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| Northrop Grumman, L-3 Turn F/A-22 Radar Into Wide-Bandwidth Data Link |
| By David A. Fulghum |
| 12/11/2005 07:09:18 PM |
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 TALKING RADARS New radars are becoming sophisticated radios--radios that can be used as weapons against insurgents. A series of experiments is turning the radars of next-generation tactical aircraft--including the F/A-22 and F-35--into advanced communications devices for intelligence-gathering, reconnaissance and strike missions. Laboratory tests by Northrop Grumman and L-3 Communications researchers show new active electronically scanned array (AESA) radars can be modified to send and receive large amounts of information at high data rates. So new-generation fighters not only should be able to collect large amounts of intelligence and targeting data, but also may be able to whip those large packages of information around the battlefield in seconds instead of tens of minutes required by current data links. These tests add communications as yet another role for the AESA radar that is already being pitched as a multifaceted surveillance device, electronic jammer and directed-energy weapon (AW&ST Sept. 5, p. 50). It also means that the F/A-22 aircraft will immediately have a key role in network-centric warfare and in the future could be able to affect enemy communications by collecting their signals and inserting false or confusing data into those networks as the forward-most elements in an information war. While not part of this test program, Air Force planners expect to use the stealth aircraft's very sensitive and extensive receiver arrays to both gather and exploit electronic and communications intelligence. Some companies are already eyeing worms, viruses and other algorithms as cyber-weapons that can be released by stealthy manned and unmanned aircraft that can penetrate air defenses to monitor enemy electronic activity at close range (AW&ST Oct. 24, p. 49). The company wants to conduct flight demonstrations within 12 months on a corporate test aircraft, says Joseph J. Ensor, vice president of combat avionics for Northrop Grumman Electronic Systems. Using company research and development money, scientists demonstrated high-data-rate, broadband communications using the AESA radar designed for the F/A-22. They say the capability-- primarily the result of waveform and software modifications, not hardware changes--can be made to virtually any AESA radar. For the testing, an F/A-22, third-generation APG-77 radar is linked to an L-3 software programmable modem that turns the AESA on low-observable aircraft into a data link without disturbing the stealth fighter's signature, says Bruce Carmichael, L-3's vice president of Air Force programs. Air Force officials have emphasized that they want to exploit the fact they can get close to sensitive targets to both avoid detection and pick up low-power electronic signals. One target set includes hand-held, wireless communications devices. "I don't see why we couldn't take something [collected] from another sensor and run it through this aperture," says Ensor. "We're taking what's in the cockpit and making it available for the whole battlefield. As long as we can get it to the right place in the jet, we can move any data offboard. It doesn't have to be data we collected." Carmichael agrees. "From the communications standpoint, data is data. We don't really care." Researchers have already demonstrated the transfer of a 72-megabyte synthetic aperture radar image in 3.5 sec. at a data rate of 274 Mbps., Carmichael says. By comparison, it would take 48 min. on today's standard Link 16. He says they ultimately demonstrated transmission rates in the laboratory of 548 Mbps. and receive data rates of up to 1 Gbps. through the F/A-22 radar array. THE L-3 PACKAGE involves an unnamed software programmable modem. Future tests of the capability will involve modems being developed for the Air Force Research Laboratory including derivatives of the Multi-Platform CDL. "There is not a big solution set out there that satisfies all the high data rates that are demanded by some of the hardware," Ensor says. "So we teamed up with L-3 and put together our corporate IRAD money and looked at an approach . . . to turn the AESA into a data link and create a dual-purpose aperture on the airplane. We were able to demonstrate two-way communications using a modified CDL [Radar Common Data Link] waveform [that could] provide the warfighter an unprecedented data stream." Today, CDL is the primary means of transmitting sensor data in terms of wideband communications, says Carmichael. L-3 is using technology it developed in building wideband data links for the U-2 and Global Hawk to put a similar capability on advanced fighters that would allow them to transfer large files generated by an array of sophisticated sensors. "Typically you would hang a directional aperture off the platform to achieve high data rates so that you're not spending a long time downloading data off a platform," he says. "You [already] have a great aperture on the new aircraft. Let's use that to get very high-capacity communications off the aircraft." The effort has been successful enough to attract the interest of Air Combat Command, a necessary step in changing the effort from a company initiative to a program of record for the U.S. Air Force and, probably, the Navy (which flies similar radars on its F/A-18E/F strike aircraft and, soon, on its fleet of EA-18G Growler electronic attack aircraft). USAF planners also are considering the capability for modernization of F-16s, a number of F-15C interceptors and F-15E strike aircraft. Moreover, while the initial testing looks at AESA radar arrays on smaller tactical aircraft, there's also the potential that large arrays--such as the MP-RTIP radars planned for the Global Hawk unmanned reconnaissance aircraft and E-10 multi-sensor command-and-control aircraft (or an E-8 Joint Stars upgrade)--could pass even more information at higher rates. "IF YOU HAVE MP-RTIP out there collecting data, they'll be able to share it more quickly with the fighter-strike guys," says Scott L. Porter, director of aerospace systems marketing. In fact, larger arrays like the 21 X 4-ft. MP-RTIP may allow even faster data rates. "Definitely, that's part of the physics equation; power and aperture size are the major considerations," says Carmichael. A note of caution is interjected by Ensor, who says they've yet to establish where efficiency begins to fall off as the size of a sensor antenna increases. Nonetheless, "this is a capability that we could bring to almost any AESA radar," he says. "While we haven't looked at the architectural pieces that would make up that functionality yet, I believe we could bring that technology to MP-RTIP." If there is an advantage to larger arrays, it could mean a huge data pipeline is available to those surveillance aircraft that are dedicated to collecting and transferring massive amounts of imagery for analyses, often to sites halfway around the world. AESA radars are made of hundreds or thousands of small transmitter/receiver elements that can be used for many separate tasks (such as searching, tracking, communications) or focused to find small targets (such as low-signature cruise missiles) or, in the future, to create a pulse of energy that could upset the guidance or other electronics of enemy missiles. "For this test we used the entire array [of T/R elements in the radar, a classified number]," Carmichael says. "That doesn't mean in another scenario we couldn't use the elements differently," Ensor adds. "It's a maturation process. Our goal was just to prove we could do the first step--to transmit a large SAR map using a modified data link algorithm to get it offboard and to do bidirectional transmissions. One of the things that brought us to the conclusion of using this as a communications antenna is that obviously there are a limited number of apertures on the airplane and all the real estate is taken. So, we're looking for multiple uses of the apertures. We thought this lent itself very well to line-of-sight coms because we have the big power aperture and can send the imagery a long way. What happens when you build a big SAR map? Traditionally you have to wait until you land. We're looking at getting it off the platform in near real time." For the immediate future, the role of the radar as a communications device would focus on classic reconnaissance and the sending of images to other aircraft, ground units, air operations centers and intelligence exploitation centers. The aircraft also would be able to conduct real-time bomb-damage assessment within seconds of a strike mission.
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