A new type of radio antenna resists jamming, requires little electricity, and can squeeze into compact arrays serving many frequencies, physicists report. To manage all that, the device uses a tube of ionized gas, instead of metals such as steel and chromium, to absorb and broadcast radio waves. Such antennae could be ideal for military applications and use in cellular-telephone networks, the researchers say.
A metal antenna broadcasts radio waves when electrical currents slosh back and forth inside the metal. For military and other uses, the century-old technology has three weaknesses: First, to work at low frequencies, metal antennae must be big and therefore easy to see. Second, antennae that operate at higher frequencies are smaller and harder to see, but they reveal their positions by the very signals they send. Third, metal antennae are susceptible to interference or jamming.
Plasma antennae neatly overcome these problems, physicist Igor Alexeff of the University of Tennessee, Knoxville, reported this week at the American Physical Society's annual meeting of its Division of Plasma Physics in Orlando, Florida. The antennae work just like their metal counterparts, except that currents flow through ionized gas, explains Theodore Anderson, Alexeff's collaborator and a physicist at the University of Tennessee, who conceived of the concept in the mid-1990s as a way to allow submarines to communicate more easily while submerged. Because the antennae, which resemble fluorescent lighting tubes, can steer radio beams, they can function just like phased metal arrays but in much smaller packages.
The devices respond to signals only at or below their operating frequency, so the high-frequency signals typically used for jamming simply pass through with no effect, Anderson says. The antennae also can be nested inside one another to serve many radio frequencies simultaneously without interference. And they can operate on a pulsed electrical current without losing signal clarity, which can reduce power requirements 1000-fold, says Anderson, whose Haleakala R&D Inc. in Brookfield, Massachusetts, is attempting to commercialize the technology.
The plasma antennae do not reflect radar signals when they are turned off, making them "stealthy" in terms of military applications. And the lower their operating frequencies, the less detectable they are to radar, which is not the case for low-frequency metal antennae, Anderson says.
It's a promising technology that "could prove to be on the verge of maturity," says electrical engineer Ronald Marhefka of Ohio State University, Columbus. Still, there could be tradeoffs with conventional antennae, he says. For instance, plasma antennae require more power than metal antennae, he says. So they may not revolutionize the technology for all applications, Marhefka says, but they may find important niches.
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