’s list of radar producers. There are also a number international consortia and companies involved, such as Selex Galileo, Thales and Israel Aerospace Industries.

Carving out a niche in the U.S. military market, AESA radar is also being sought by a number of countries that are purchasing aircraft, such as Singapore and United Arab Emirates. The Indian air force has made AESA radar a requirement in its Medium Multi-Role Combat Aircraft competition. That tender for 126 aircraft features a faceoff between six of the world’s leading fighter aircraft — the Lockheed Martin F-16, Boeing F/A-18E/F Super Hornet, Dassault Rafale, Mikoyan MiG-35 and Saab Gripen.

System Benefits

The demand for these new radar systems is largely driven by the significant performance improvements and increased reliability gained over legacy systems, according to industry and military officials. Generally, legacy systems rely on mechanically driven antennas that move back and forth to scan. An AESA antenna, on the other hand, does not move but rather consists of a matrix of small, solid state transmit/receive (T/R) modules, in which timing differences between the signals at each module are used to form and steer the radar beam.

On a practical level, the AESA radar "will register a 40 percent savings in life cycle costs over the legacy systems," said Patrick Geraghty, executive vice president radar systems, with Selex Sensors and Airborne Systems U.S. When you replace "the central traveling wave tube technology with a distributed multi-element array, you eliminate that single point of failure risk and get an inherent reliability increase," Geraghty said.

Also, the AESA antenna "has a gradual degradation," said Bill McHenry, Lockheed Martin F-16 business development director. There is no single antenna, but "hundreds of T/R modules, and if you lose one you still have (many) left." If you monitor the situation, "you can plan your maintenance and repairs (and) still fly the airplane and perform your missions."

Reliability was a key selling point for the U.S. Coast Guard when it tapped the Selex Seaspray 7500E AESA surveillance radar to replace the mechanically scanned Raytheon APS-137 on 16 of its HC-130Hs. The APS-137 has been "a very capable radar," but the system’s wave guides are "failing about every 80 hours," said Capt. Douglas Menders, aviation program manager, U.S. Coast Guard Aviation Acquisition.

The 7500E prototype has been deployed on an HC-130H for more than a year and "really has yet to fail," Menders said. In that time, the system has racked up more than 450 hours of operation.

The Coast Guard AESA radars have about 300 T/R modules, fewer than fire control radars on fighter aircraft, which can have more than 1,000 modules. It is "what we call a partially filled array," Geraghty said.

The system, which costs less than the higher density radars, requires fewer modules "because it is surveillance related."

The 7500E technology was developed in European programs including the Airborne Multirole Solid State Active Array Radar and CAPTOR Active Electronically Scanning Array Radar, Geraghty said. SELEX also offers its Vixen 500E AESA radar for fighter aircraft and UAVs as well as fixed and light helicopters.

Slated to be deployed by late 2009, the Coast Guard radars will cost $49 million, Menders said.

While it was standalone acquisition, the AESA radar will fit nicely with the new cockpit avionics suite, including five or six multifunction displays, that the Coast Guard is planning for the HC-130H, he said. The aircraft — some which date back to the early 1980s — are projected to continue in service to at least 2027.

Operationally, AESA radar is expected to deliver a 2-to-3 times boost in performance, said Mike Henchey, Raytheon director of strategy and business development, Tactical Airborne Systems (TAS). The technology extends "the range at which you are able to detect a target" and, "because you’ve got many, many small radars (or T/R modules), updates the target’s position very, very quickly," said Geraghty.

AESA radar can "truly be a force multiplier," said Dave Goold, Raytheon’s business development director for the F-18. On a two-place Super Hornet with decoupled cockpit, for example, "you could have the front cockpit doing an air-to-air mission, while nearly simultaneously the aft cockpit is performing air-to-ground."

The radar "supports multiple radar modes that include real beam mapping, Synthetic Aperture Radar (SAR) mapping, sea surface search, ground moving target indication and tracking and air-to-air search and track," said Cmdr. A.J. McFarland, F⁄A-18 and EA-18G radar integrated product team military lead for the Navy.

"These modes can be interleaved and operated near-simultaneously, demonstrating a quantum leap in combat capability over our legacy radars."

The Navy plans to deploy 437 F/A-18 E/F and EA-18G Growlers — the latter an electronic attack version of the F/A-18F slated to replace the EA-6B Prowler. About 304 will be delivered off the line from Boeing, while 133 will be retrofitted with radars "procured directly from Raytheon on a schedule of roughly 20 per year," McFarland said.

In July, Raytheon delivered its 100th APG-79 AESA system to Boeing and the Navy for the F/A-18 and EA-18G.

The first unit to deploy F/A-18s with the AESA radar is VFA-22, the "Redcocks," from Naval Air Station (NAS) Lemoore in California. "They deployed aboard USS Ronald Reagan in May (and) are currently in the Western Pacific," McFarland said in July.

The VAQ-129 Electronic Attack Squadron at NAS Whidbey Island, Wash., is the first EA-18G squadron to deploy the radar.

System Challenges

For all its potential, AESA technology also provides challenges. Selex’s Seaspray system, for example, includes many more modes than the older system, and "those modes are pretty robust," said Menders. "There are a lot of different interfaces and target symbologies (involved), so there is going to be a pretty good learning curve for the operators."

"In many ways, aircrew workload will increase because the AESA radar is capable of providing much more information than previous radars could provide," said McFarland.

"However, the improved range of the AESA also provides the aircrew with exponentially better situational awareness, enabling them to make better informed tactical decisions sooner than they could using legacy radars."

Radar manufacturers have faced and continue to face development challenges.

