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Plasma Antennas


Published on Dec 12, 2015

Abstract

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.

he 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.

Plasma Generation and Containment

For antenna applications the plasma must be maintained in precise spatial distributions, such as filaments, columns, or sheets. The plasma volume can be contained in an enclosure (tube) or suspended in free space. Compositions that may be used to form plasma in a tube include gases of neon, xenon, argon, krypton, hydrogen, helium, and mercury vapor. Energizing the plasma can be accomplished with electrodes, fiber optics, microwave signals, lasers, RF heating, or electromagnetic couplers. The tube confines the gas and prevents diffusion. The radiation pattern is controlled by parameters such as plasma density, tube shape, and current distribution.

A conventional tube has the disadvantage of requiring two or more contacts (electrodes) for applying the ionizing potential. As an alternative, a surface wave can be used to excite the plasma from a single end.

The surface space-charge wave 2 is electro-mechanical in nature. A time-harmonic axial electric field is applied a one end of the plasma column. Charges are displaced and restoring electric fields are set up in response to the applied field. The charges remain balanced in the interior of the plasma, but the electric field causes a deformation of the plasma surface that results in a surface charge layer.

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 beamwidth. 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 nd 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-spectum 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.














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