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DefinitionPlasma antennas are radio frequency antennasthat employ plasma as the guiding medium forelectromagnetic radiation.The concept is to use plasma discharge tubesas the antenna elements. When the tubes areenergized, they become conductors, and cantransmit and receive radio signals. When theyare de-energised, they revert to non-conducting elements and do not reflectprobing radio signals. Plasma antenna can be"Steered" electronically. Another feature of theplasma antenna is that it can be turned off rapidly, reducing ringing on pulsetransmission.On earth we live upon an islandof "ordinary" matter. The different states of matter generally found on earth are solid,liquid, and gas. Sir William Crookes, an Englishphysicist identified a fourth state of matter,now called plasma, in 1879. Plasma is by farthe most common form of matter. Plasma inthe stars and in the tenuous space betweenthem makes up over 99% of the visibleuniverse and perhaps most of that which is notvisible. Im ortant to ASI's technolo lasmas

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When the Plasma Antenna ResearchLaboratory at ANU investigated the feasibilityof plasma antennas as low radar cross-section

radiating elements, Redcentre established anetwork between DSTO ANU researchers, CEATechnologies, Cantec Australasia and NeoliteNeon for further development and futurecommercialization of this technology. Theplasma antenna R & D project has proceededover the last year at the Australian NationalUniversity in response to a DSTO (DefenceScience and Technology Organisation) contractto develop a new antenna solution thatminimizes antenna detectability by radar. Sincethen, an investigation of the wider technicalissues of existing antenna systems has revealedareas where plasma antennas might be useful.The project attracts the interest of theindustrial groups involved in such diverse areasas fluorescent lighting, telecommunicationsand radar. Plasma antennas have a number of potential advantages for antenna design.

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When a plasma element is not energized, it isdifficult to detect by radar. Even when it isenergized, it is transparent to thetransmissions above the plasma frequency,which falls in the microwave region. Plasma

elements can be energized and de-energized inseconds, which prevents signal degradation.When a particular plasma element is notenergized, its radiation does not affect nearbyelements. HF CDMA Plasma antennas will havelow probability of intercept( LP) and lowprobability of detection( LPD ) in HFcommunications.

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Plasma A ntenn a T echno logySince the discovery of radio frequency ("RF")transmission, antenna design has been anintegral part of virtually every communicationand radar application. Technology hasadvanced to provide unique antenna designsfor applications ranging from generalbroadcast of radio frequency signals for publicuse to complex weapon systems. In its mostcommon form, an antenna represents aconducting metal surface that is sized to emitradiation at one or more selected frequencies.Antennas must be efficient so the maximumamount of signal strength is expended in the

propogated wave and not wasted in antennareflection.Plasma antenna technology employs ionizedgas enclosed in a tube (or other enclosure) asthe conducting element of an antenna.