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Definition
Plasma antennas are radio frequency antennas that employ plasma as the guiding
medium for electromagnetic radiation. The concept
is to use plasma discharge tubes as the antenna elements. When the tubes are energized,
they become conductors, and can transmit and receive radio signals. When they
are de-energised, they revert to non-conducting elements and do not reflect probing
radio signals. Plasma antenna can be "Steered" electronically. Another
feature of the plasma antenna is that it can be turned off rapidly, reducing ringing
on pulse transmission.On earth we live upon an island
of "ordinary" matter. The different states of matter generally found
on earth are solid, liquid, and gas. Sir William Crookes, an English physicist
identified a fourth state of matter, now called plasma, in 1879. Plasma is by
far the most common form of matter. Plasma in the stars and in the tenuous space
between them makes up over 99% of the visible universe and perhaps most of that
which is not visible. Important to ASI's technology, plasmas are conductive assemblies
of charged and neutral particles and fields that exhibit collective effects. Plasmas
carry electrical currents and generate magnetic fields.
When
the Plasma Antenna Research Laboratory at ANU investigated the feasibility of
plasma antennas as low radar cross-section radiating elements, Redcentre established
a network between DSTO ANU researchers, CEA Technologies, Cantec Australasia and
Neolite Neon for further development and future commercialization of this technology.
The plasma antenna R & D project has proceeded over the last year at the Australian
National University in response to a DSTO (Defence Science and Technology Organisation)
contract to develop a new antenna solution that minimizes antenna detectability
by radar. Since then, an investigation of the wider technical issues of existing
antenna systems has revealed areas where plasma antennas might be useful. The
project attracts the interest of the industrial groups involved in such diverse
areas as fluorescent lighting, telecommunications and radar. Plasma antennas have
a number of potential advantages for antenna design.
When
a plasma element is not energized, it is difficult to detect by radar. Even when
it is energized, it is transparent to the transmissions above the plasma frequency,
which falls in the microwave region. Plasma elements can be energized and de-energized
in seconds, which prevents signal degradation. When a particular plasma element
is not energized, its radiation does not affect nearby elements. HF CDMA Plasma
antennas will have low probability of intercept( LP) and low probability of detection(
LPD ) in HF communications. Plasma
Antenna Technology
Since the discovery of
radio frequency ("RF") transmission, antenna design has been an integral
part of virtually every communication and radar application. Technology has advanced
to provide unique antenna designs for applications ranging from general broadcast
of radio frequency signals for public use to complex weapon systems. In its most
common form, an antenna represents a conducting metal surface that is sized to
emit radiation at one or more selected frequencies.
Antennas must be efficient
so the maximum amount of signal strength is expended in the propogated wave and
not wasted in antenna reflection.
Plasma antenna technology employs ionized
gas enclosed in a tube (or other enclosure) as the conducting element of an antenna.
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