How subs can radio home from underwater

August 01, 2001

SUBMARINERS in the US Navy will soon be able to surf the Web from deep under the ocean. Their secret? A clever floating antenna that can transmit and receive radio signals, even when waves wash over it.

Submarines already use floating cables for radio communication but they work at very low frequencies, sending voice and data signals at rates far slower than a domestic dial-up modem. To transmit lots of information, subs have to surface to contact satellites, ships, aircraft or ground forces-and so risk detection by an enemy.

What you really need is a way to allow the floating antenna to transmit the ultra-high frequency waves that usually carry high-speed voice, video and Internet signals. But these waves have short wavelengths and are easily absorbed by water. "When waves break over the antenna, you are out of business," said William Stachnik of the Office of Naval Research in Arlington, Virginia.

So the ONR has developed an antenna that solves this problem. Instead of just one long unit, the new design is like a string of sausages: it links up to 12 ultra-high frequency antenna elements. Each added element makes the signal steadier, which reduces noise. Because the elements are never all submerged by waves at the same time, the signal can still get through.

Reconstructing signals from an array of small antennae poses a problem, however. Because each element is bobbing up and down, the signals reach their destination at slightly different times, and combining them isn't easy. So Gary Somers and a team of software engineers at the MIT Lincoln Laboratory in Lexington, Massachusetts, have devised a computer program that does the job, while accommodating the antennae's bobbing motion. But exactly how it does this is classified.

US Navy researchers also refused to comment on how deep a submarine could plunge while towing the new antenna. But tests on prototypes have been successful, says Stachnik. He anticipates that all US subs will be equipped with these antennae in future.
Author: Catherine Zandonella, San Francisco

New Scientist issue: 4TH August 2001


New Scientist

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