Far from being an antique curiosity of World War II, radar technology today has become smaller, cheaper, easier to manufacture, and more powerful.

Modern radars can look beneath the Egyptian desert from an orbiting spacecraft and see ancient riverbeds and ruins. From miles away, they can peer through clouds or fog to figure out what a ship at dock looks like by sensing patterns from its rocking motion. They soar overhead in small, unmanned planes to give military commanders a live picture of a battlefield in any weather, day or night.

Yet the most surprising accomplishment of this military-driven technology may be its steady move into civilian life. Already, people barely notice when radar calls a fault at tennis tournaments or delivers a more accurate weather forecast. So hold onto your radar detectors, scientists say.

There's much more to come as military breakthroughs spark creative new ideas for civilian use - from making seven-day forecasts as accurate as today's two-day predictions to building cars that warn lane-changing drivers of a car they can't see.

In the military, radar remains the backbone of America's missile-defense system.

"[Radar] does everything from large-scale surveillance to identifying a specific threatening object and actually guiding the kill-vehicle [missile] to it," says Rick Yuse, vice president of the missile-defense program at Raytheon, a major US defense contractor.

Today's technology is allowing powerful radars to be built that would have been unimaginable to scientists who built giant radar towers in the late 1930s to defend Britain's coastline.

But while giant missile-defense radars, such as the BMEWS systems, may mushroom to 10 or 12 stories tall, much of the most exciting research in radar is thinking small.

Just coming on line for aircraft, for example, is Active Electronically Scanned Array (AESA) radar, a fully electronic radar with no mechanical moving parts that can track many targets and guide missiles to those targets simultaneously. It is operating on just 18 US Air Force F-15s. There are plans to equip 161 more F-15s and other military aircraft in the future.

AESA is "stealthier" and more reliable than older radars and may eventually be put to use helping to intercept cruise missiles. Some evidence suggests it is powerful enough to knock out ground-based radars if its beam is concentrated on a narrow spot. That task, though, is expected to be handled mostly by the military's new Thor radar-jamming system, expected to be available in 2008.

Another radar in the works, the mini-SAR, has gained tremendous attention in recent months. Synthetic aperture radar (SAR), often called "imaging radar" because of its ability to show stationary objects with almost photographic clarity, has been used in reconnaissance aircraft like the U-2 for years. Now scientists at Sandia National Laboratories in Albuquerque, N.M., are miniaturizing it to fit into the tiny unmanned Shadow aerial vehicle, not much bigger than a model airplane.

SAR images are nothing like the smears of light seen on early radar screens. With a miniSAR, weighing less than 30 pounds, the Shadow could distinguish two Coke cans standing only inches apart from several miles away, says George Sloan, the miniSAR project leader at Sandia. And many radar images must be interpreted by an image analyst. Not so with SAR, Mr. Sloan says. That means troops can view images themselves and act quickly.

"I can show these images to my 10-year-old son, and he'll be able to identify a car, a truck, a building, or whatever," Sloan says.

The group hopes to flight test the miniSAR in early 2005.

Eventually, Sloan says, the miniSARs might be small enough, and cheap enough, to be put inside precision-guided bombs, for use when guidance systems such as GPS are not practical or are being jammed.

But no matter how much radar is doing now, military planners want it to do more.

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