COTS invades radar signal
Commercial off-the-shelf DSPs are in the driver`s seat for future radar systems to enhance performance and stiffen countermeasure immunity
By John Rhea
New generations of digital signal processors (DSPs) and general- purpose microprocessors, which are readily available from commercial sources, are enhancing the power of radar systems - and reducing their vulnerability to jamming and other countermeasures.
The underlying rationale is the growing computational intensity not only of radar operation itself, but also of the measures systems designers take to reduce the vulnerability of radar to hostile jamming, spoofing, and other countermeasures. Designers of military and civilian radar systems are turning to commercial off-the-shelf (COTS) solutions in DSPs, and they like what they see.
"COTS-based processors are just going gangbusters now," exults John Hahn, manager of airborne surveillance at the Northrop Grumman Corp. Electronic Sensors and Systems Division in Baltimore. He cites the Super Harvard Architecture Computer (SHARC) DSPs from Analog Devices Inc. of Norwood, Mass., and the PowerPC microprocessor from Motorola Inc. in Phoenix as the building blocks for the emerging technology of space-time adaptive processing - better known as STAP.
While the PowerPC 604e is finding its way into a wide variety of military and aerospace designs as a general-purpose processor, designers are finding that the PowerPC 604e often can be an especially useful DSP.
"Six or seven years ago signal processing was the big-risk item in cost and development schedules. All had to be in firmware and had to fit in the embedded space," explains Gerry Clancy, vice president of sales and marketing at Bittware Research Systems in Concord, N.H. Now, as a measure of the progress in DSPs, Clancy says he is expecting "gigaflop levels on a chip." Bittware, whose engineers are major users of the Analog Devices SHARC chips, is benefiting from what Clancy calls "families of DSPs."
The key to designing with the new DSPs is defining a system architecture that makes the most of digital signal processing, says Hahn at Northrop Grumman. Efficiencies in "real world" mixes of radar processing problems have risen from the 12-to-15 percent DSP efficiencies of the past to 50 percent now, a rate which adaptive algorithms require, Hahn says. This scales linearly, he says, to comparable reductions of size, weight, power, and cooling requirements for complete systems.
Advantages of STAP
STAP is the simplest countermeasure for radars against jamming, says Thomas Einstein, consulting systems engineer at Mercury Computer Systems in Chelmsford, Mass. The basic problem that STAP addresses is the trouble that most moving target indicator (MTI) radar systems have in detecting small targets in the presence of clutter and jamming. STAP, however, provides the processing muscle that radars need to adaptively emphasize the desired signal and block out extraneous signals and noise.
STAP provides sidelobe steering, which places the null - or the least-sensitive portion of the radar antenna - in the direction of any jamming, Einstein explains. This happens in three steps. First, the system needs an antenna with adjustable sidelobes. Designers cannot do this mechanically, so the radar needs an active-array antenna with a receiver behind each element, including an analog-to-digital (A/D) converter. This requires a lot of signal processing power. Second, the radar has to determine the direction of the jamming signals, which also is a computationally intensive task. Finally, the radar has to generate antenna patterns in which the null is in the direction of the jammer.
Northrop Grumman and Mercury designers are teaming to develop an experimental STAP system for tests by the MIT Lincoln Laboratories in Cambridge, Mass., under the Mountain Top program of the U.S. Navy and Defense Advanced Research Projects Agency (DARPA). The prototype system, built on a VME architecture with Mercury`s Raceway high-speed interconnects, consists of 948 Analog Devices SHARC DSPs and 24 PowerPC RISC processors from Motorola, and has a peak performance of 118 billion floating point operations per second.
Northrop Grumman designers have built experimental radar systems for test flights aboard the company`s own BAC-111 aircraft, Hahn says. Company officials are looking for future applications of this cutting-edge hardware.
One new project, which Hahn says will begin before the end of this year, is to demonstrate a new bistatic radar, which places the radar transmitter and receiver in separate locations. Proposed tests will involve the U.S. Air Force E-3 Airborne Warning and Control System (AWACS) aircraft as the transmitter and the company`s BAC-111 as the receiver.
The basic idea behind bistatic radar is to reduce the radar`s vulnerability. Hostile forces can detect only the emitting transmitter; the receiver is completely passive.
