Elec Tricks: Turning AESA Radars Into Broadband Comlinks
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The F/A-22 and F-35‘s advanced built-in radars and electronics can be levered to turn these planes into electronic warfare aircraft. Meanwhile, some of the key trends in military I/O highlight the increasing need for high-bandwidth links. That need is biting with equal or greater force between aircraft, and between aircraft and other platforms, as the increasingly rich array of combat data available finds itself constricted by older protocols and low-bandwidth linkages.
As it turns out, the solution may have been sitting right under their noses.
The Concept
Aviation Week & Space Technology reports that Northrop Grumman and L-3 Communications came up with an interesting finding while doing private research in this area: active electronically scanned array (AESA) radars can also be modified to send and receive large amounts of information at high data rates.
While the demonstration was done using the F/A-22’s ultra-advanced 1,500+ element AN/APG-77 radar, the engineers involved say the idea should work with any AESA radar (the F-15C/SG’s new APG-63v2/3, the F/A-18 E/F Super Hornet and EA-18G Growler‘s APG-79, the F-16 E/F Block 60’s new APG-80, or the F-35 JSF Lightning II’s APG-81). The system may even get increased bandwidth from bigger AESA radars like the MP-RTIP radars planned for the RQ-4 Global Hawk and some new AWACS (Airborne early Warning And Control Systems) and ELINT/SIGINT(Electronic/Signals Intelligence collection) planes. Unsurprisingly, US Air Combat Command is very interested. So, how does this work?
The AESA Edge
AESA radars are made of hundreds or thousands of small transmitter/receiver elements that can be used for many separate tasks. They’ve taken a while to enter service because the cost of each array had to come down to an affordable level, but once that happened their lack of moving parts and ability to electronically “steer” subsets of their array elements to focus on their tasks made them highly desirable. As Dr. Carlo Kopp explains:
“An electronically steered antenna… is designed with an individually electronically controlled device behind each antenna element, which can manipulate the time delay or phase of the microwave signal passing through it. With a computer controlling each element in unison, the beam direction and its shape could be digitally controlled, within a matter of milliseconds or tens of milliseconds.
…The basic building block of any AESA is the Transmit Receive Module or TR Module. It is a self contained package making up one AESA antenna element, and contains a low noise receiver, power amplifier, and digitally controlled phase/delay and gain elements. Digital control of the module transmit/receive gain and timing permits the design of an antenna with not only beam steering agility, but also extremely low sidelobes in comparison with passive ESA and mechanically steered antennas.”
In other words, AESA focuses individual elements very quickly and precisely, without having to move them physically, and with little signal “leakage” outside of its focused beam. This makes it reliable, powerful, and able to “timeshare” by switching from mode to mode fast enough that multiple modes can effectively be operating at once. When DID covered the F/A-18 Super Hornet’s AN/APG-79 AESA radar, for instance, we noted its revolutionary ability to conduct simultaneous air-to-air and air-to-surface radar scans, without having to be switched from one to the other.
All of these capabilities are highly relevant to the task of moving large amounts of data. Why not “focus” coded data signals through the radar’s aperture, as long as the party on the other end can receive and interpret them? The AESA’s ability to focus almost instantly puts it on target fast enough, its low-leakage beam focus lowers the risk that it will disturb the aircraft stealth “signature,” the radar’s power and sensitivity should make it a good platform, and its ability to timeshare means that communication won’t disturb its other functions.
So, why not add a send and receive twist that communicates information to a properly prepared party, instead of just bouncing signals off of other things?
The Tests
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For the testing, the F-22 Raptor’s AN/APG-77 radar was linked to an L-3 Communications modem. The modem is software-programmable, which means it can be adapted to send and receive using various protocols (“waveforms”). For the test, they used a modified CDL [Radar Common Data Link] waveform, and the entire array of elements in the radar. They then demonstrated the transfer of a 72 MB synthetic aperture radar image in 3.5 seconds at a data rate of 274 Mbps. That would have taken 48 minutes using Link 16, which is the standard data exchange system in US and allied equipment. In practice, that means the sensor data is downloaded and communicated only when the plane lands.
What if that sort of thing could happen in near-real time instead?
Aviation Week reports that the researchers eventually demonstrated lab transmission rates of 548 Mbps, and receive data rates of up to 1 Gbps.
The Implications
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If data rates in real-life conditions can even approach those numbers, bye-bye bandwidth bottlenecks. Because the capability is mostly dependent on waveform and software modifications that use a pre-existing capability in a different way, any AESA radar should be able to do it.
The reason this development becomes particularly exciting in conjunction with the F/A-22 Raptor and F-35 Joint Strike Fighter is that both of these planes have a unique feature – they have many different kinds of sensors and antennas embedded all over the aircraft, opening up potential electronic intelligence collection and electronic warfare roles.
The thing about all those sensors, however, is that lots of sensors generate lots of data. The aircraft need the advanced computers they’ve been given to make sense of it all – in the F-22’s case, it’s the equivalent of 2 Cray supercomputers, with significant room for expansion. Even the synthesized picture presented to the pilot will be a “big data” picture.
