The new breed of radar and EW can sense the RF environment and adapt itself in nanoseconds for the best possible performance, which is placing new demands on digital signal processing and digital conversion technology.
Today's electronic battlefield is more complex and deadly than ever-particularly when it comes to electronic surveillance and electronic warfare. Modern radar systems have the ability to reach out and touch the environments in which they operate, detect and characterize sources of electronic noise such as RF jamming or co-location antenna interference, and adapt the radar's performance to compensate.
This kind of technology is called digitally programmable or adaptive radar. The idea is for modern radar digital signal processing (DSP) to sense and compensate for jamming and interference quickly, adapt its transmit/receive modes, and continue with the radar system's primary mission-be it military air traffic control, detecting and characterizing potential targets, or keeping a close watch for approaching threats.
The emerging ability for radar and EW systems to adapt rapidly to their environments is creating an electronic cat-and-mouse game that plays out at ever-increasing speed, as radar systems seek to adapt more quickly than the EW systems that oppose them, and likewise as EW systems seek to jam ever more quickly adaptable radar.
"It's so time-critical to follow signals that are continually adapting," points out Denis Smetana, product marketing manager for field-programmable gate array (FPGA) products at high-performance embedded computing (HPEC) specialist Curtiss-Wright Controls Defense Solutions in Ashburn Va.
Digitally programmable radar
RF and microwave technology that uses agile waveforms for security and anti-jam capability isn't new. The U.S. Single-Channel Ground and Airborne Radio System (SINCGARS), for example, has been using this approach since the 1980s to foil jamming and attempts to eavesdrop on important military voice conversations and data transmissions.
The way it works is the system's transmitter and receiver rapidly hop among a predetermined set of frequencies in a set sequence. The idea is that such a fast-moving target is extremely difficult to jam or intercept. Only those with a key to the frequency dance can participate on that radio network.
Now extend that concept to radar. A frequency-agile radar signal dancing among many different frequencies not only is difficult to detect, but it also is difficult to jam or spoof. An adversary trying to jam it often is faced with jamming a wide swath of the RF spectrum. Not only does this take a lot of power, but it also has the potential to deny the adversary parts of the RF spectrum he's trying to use himself. Sometimes broadband jamming simply isn't worth it.
Now take the notion of a frequency-agile radar one step further to digitally programmable adaptive radar. This type of system takes a more active approach to foiling attempts to spoof or jam it, by using a type of built-in electronic intelligence (ELINT) subsystem. This adaptive radar listens for RF emissions in its vicinity with potential to disrupt it, and automatically adjusts its operations to compensate-whether that involves finding unaffected frequencies or using other methods to defeat jamming and other kinds of RF noise.
This ability to reach out and touch its environment and to move quickly to compensate is not limited only to radar. Tomorrow's military radio communications also may have similar capabilities in future systems known as cognitive radio.
"Cognitive radio is a catchall for many things, like bandwidth exploitation," explains Rodger Hosking, vice president of embedded computing provider Pentek Inc. in Upper Saddle River, N.J. "This is where a system could find the frequencies that are not being used, or are not being jammed on the sending and receiving end, to send a clear signal. A minute later, it might do the same thing to evade the jamming and maintain a reliable radio link."
This cognitive quality in adaptive radar works on the same principle. "If you are talking about radar, you have a similar kind of adaptive capability," Hosking says. Compounding the problem is the growing complexity of radar and radar signal processing. Today's radar technology is being asked not only to detect targets, but also to characterize them as large or small, friendly or hostile, and sometimes even provide radar images of the target.
"We need radar with the sensitivity to detect targets with much smaller radar cross sections than we had in the Cold War, and radars at sea must work in high sea states," says Paul Monticciolo, chief technology officer of digital signal processing expert Mercury Systems in Chelmsford, Mass. Such complexity poses the need for extremely advanced digital technologies on the radar as well as the EW side.
|Modern radar systems can sense their operating environments and adapt quickly to electronic jamming and other kinds of RF interference.|
Put yourself in the shoes of an electronic warfare expert trying to defeat digitally programmable radar. He would need some kind of ability to sense how the radar is adapting, use algorithms that anticipate how the radar is behaving, and then transmit jamming signals fast enough to keep up with the radar's movements. It's a cat-and-mouse game that radar and EW technicians have been playing since radar and EW were invented, yet the rules of the game today are moving more quickly than ever.