In the planned tests, sponsored by the Air Force Research Laboratory Information Directorate in Rome, N.Y., the AWACS antennas will illuminate the targets, the BAC-111 will receive the data, and then data link the data back to the AWACS. The flight tests will be from an airstrip near the Northrop Grumman Baltimore facility and involve operations over a mixture of mountainous and coastal terrain in the surrounding area.
For the purpose of these tests, the BAC-111 will simulate an unmanned aerial vehicles (UAV). The Air Force`s long-term goal is a fleet of such UAVs as bistatic radar receivers, probably the high-altitude endurance Global Hawk, to get more use out of the AWACS. Even further in the future - by about the year 2025 by some estimates - Air Force officials would like the equivalent of an "AWACS in space," but Hahn estimates this will take considerable improvements in signal processing power, reductions in weight and electrical power requirements, new radiation-hardened components, and new system architectures that will support long-term unattended operation.
Bistatic radar
Barry Isenstein, vice president of Mercury`s Advanced Technology Group, says he sees potential UAV applications for the company`s ruggedized COTS products, particularly synthetic aperture radar processors using SHARC and PowerPC chips packaged on VME printed circuit boards. Radar and sonar require heavy loads of interconnections, and Mercury is offering what Isenstein calls a "Leggo set" of some two dozen board types that can support anywhere from four to 4,000 processors with the same software.
Despite bistatic radar`s potential for reduced vulnerability, leaders of the U.S. Army Communications-Electronics Command (CECOM) at Fort Monmouth, N.J ., turned down this technology for upgrades to their AN/TPQ-37 Firefinder artillery-locating radar, which saw use in the Persian Gulf War. In May CECOM officials selected Raytheon Systems Co. (formerly Hughes Radar Systems) in El Segundo, Calif., for engineering manufacturing development of the program on the strength of the company`s proposal to use solid-state transmitters instead of the conventional traveling wave tubes (TWTs).
The solid-state approach will enable Army officials to mount the improved Firefinder transceivers on 2-1/2-ton trucks rather than on the 5-ton trucks used in the past. The new radar, to be renamed the TPQ-47, should increase mobility, but will not reduce vulnerability to enemy detection. The radar will have a range of about 31 to 37 miles and must be turned on for 30 to 60 seconds at a time and then moved, like the original TPQ-37. Raytheon`s contract is worth $73.7 million, of which CECOM initially committed $800,000 for the first three prototypes.
Leaders of the losing bidder in the competition, Litton Amecom Division in College Park, Md., had proposed a bistatic multi-aperture radar system using 20 TWTs per transmitter. The transmitters would have been scattered around the battlefield and turned on and off intermittently while the passive receivers were located near the tactical operations centers (TOCs). The TOCs could operate continuously but would escape detection because they would not radiate tell-tale signals.
Litton officials are still interested in the bistatic approach, says Richard Aronson, a staff scientist at Amecom. They are considering using it in a track-while-scan mode for the Army`s next major ground-based radar competition, an upgrade to the TPQ-36 mortar-finding radar. The TPQ-36, also used in the Gulf War, operates at X-band with a range of nine to 12 miles. The CECOM-sponsored EMD phase is expected in about two years. Also, to increase mobility, Army leaders say they would like to install the radar in helicopter-deliverable High Mobility Multipurpose Wheeled Vehicles - better known as humvees.
Low-temp, co-fired ceramic
Another technology under consideration for radar applications (and also for commercial cellular phone, pager, and cordless telephone applications) is in the works at National Semiconductor Corp. in Santa Clara, Calif. This technology is called low-temperature co-fired ceramic (LTCC), which provides high functional density by integrating passive components on one substrate as thick as 50 layers.
LTCC increases processing speed, which can reduce the time an enemy has to lock on to a transmitter, explains Jim Martin, a consultant to National. Increased processing density also improves target resolution and rejects spurious signals.
National experts participated in a DARPA-sponsored project in 1996 in which they used LTCC devices in a receiver in the AIM-120 Advanced Medium Range Air-to-Air Missile (AMRAAM). The technology is one-forth the size of conventional devices. Air Force officials did not pay for production, however, after it tested two prototypes. Nonetheless, Larry Dano, an applications engineer at National`s military and aerospace operations, says any packaging technology that offers a radical increase in functional density is a logical candidate for the advanced systems of the future. Among the potential applications are hand-held radios and global positioning system receivers.