With older methods like Link-16, aircraft could be forced to share very abridged forms of that data. With AESA/CDL transmission, however, the ideal of “what one pilot knows, they all know” can become much more of a reality. The data can also be fired back to high-flying UAVs, AWACS planes, ground stations, et. al. for rapid transmission to other air, ground, or command assets.
As one of the researchers put it:
“I don’t see why we couldn’t take something [collected] from another sensor and run it through this aperture… 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.”
Now, here’s the next question. If the effectiveness and bandwidth you can send corresponds to power and the number of array elements used, then larger AESA radars with more elements and more power feeding them should be able to create more send and receive bandwidth. The question is where one starts to reach a point of diminishing returns, and that’s a subject the researchers haven’t quite delved into yet.
The effort has apparently been successful enough to attract the interest of US Air Combat Command, however, which could allow the program to move from a private research effort to an official program of the US Air Force. Not to mention the US Navy, which operates AESA radars of its own.
AESA radars are a technology segment where the USA has a significant edge over all rivals – and if this research pans out, the resulting advantages for US forces could be at least as significant.
Contracts & Key Events
June 13/07: Northrop Grumman Corp. and its teammates L-3 Communications, Inc. and Lockheed Martin Corp. have successfully conducted the first in-flight communication’s link with an active electronically scanned array (AESA) radar. Using off-the-shelf, L-3 programmable modems and a new R-CDL waveform, the Radar Common Data Link (R-CDL) used the AESA radar’s fire control transmitter and antenna to perform high-data rate, two-way communications, streaming synthetic aperture radar map imagery and streaming video from a Northrop Grumman BAC 1-11 test aircraft to an L-3 Communications ground station. During the mission, the team transmitted and received in full duplex at 274-megabits per second burst rate. NGC release.
Jan 11/07: A Raytheon release said that efforts “to design and develop the next-generation wideband common data link for active electronically scanned array radar systems [under] The Radar Common Data Link program…” and adds that “The five-year program calls for Raytheon to develop specifications and open-standards interfaces for a radar common data link to determine how it would operate with current and future AESA systems, to formulate concepts of operations with the Air Force, and to demonstrate feasibility.”
Raytheon is teamed with L-3 Communications (experience with common data link waveforms) and Boeing (platform partner for integration of the AESA technology on the F-15 and F/A-18 aircraft) on the program; no mention of Northrop Grumman. At this time, $1.6 million has been obligated. Solicitations began June 2006, negotiations were complete October 2006, and work will be complete in October 2011. The Air Force Research Laboratory at Wright-Patterson Air Force Base, OH issued the contract. (FA8F650-07-D-4502).
Oct 17/06: Raytheon Co. in El Segundo, CA receives a $9.7 million indefinite delivery/indefinite quantity, cost-plus-fixed-fee contract:
“This effort will determine the technical feasibility of using radar apertures/systems as a data link to transmit synthetic aperture radar data (and other data types) using a modified common data link waveform (or equivalent) in near real time. The demonstration will occur in three phases. A phased approach will be used to reduce technical, cost and schedule risk by demonstrating technical feasibility prior to awarding any further task orders.”
Additional Readings and Sources
- Northrop Grumman – AESA Radar: Revolutionary Capabilities For Multiple Missions [PDF]. Details a number of the radar type’s characteristics that make it special, and offers insights into some of the developments within the AESA field.
- Raytheon – Raytheon’s Revolutionary AESA Technology. Includes links to their various AESA radar designs and capabilities, and adds as a list of related press releases at the bottom.
- DID (Dec 18/05) – AESA Comlinks: DID Reader Has Done Prior Research. Dr. Carlo Kopp has already done a fair bit of work in the field, beginning with his PhD thesis in Melbourne in 1999. He has some insights into the hard parts ahead for Northrop-Grumman and L-3, and would be happy to share. Read the article for an outline and links to more in-depth materials.
- DID FOCUS Article – The Wonders of Link 16 For Less: MIDS-LVTs (updated). MIDS-LVT is a very popular way of getting Link-16 capability into aircraft, and other variants are installed on ground or naval platforms. The Swiss, with mountains that can disturb other communications, are even installing a Link-16 network that will cover their whole country.
- Aviation Week & Space Technology (Dec 11/05) – Talking Radars
- DID (Oct 24/05) – Supersonic SIGINT: Will F-35, F-22 Also Play EW Role?
- DID (Sept 9/05) – Military Avionics I/O Evolving in 2 Different Directions
- DID (April 26/05) – New APG-79 AESA Radars for Super Hornets. On an interesting note, India had recently shown interest in the Super Hornet and its AESA radar. These latest revelations are likely to fan that interest sharply, and may change the calculus of India’s upcoming fighter purchase if they are approved to receive the radars.
- Australian Aviation (June 2002) – Active Electronically Steered Arrays: A Maturing Technology