"If you are a countermeasure and try to defeat a radar pulse, you could look to see what frequency the enemy radar is using and tune the power of a jamming signal to defeat that frequency," says Pentek's Hosking.
In the future, the complexities of these technologies will continue to increase. "The integrated closed-loop system is where things may be going in the future," says Mercury's Monticciolo. "That is, taking some action based on that signal, and then send out a waveform to defeat the enemy that is trying to do something to me."
The key enabling technologies for the most advanced adaptable radar and EW systems today include extremely fast analog-to-digital (A/D) converters and digital-to-analog (D/A) converters, digital processors, and high-speed digital interconnects.
Among the most crucial technologies are A/D and D/A converters. These are the devices that sit between the transceiver antennas and digital signal processing. Nanoseconds count when it comes to A/D and D/A converters, because no matter how fast the processors are, they can't perform at top levels if they don't get input and output from digital conversion in a timely manner.
One of the fastest available D/A converters, introduced in March, is the TDAC-25 from Tektronix Component Solutions in Beaverton, Ore. The 10-bit D/A converter is packaged as an application-specific integrated circuit (ASIC) and offers performance of 25 gigasamples per second.
Tektronix, a well-known manufacturer of RF test and measurement equipment like spectrum analyzers and oscilloscopes, capitalized on its experience in high-speed test equipment to craft the new device. Company officials say the TDAC-25 aims at next-generation embedded systems in such areas as defense, commercial aerospace, medical, and coherent optical communications. This device is at the heart of the Tektronix AWG70000 arbitrary waveform generator.
The TDAC-25 has dynamic ranges to -80 dBc narrowband and -60 dBc wideband, and in RF- based applications it supports direct-generation of wideband signals, reducing complexity through the elimination of D/A converter arrays and frequency conversion blocks.
The TDAC-25 already has been designed into two next-generation systems under development, including the CHAMP-WB-DRFM 6U Virtex-7 VPX module from Curtiss-Wright Controls Defense Solutions. Of particular interest in defense applications is the device's low-latency where it can deliver the fast response needed for electronic warfare systems, Tektronix officials say.
The Curtiss-Wright CHAMP-WB-DRFM leverages Tektronix digital converter technology developed for the test and measurement world, Curtiss-Wright officials say. The board set incorporates this leading-edge technology in an open standards format that is much easier to integrate into deployable systems.
The board provides two to three times the level of performance for applications that require wideband capability and low latency in defense and aerospace such as DRFM, EW, signal intelligence (SIGINT), and electronic counter measures (ECM), and in commercial applications such as direct RF digitization, ground-penetrating radar (GPR), and coherent optical applications.
"Now, in terms of latency, in sampling a signal you no longer have to pass data from an FPGA to another to get out," says Curtiss-Wright's Smetana. "It allows us to cut tens of nanoseconds for each pass." For adaptive radar and EW, the value of next-generation digital converters like the TDAC-25 cannot be overstated. "These chips are the special sauce," says Eran Strod, systems srchitect at Curtiss-Wright.
|A Navy petty officer works on the Electronic Warfare module aboard a deployed aircraft carrier.|
In terms of digital signal processing for adaptive radar and EW, the field-programmable gate array (FPGA) is king, designers say. The reason is the FPGA's ability to process quickly changing information, but also its ability to be to be reprogrammed on the fly to adapt to changing operating conditions.
"The FPGA concept of partial reconfiguration now can change an algorithm while the FPGA is running," Smetana says. "We need to figure out what do I reconfigure, and when do I reconfigure it."
The fast and predictable performance of FPGAs-as opposed to general-purpose graphics processing units (GPGPUs) or general-purpose processors like the Intel Core i7-is what makes them so attractive to today's radar and EW systems designers.