Despite the momentum of general-purpose DSPs, leaders of Sharp Microelectronics Technology in Camas, Wash., are finding a niche in the high-end market for DSPs optimized for Fast Fourier Transform (FFT) and other block computing. Radar has historically been analog, explains Rod Hofer, applications engineer at Sharp. High-end DSPs, he says, are taking over increasing numbers of analog radar functions, and are improving system performance as they do so.
There is, of course, a tradeoff between the widely sold and relatively inexpensive general-purpose DSPs and the more costly devices that are optimized for complex tasks, but Steven Sidman, a fellow at Sharp, notes that growing acceptance should drive down costs. In addition to radar, applications include sonar, medical imaging, and high-end communications.
Sharp`s 9124 can process a 1,000-point complex FFT in 65 microseconds at 50 MHz. The "one off" price is about $1,000, Sidman says. Users can configure the same devices to handle 4,000 and 8,000 FFTs, and in the future as many as 32,000 FFTs as radars require even more computing power. They are particularly attractive, he adds, for hetero-geneous computing. Sharp engineers design their own DSP line, and fabricate them in Japan at parent Sharp Corp. of Osaka.
Low-end DSP processing
At the other end of the spectrum, low-end Doppler weather radar applications, engineers at Bittware Research are using SHARC DSPs that cost as little as $10 apiece in quantity. The availability of such inexpensive devices is opening up markets for DSPs in speech recognition and professional audio applications, thus creating even greater economies of scale - and price breaks for radar systems integrators.
Bittware engineers are delivering a half-length PC board with a single SHARC DSP for a Doppler radar that pinpoints storms and creates high-resolution displays for television meteorologists. This system, from Radtec Engineering in Broomfield, Colo., processes the radar signals in real time. The DSP has a 32-bit floating-point core that performs 120 million floating point operations per second and typically runs at 40 MHz. These devices cost around $200 each, but the prices are declining.
Radar receivers of this type typically use separate modules: a low-noise amplifier, mixer, and post-amplifier. Yet by using Bittware Research`s Blacktip DSP board, Radtec experts integrated a low-noise unit with the ability to detect weak signals such as light rain or snowfall, and overwhelming signals such as severe thunderstorms, all simultaneously.
The net result of the current revolution in digital signal processing: devices are now available across the entire price spectrum and COTS solutions are accessible for a comparably broad range of radar applications.
The Joint Surveillance Target Attack Radar System`s radar antenna from the Northrop Grumman Norden Systems unit, pictured above, helps U.S. military leaders detect, locate, classify, track, and target hostile ground movements.
COTS DSPs such as the Sharp Microelectronics Butterfly, pictured above in packaging from Chip Supply, are finding a niche in the high-end market for DSPs optimized for Fast Fourier Transform and other block computing.
Radar is a phone call away
CHARLOTTESVILLE, Va. - Executives of Litton Marine Systems are distributing shipboard radar systems and spares worldwide as commodity items under a new program launched in June known as Ready Radar.
Under the Ready Radar program, officials of Litton Marine of Charlottesville, Va., stock equipment in bonded stores at company depots, where they are available for order via an automated telephone ordering system, says Nolasco DaCunha, Litton`s vice president for sales and service.
Litton technicians then install the equipment when the ship reaches its next port. The company has 300 depots in North America, Europe, the Far East and the Middle East, DaCunha adds.
Managing the Ready Radar program is Decca Marine Ltd. of New Malden, England, one of three Litton business units involved in the program. The others are Sperry Marine and C. Plath in Hamburg, Germany.
For more information on the Ready Radar program, contact Sperry Marine by phone at 804-974-2000, by fax at 804-974-2259, by post at 1070 Seminole Trail, Charlottesville, Va. 22901 or on the World Wide Web at http://www. sperry-marine.com/. - J.R.
Real-time radar simulation tool kit
ALBUQUERQUE, N.M. - A radar scene simulation package originally used at the Federal Aviation Agency (FAA) to model radars to determine clutter in the environment has several military and aerospace applications.
Managers of several military programs, including the Joint Strike Fighter (JSF) and unmanned aerial vehicles (UAVs) employing synthetic aperture radar (SAR) are looking into this simulation package called RadarWorks from Photon Research.
