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鈥攁nd 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. 鈥淲hen waves break over the antenna, you are out of business,鈥� said
William Stachnik of the Office of Naval Research in Arlington, Virginia.
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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鈥檛 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鈥檚 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.