"FPGAs are the only type of programmable computing device with very low latency and predictable response," says Dan Veenstra, product manager of sensor processing platforms at GE Intelligent Platforms on Ottawa.
Veenstra describes a kind of radar spoofing EW that quickly samples a radar system's characteristics such that the EW system can manipulate return signals to make targets look like some things they're not. "You can actively transmit a reflection of your own design, so instead of one aircraft, you can look like a squadron of aircraft," he says.
The enabling technology challenges of such a capability are major challenges. "We need to have enough dynamic range on the A/D converters, and need to read memory in and out at a very high rate," Veenstra says. "You read in the receive signature, and you need to read out of that memory many repeated versions with the desired characteristics. You need the FPGAs to do the echo modification; the aircraft creates its own radar echo, but you want artificial echoes. You need to get that reflection out of memory and over the air as quickly as possible to make it look realistic. That is the high level of what our customers are trying to implement."
Systems designers also are looking at new generations of smart FPGAs with embedded microprocessors not only to increase performance, but also to shrink electronic components in the interests of saving size, weight, and power (SWAP), Veenstra says.
"The main advances, other than shrinking the die and getting power down, is the addition of embedded processors," Veenstra says. "ARM is the most popular in the FPGAs to make the devices more autonomous. It gives you two functions in slot because you don't need the separate CPU to make the decision of what and when to run in the operating system."
One of the most promising embedded processing technologies from GE Intelligent Platforms for adaptive radar and EW is the SPR870A 3U VPX wideband digital receiver/exciter module, which packs a lot of capability into a small package for applications such as unmanned aerial vehicles (UAVs), Veenstra says.
Pentek engineers are designing company signal processing boards and subsystems to be as flexible and applicable to as wide a range of end products as possible, Hosking says. "Of all our products that use FPGAs and that use digital upconverters, A/Ds, and D/As, the person who is using these boards can program the frequencies with 32 bits of resolution so they are tunable across the range of frequencies they can receive."
"We provide products that work in radar, data acquisition, telemetry, and medical imaging that need different frequencies and different bandwidths," Hosking says. "Our products are highly configurable across the control interface."
Hosking also sings the praises of FPGAs for their configurability in radar and EW applications. "We use a technology called Gate Express that allows the system to reconfigure the FPGA at runtime without rebooting," he says. "A user may need to adapt to a different application; one kind of radar might need one kind of FPGA, and a different radar another."
Despite the obvious advantages of FPGAs in modern radar and EW applications, some processors could benefit from blending FPGAs, GPGPUs, and general-purpose processors, points out Mercury's Monticciolo.
"A designer may use FPGAs as the interface between the A/D converter in the radar, and use that to do some smart beamforming," Hosking says. "He may use GPUs to do some radar signal processing like pulse compression and Doppler filtering. Then he might use Intel processors to track the signal and determine the appropriate waveforms to counter it."
Design and development tools for adaptive radar and EW systems
Designers of modern adaptive radar and electronic warfare systems are learning some of the best ways to blend field-programmable gate arrays (FPGAs), general-purpose graphics processing units (GPGPUs), and general-purpose processors, but much of the most difficult design work involves algorithms.
That's where design and development tools libraries like those from The MathWorks in Natick, Mass., can come into play.
"Algorithms and logic do the tuning and updating of the digital signal processing," says Jon Friedman, aerospace and defense marketing manager at The MathWorks. "Any intelligent system is only as intelligent as what you train it on, so it's critical to have the environment to do that."
One product from The MathWorks is the Phased Array System toolbox, with monostatic and multistatic radar capabilities, including point targets, free-space propagation, clutter models, and barrage jamming.
"Radar is in the RF spectrum, and once you have your algorithms, you need a good model of the RF elements," Friedman says. The company also provides the SimRF simulation product that enables designers to model active and possible RF components like amplifiers, mixers, and transformers. "It gives you the building blocks so you can model the RF components of a system," he says.
DARPA electronic warfare project to counter programmable adaptive radar
Six U.S. research organizations have been chosen to participate in a military electronic warfare (EW) project to find ways to detect and counter digitally programmable radar systems that have unknown behaviors and agile waveform characteristics.