This tool was introduced in January, and SAR and Doppler beam shaping capabilities were added in July, according to Chris Blasband, staff scientist at Photon Research Associates Inc. in San Diego. The purpose is to develop pixelized radar cross section (RCS) maps in real-time in order to generate radar displays correlated with the visible out-the-window view.
This is a commercial off-the-shelf (COTS) product for applications spanning cockpit design, radar system performance, human factors, and mission rehearsal and planning, Blasband says.
The FAA has bought three packages, and two others have been delivered to military prime contractors that he could not name. RadarWorks is a module in the Vega software package of Paradigm Simulation Inc., Dallas, which acts as Photon Research`s value-added reseller.
For more information on RadarWorks, contact Paradigm Simulation by phone at 972-960-2301, by fax at 972-960-2303, by post at 14900 Landmark Blvd., Suite 400, Dallas, Texas 75240, or on the World Wide Web at http://www. paradigmsim.com/. - J.R.
COTS DSP software packages emerge
NATICK, Mass. - Radar systems designers often start with a robust set of tools for programming ever-more-powerful digital signal processors (DSPs). But then they face the task of tailoring the software to their real-time programmable chips.
Yet in doing this they do not have to reinvent the wheel, say officials of The MathWorks Inc. in Natick, Mass. All these designers face the same problem; getting the DSP out the door and doing the preliminary algorithm exploration and validation that is required, company officials say.
Yet Mathworks experts have developed an all-purpose integrated tool suite called the MathWorks DSP Workshop, an integrated open environment for algorithm exploration, development, simulation, and implementation.
The alternative is the one-at-a-time approach of writing new code for each new chip architecture, but then the designers have to do it all over again for the next project, company officials say. This consumes time and money, both in short supply.
The DSP Workshop, which is capturing the interest of designers sonar systems, costs about $4,300. It consists of four products: the Matlab collection of array math and signal processing functions, Simulink block diagram interface, Signal Processing Toolbox, and DSP Blockset. The package runs on all the standard personal computers and workstations using Windows 95 or NT operating systems.
For more information on the DSP Workshop or related products, contact The MathWorks by phone at 508-647-7000, by fax at 508-647-7001, by post at 24 Prime Park Way, Natick, Mass. 01760, or on the World Wide Web at http://www. mathworks.com/. - J.R.
PowerPCs from Sky run foliage penetrating SAR
CHELMSFORD, Mass. - Officials of Sky Computers Inc. in Chelmsford, Mass., are supplying their 6U VME Excalibur boards (recently upgraded to the Motorola PowerPC 604e) as the heart of a new VHF/UHF synthetic aperture radar (SAR) for foliage penetration being developed by Lockheed Martin Tactical Defense Systems in Goodyear, Ariz.
The program is sponsored by the Defense Advanced Research Projects Agency in Arlington, Va., the U.S. Army Communications-Electronics Command at Fort Monmouth, N.J., and the U.S. Air Force Research Laboratory in Rome, N.Y.
The program aims at finding targets such as tanks, armored personnel carriers, and mobile missile launchers in foliage at near real-time rates. Future plans call for mounting the SAR and a real-time signal processor in an unmanned aerial vehicle to search forests.
This is a particularly demanding application, notes Richard Jaenicke, director of marketing at Sky, because of the constrained space and budget combined with the need for high data rates. The multiprocessor Skychannel 64-gigaflop system communicates over the VME P2 backplane connector.
Sky designers are using the same technology in a mobile 3D radar system for the Telecommunications Research Institute in Warsaw, Poland. The ruggedized VME 6U system, which also costs less than $1 million, uses 32 Excaliburs and seven SHARC-based SHARCpool motherboards.
The purpose is for air surveillance against low-flying aircraft and cruise missiles, and the mobile radar has eight separate receiving antenna beams with low-level sidelobes, adaptive moving target indicator systems, pulse compression, and post-detection filtration of tracks.
Company officials decided up front to take a commercial off-the-shelf approach, Jaenicke notes, but even this level of technology would have been impossible to export to a former Soviet bloc country until a few years ago. Yet the same basic technology is being employed in advanced U.S. military programs and a relatively less advanced 58-gigaflop ground-based system in Poland.
For more information on the Excalibur single-board DSP, contact Sky Computers by phone at 978-250-1920, by fax at 978-250-0036, by mail at 27 Industrial Ave., Chelmsford, Mass. 01824, or on the World Wide Web at http://www.sky.com/.- J.R.
