Plasma Antenna

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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 propagated 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. This is a fundamental change from traditional antenna design that generally employs solid metal wires as the conducting element. Ionized gas is an efficient conducting element with a number of important advantages. Since the gas is ionized only for the time of transmission or reception, “ringing" and associated effects of solid wire antenna design are eliminated. The design allows for extremely short pulses, important to many forms of digital communication and radars. The design further provides the opportunity to construct an antenna that can be compact and dynamically reconfigured for frequency, direction, bandwidth, gain and beam width. Plasma antenna technology will enable antennas to be designed that are efficient, low in weight and smaller in size than traditional solid wire antennas.

When gas is electrically charged, or ionized to a plasma state it becomes conductive, allowing radio frequency (RF) signals to be transmitted or received. We employ ionized gas enclosed in a tube as the conducting element of an antenna. When the gas is not ionized, the antenna element ceases to exist. This is a fundamental change from traditional antenna design that generally employs solid metal wires as the conducting element. We believe our plasma antenna offers numerous advantages including stealth for military applications and higher digital performance in commercial applications. We also believe our technology can compete in many metal antenna applications. Our initial efforts have focused on military markets. General Dynamics' Electric Boat Corporation sponsored over $160,000 of development in 2000 accounting for substantially all of our
revenues.

Initial studies have concluded that a plasma antenna's performance is equal to a
Copper wire antenna in every respect. Plasma antennas can be used for any transmission and/or modulation technique: continuous wave (CW), phase modulation, impulse, AM, FM, chirp, spread spectrum or other digital techniques. And the plasma antenna can be used over a large frequency range up to 20GHz and employ a wide variety of gases (for example neon, argon, helium, krypton, mercury vapor and zenon). The same is true as to its value as a receive antenna.

Market applications of plasma technology

Plasma antennas offer distinct advantages and can compete with most metal
antenna applications. The plasma antenna's advantages over conventional metal elements are most obvious in military applications where stealth and electronic warfare are primary concerns. Other important military factors are weight, size and the ability to reconfigure. Potential military applications include:

  • Shipboard/submarine antenna replacements.
  • Unmanned air vehicle sensor antennas.
  • IFF ("identification friend or foe") land-based vehicle antennas.
  • Stealth aircraft antenna replacements.
  • Broad band jamming equipment including for spread-spectrum emitters.
  • ECM (electronic counter-measure) antennas.
  • Phased array element replacements.
  •  EMI/ECI mitigation
  • Detection and tracking of ballistic missiles
  • Side and backlobe reduction
Military antenna installations can be quite sophisticated and just the antenna portion of a communications or radar installation on a ship or submarine can cost in the millions of dollars.

Plasma antenna technology has commercial applications in telemetry, broad-band communications, ground penetrating radar, navigation, weather radar, wind shear detection and collision avoidance, high-speed data (for example Internet) communication spread spectrum communication, and cellular radiation protection.

Unique characteristics of plasma technology

 

One fundamental distinguishing feature of a plasma antenna is that the gas
ionizing process can manipulate resistance. When deionized, the gas has infinite
resistance and does not interact with RF radiation. When deionized the gas antenna will not backscatter radar waves (providing stealth) and will not absorb high-power microwave radiation (reducing the effect of electronic warfare countermeasures).

A second fundamental distinguishing feature is that after sending a pulse the
plasma antenna can be deionized, eliminating the ringing associated with traditional metal elements. Ringing and the associated noise of a metal antenna can severely limit capabilities in high frequency short pulse transmissions. In these applications, metal antennas are often accompanied by sophisticated computer signal processing. By reducing ringing and noise, we believe our plasma antenna provides increased accuracy and reduces computer signal processing requirements. These advantages are important in cutting edge applications for impulse radar and high-speed digital communications.