The BAE Systems Electronic Systems segment in Merrimack, N.H., and Systems and Technology Research (STR) in Woburn, Mass., are the latest to join the Adaptive Radar Countermeasures (ARC) program of the U.S. Defense Advanced Research Projects Agency (DARPA) in Arlington, Va.
Last month, BAE Systems won a $36.7 million DARPA contract and STR won a $7.1 million contract to participate in the ARC program. Also last month, DARPA ARC contracts went to Science Applications International Corp. (SAIC) in McLean, Va., worth $31.5 million, and to Vadum Inc. in Raleigh, N.C., worth $4.1 million.
In February, Helios Remote Sensing Systems Inc. in Rome, N.Y., won a $2.9 million DARPA ARC contract, and the Michigan Tech Research Institute (MTRI) in Ann Arbor, Mich., won an $8 million DARPA ARC contract.
The DARPA ARC program seeks to develop EW capability to counter hostile adaptive radar systems based on their over-the-air signals. The program aims to counter enemy radar that senses its environment and automatically adapts to attempts to jam it.
Today's airborne EW systems are proficient at identifying analog radar systems that operate on fixed frequencies. Once they identify a hostile radar system, EW aircraft can apply a preprogrammed countermeasure technique.
The job of identifying modern digitally programmable radar variants using agile waveforms is becoming more difficult. The six ARC contractors will work to enable systems to generate effective countermeasures automatically against new, unknown, or ambiguous radar signals in near real time.
Radar and EW experts at the six companies will develop new processing techniques and algorithms that characterize enemy radar systems, jam them electronically, and assess the effectiveness of the applied countermeasures.
The goal of the DARPA ARC program is to develop ways to counter adaptive radar threats quickly based on over-the-air observable signals.
|Cryptologic technicians monitor electronic emissions in the electronic warfare module aboard the Nimitz-class aircraft carrier USS Ronald Reagan.|
Threats of particular interest include ground-to-air and air-to-air phased array radars capable of performing several different functions, such as surveillance, cued target acquisition, tracking, non-cooperative target identification, and missile tracking. These kinds of radar systems are agile in beam steering, waveform, coding, and pulse repetition interval.
Key challenges to the ARC contractors are how to isolate signals clearly amid hostile, friendly, and neutral signals; figuring out the threat the signal poses; and jamming the signal.
Today's airborne electronic warfare (EW) systems match enemy radar signals and determine appropriate countermeasures based a list of known threats, but are limited when enemy signals are ambiguous or not on the list.
Modern enemy radar systems, however, are becoming digitally programmable with unknown behaviors and agile waveform, so identifying and jamming them is becoming increasingly difficult.
Things will get worse in the future as radars develop the ability to sense their environment and adapt their transmission characteristics and pulse processing algorithms to defeat attempts to jam them.
The objective of the six companies involved in the ARC program is to enable EW systems to generate effective countermeasures automatically against new, unknown, or ambiguous radar signals as they are encountered.
The organizations will try to develop new processing techniques and algorithms to counter adaptive radar threats through real-time analysis of the threat's over-the-air observable properties and behaviors.
The program will develop a closed-loop system with signal analysis and characterization, countermeasure synthesis, and countermeasure effectiveness assessment. The system not only will be able to learn automatically to counter new radar threats, but also will enable human operators to command and receive feedback from the system.
DARPA officials say that software algorithms the ARC contractors develop under the ARC program most likely will be used in existing or planned EW systems.
The ARC program should be able to isolate agile unknown radar threats in dense, complex electromagnetic environments with friendly, hostile and neutral RF emitters; counter these new radar threats; provide real-time feedback on countermeasure effectiveness; counter several threats at once; support single-platform or distributed, multi-platform operations; support autonomous and human-in-the-loop operation; and use a standards-based, modular, open and extensible software architecture. The system also should be able to store and download new knowledge and countermeasures for post-mission analysis.
The ARC program is a five-year effort. The first 30 months focuses on algorithm development and component level testing; the second 18 months focuses on systems development; and the remaining two years is for building a real-time ARC prototype.