New bottles for old wine

Nov. 1, 1997
WASHINGTON - While U.S. Army leaders are looking for new battlefield surveillance radars to locate hostile artillery and to pinpoint stationary as well as moving targets on the ground, the supporting electronics will be anything but new.

by John Rhea

WASHINGTON - While U.S. Army leaders are looking for new battlefield surveillance radars to locate hostile artillery and to pinpoint stationary as well as moving targets on the ground, the supporting electronics will be anything but new.

Officials are proposing two venerable technologies - bistatic radar and electronically scanned arrays - for these applications in what amounts to repackaging electronics with proven track records to meet stringent requirements evolved from the Army`s experience in the Persian Gulf War.

In the case of the artillery finder, designers from the Amecom Division of Litton Industries in College Park, Md., chose the bistatic approach to separate easily detectable transmitters from the receivers.

The advantages of this approach are significant: operators can maneuver the transmitters to escape enemy detection while the passive receivers remain hidden and operational.

Experts at the Baltimore-based Electronic Sensors & Systems Division of Northrop Grumman Corp., meanwhile, are proposing a derivative of their electronically scanned array on the AH-64D Apache Longbow attack helicopter for such new platforms as the U.S. Army Tracer Future Scout Cavalry System vehicle as well as low-flying surveillance helicopters and fixed-wing aircraft.

There is more than meets the eye to what is common between the Litton and Grumman proposals. Not only do they use mature radar technologies, but they also use commercial off-the-shelf (COTS) electronics that enable designers to shrink the size of the radars to fit on helicopter-deliverable High Mobility Multipurpose Wheeled Vehicles rather than on 5-ton trucks, which greatly improves range and mobility.

Experts from the two companies presented their remarkably similar technical approaches at last month`s Association of the U.S. Army conference in Washington, and they both have their sights set on substantial new programs - and against substantial competition. These programs are likely to be worth as much as $500 million, which will draw interest from other major radar houses such as Hughes Aircraft and Lockheed Martin.

William Foster, vice president for land combat systems at the Northrop Grumman division, summed up the present procurement climate this way: "It`s more about manufacturability and cost control than it is about amazing new physics." In short, what this means is repackaging old technologies to fit in new weapons platforms.

Bistatic radar actually predates today`s self-contained radar systems but it came of age when electronic countermeasures were unknown, and was elbowed aside by the need to put complete radar systems together in ships and aircraft.

Bistatic radar actually was born in January 1931 when the Naval Research Laboratory (then known as the Navy`s Aircraft Radio Laboratory) in Washington set up a project for the "detection of enemy vessels and aircraft by radio." Radar is short for "radio detection and ranging."

The vacuum-tube electronic devices of that time were so primitive that engineers had to separate the receiver and transmitter. This ruled out shipboard use, so Navy leaders passed the project over to the Army the following year. Subsequent collaboration with the British enabled the Royal Air Force to use ground-based radar to detect and defeat attacking German aircraft during the Battle of Britain in 1940.

Now, in a battlefield dominated by electronic countermeasures and other sophisticated threats such as cruise missiles and unmanned aerial vehicles, survivability becomes a critical issue. During the Persian Gulf War the AN/TPQ-37 and the mobile AN/TPQ-36 radars - both 20-year-old systems - could only transmit for a few minutes each hour before moving quickly to elude hostile fire.

By dispersing several radiating transmitters around the passive receiver, operators can turn the transmitters on and off to confuse the enemy and locate the receiver at the tactical operations center. Using the track-while-scan mode, operators can detect as many as 1,500 artillery locations and coordinate attacks in real time on 300 to 500 of them, says Frank Fleischer, vice president for ground systems at Litton.

Another mature technology in Litton`s proposed MARS (multi-aperture radar system) Firefinder is about 20 traveling wave tubes that can degrade gracefully without knocking out the entire system. Even then, Fleischer says the bistatic system will have twice the 25-kilometer range of the TPQ-37 - and four times the range of the mobile TPQ-36 - against artillery.

However, the main concern in the Gulf War was Iraq`s Scud missiles. Litton officials are not publicly pushing their MARS system as a counter to cruise missiles, but Fleischer estimates MARS should be able to detect these threats at ranges of at least 125 miles.

The revival of interest in bistatic radar began in the early 1980s at the U.S. Air Force Rome Laboratory in Rome, N.Y. There, experts considered it for air traffic control applications. Engineers from one of the groups that spun off from the lab, Syracuse Research Corp. in North Syracuse, N.Y., picked up the idea and demonstrated it for the Army`s Communications and Electronics Command (CECOM) under a $12 million advanced technology development effort concluded through prototype testing earlier this year. CECOM officials have since prepared a final request for proposals, which is due out this month with a contract award scheduled for March.

COTS is also a major factor in Northrop Grumman`s proposal, known as Electronically Scanned Array (ESA) XXI to put a lightweight Ka-band all-weather radar on Army ground vehicles. Company executives are relying on their experience on the AN/APN-241 military weather radar, which is also available to commercial users and costs about $30,000. About 200 of these systems have been delivered.

The major change is upgrading the central processor from an Intel 486 to a Pentium, plus the addition of a 28-pound antenna (35 pounds in the helicopter) and a new application-specific gimbal mount. Northrop Grumman officials expect to use software and algorithms from Apache Longbow. The design-to-cost goal has been set at $150,000.

This is also a track-while-scan radar capable of detecting moving targets to up 12 miles and classifying them up to six miles, while detecting and classifying stationary targets up to nearly two miles. The heart of the system is a solid-state array, which moves the antenna electronically rather than mechanically. This essentially is the way the huge ground-based phased array antennas detect strategic missiles.

Survivability is also a concern, and the ESA XXI uses a narrow main beam with low sidelobes and frequency hopping to minimize risk of detection by tactical radar warning receivers. These also are mature technologies.

The two proposed radars illustrate another truth about today`s military electronics climate. These are both computing-intensive applications that would be impossible without the digital signal processing power of today`s microprocessors.

Nobody had even imagined the transistor, let alone the microprocessor, when Navy designers set out to detect hostile aircraft with the miracle technology of that day, radio. Now the microprocessor is the miracle technology, and the opportunities are as limitless as they were in 1931.

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