Based on the results of development to date, plasma antenna technology has the following additional attributes:

  • No antenna ringing provides an improved signal to noise ratio and reduces multipath signal distortion.
  • Reduced radar cross section provides stealth due to the non-      metallic elements.
  • Changes in the ion density can result in instantaneous changes in bandwidth over wide dynamic ranges.
  • After the gas is ionized, the plasma antenna has virtually no noise floor.
  • While in operation, a plasma antenna with a low ionization level can be decoupled from an adjacent high-frequency transmitter.
  • A circular scan can be performed electronically with no moving parts at a higher speed than traditional mechanical antenna structures.
  • It has been mathematically illustrated that by selecting the gases and changing ion density that the electrical aperture (or apparent footprint) of a plasma antenna can be made to perform on par with a metal counterpart having a larger physical size.
  • Our plasma antenna can transmit and receive from the same aperture provided the frequencies are widely separated.
  • Plasma resonance, impedance and electron charge density are all dynamically reconfigurable. Ionized gas antenna elements can be constructed and configured into an array that is dynamically reconfigurable for frequency, beamwidth, power,gain, polarization and directionality - on the fly.
  • A single dynamic antenna structure can use time multiplexing so that many RF subsystems can share one antenna resource reducing the number and size of antenna structures.

Advantages

The advantage of a plasma antenna is that it can appear and disappear in a few
millionths of a second. This means that when the antenna is not required, it can be made to disappear, leaving behind the gas – filled column that has little effect on the electromagnetic fields in the proximity of the tube. The same will be true for fiber glass and plastic tubes, which are also under consideration.

The other advantage of plasma antenna is that even when they are ionized and in use at the lower end of the radio spectrum, say HF communications, they are still near transparent to fields at microwave frequencies.

The same effect is observed with the use of ionosphere, which is plasma. Every
night amateur radio operators bounce their signals off the ionosphere to achieve long distance communications, whilst microwave satellite communication signals pass through the ionosphere.

  1. Reduced RCS
  2. Reduced interference and ringing
  3. Can change shape to control pattern and bandwidth
  4. Can change plasma parameters
  5. Glow discharge increased
  6. visible signature *
  7. Good RF coupling for electrically small antennas
  8. Frequency selectivity
  9. Stable and repeatable
  10. Efficient
  11. Flexibility in length and direction of path

 


Conclusion

As part of a “blue skies” research program, DSTO has teamed up with the ANU’s
Plasma Research Laboratory to investigate the possibility of using plasmas like those generated in fluorescent ceiling lights, for antennas

The research may one day have far reaching applications from robust military
antennas through to greatly improved external television aerials. Antennas constructed of metal can be big and bulky, and are normally fixed in place. The fact that metal structures cannot be easily moved when not in use limits some aspects of antenna array design. It can also pose problems when there is a requirement to locate many antennas in a confined area.

Weapons System Division has been studying the concept of using plasma
columns for antennas, and has begun working in collaboration with ANU plasma
physicists Professor Jeffrey Harris and Dr. Gerard Borg. Work by the team has already led to a provisional patent and has generated much scientific interest as it is so novel. It offers a paradigm shift in the way we look at antennas and is already providing the opportunity to create many new and original antenna designs

Plasma is an ionized gas and can be formed by subjecting a gas to strong electric or magnetic fields. The yellow lights in streets are a good example of plasmas though a better example is the fluorescent tubes commonly used for lighting in homes.

The type of plasma antenna under investigation is constructed using a hollow
glass column which is filled with an inert gas. This can be ionized by the application of a strong RF field at the base of the column. Once energized, the plasma column can be made to exhibit many of the same characteristics of a metal whip antenna of the type mounted on most cars. The metal whips that may be considered for a plasma replacement are anywhere from a few centimetres to several metres long.
There are many potential advantages of plasma antennas, and DSTO and ANU
are now investigating the commercialization of the technology. Plasma antenna
technology offers the possibility of building completely novel antenna arrays, as well as radiation pattern control and lobe steering mechanisms that have not been possible before. To date, the research has produced many novel antennas using standard fluorescent tubes and these have been characterized and compare favourably with their metal equivalents. For example, a 160 MHz communications link was demonstrated using plasma antennas for both base and mobile stations. Current research is working towards a robust plasma antenna for field demonstration to Defence Force personnel.



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