How subs can radio home from underwater
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