"Weight, costs, electricity and cooling — those are the big challenges," especially in the retrofit of these technologies, said Richard Aboulafia, vice president of analysis at the Teal Group.

Eight years ago, the first generation array was deployed on the F-15C because it is a "bigger fighter with a real solid structure and it could carry some weight," said Henchey. In fact, the system was so much heavier than the mechanical systems "ballast had to be placed in the back of airplanes," he added.

Current systems weigh about half as much as earlier radars, or about the same as mechanical systems, and will continue to decrease as the AESA gets thinner, Henchey said. Eventually, the array will become flexible enough to mount in areas other than the nose "because the requirement for flat mounting space will be backed off." The radar will be able to be oriented in different directions and provide a broader perspective.

The U.S. Air Force plans to upgrade the radars in 177 F-15Cs and 224 F-15Es — the two models are slated to remain in the fleet through 2025 and 2035, respectively, Henchey said.

In the marketplace, weight, cooling and power issues helped drive Lockheed Martin to build the separate F-16 Block 60 to meet United Arab Emirates’ requirement for 80 aircraft with AESA technology. The airplanes required "some cooling and power upgrades or enhancements," said McHenry. The first aircraft with the Northrop Grumman AN/APG-80 was delivered to UAE in 2005.

Lockheed is looking at upgrading some of its F-16 Block 50 aircraft.

"We are cautiously optimistic that this is a doable do and won’t involve a significant modification to the airplane," McHenry said.

The optimism is based on two recently launched programs: Northrop Grumman’s Scalable Agile Beam Radar (SABR) and Raytheon’s Advanced Combat Radar (RACR). The two programs are targeted at F-16 retrofits at least in the short run.

SABR is designed specifically to address F-16 electrical and physical interfaces without modification and fit within currently defined power and cooling requirements, according to Northrop Grumman. SABR demonstration flights are planned for later this year on Northrop Grumman’s Sabreliner, which emulates the F-16 avionics suite and has been used for previous F-16 radar testing. The SABR program "is our investment toward maintaining the F-16’s combat capability," said Chris Sheppard, F-16 Sensor Systems Program Development manager.

Similarly, RACR, unveiled at the Farnborough Airshow in July, "is designed to work with existing aircraft power and cooling," Henchey said. The RACR system can be "dropped with minimal impact into to the airplane."

The programs also tout lower prices. In fact, all of the manufacturers say prices have been on the decline, and there is evidence in the market to support this. "As it is being produced more and more and technology is maturing, the price is starting to go down, which is further increasing demand" for the systems, Ostrove said.

"We have been running the program since the early 1990s and have been able to over that time evolve the costs down to the point where we can readily compete with the traditional mechanical systems," said Geraghty.

It is "not exactly dollar for dollar; but when you compare the cost of acquisition compared with the life cycle cost savings, it is a very compelling argument."

"AESA is one of those technologies that is emerging and is now becoming cost effective," said McHenry. "By 2020 or 2025… it will be an accepted part of fighter airplanes."

However, outside of the Indian competition, "I don’t have any other customer who has an RFI [request for information] or RFP [Request for Proposal] on the street that says an AESA is a requirement. But I do have customers that are interested in talking about it," McHenry said.

AESA Developed For Communications

A versatile technology, Active Electronically Scanned Array (AESA) radar is being developed as a base for high-speed communications. However, the initiative is running up against funding challenges that are thwarting its progress.

Spearheaded by L-3 Communications, the effort to deploy this communication capacity is being abetted by both Raytheon and Northrop Grumman. The goal is allow for speedy transmission of the mass of critical data gathered by advanced sensors on fighter aircraft to others that may need it on the ground or in the air.

"What we have done is modify one of the common data link waveforms and turned it into a waveform that enables data to be carried on a pulse carrier signal instead of traditional continuous wave carrier," said Bruce Carmichael, vice president of Air Force Programs with L-3 Communication Systems West, based in Salt Lake City.

This waveform, called the Radar Common Data Link (R-CDL) or Pulsed Common Data Link (P-CDL), has been developed and was successfully flight tested about a year ago, Carmichael said. In practical terms, the capability would be "a new mode for the radar — a communications mode of operation," said Carmichael.

The capability of that mode encompasses a range of potential operations, from one-way broadcasts to interleaved "fully duplexed" exchanges between two stations, said Dave Robbins, an engineering lead for R-CDL at L-3 Communications.

Raytheon has demonstrated the system can transmit data at rates of 274 megabytes a second — "a speed that starts to approach instantaneous," said Mike Henchey, Raytheon’s director of strategy and business development, Tactical Airborne Systems. It is a speed that easily eclipsed the current military standard. "If you are relying on a tactical data link like Link 16, it might take you close to an hour to get a 72-megabyte file off of the aircraft," said Carmichael. With R-CDL, that transmission "is a matter of 3 to 5 seconds," he said.

The system could be used to provide close air support or help take out surface-to-air missile sites, said Joe Nunes, program manager for the Northrop Grumman R-CDL team at L-3 Communications. "Our sources told us that once a SAM site knows it is painted it can move in as little as six minutes," so time is of the essence, Nunes said. R-CDL can also provide real-time battle damage assessment to decision makers on the ground for re-tasking.

As far as system development is concerned, "we have gone through the basic challenges — the next step is to integrate the capability on the aircraft themselves… along with the man-machine interfaces," Carmichael said.

However, to do this and keep the program team together, the initiative needs funding. "That is the biggest thing right now," Carmichael said. "Our team is in a funding gap, so it is hard to keep the team together and go ahead," said Nunes.

On the positive side, "it has been recognized as a requirement for the F-22, so that is a major step forward," said Carmichael. — Ed McKenna

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