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Plasma antenna
A plasma antenna is a type of radio antenna currently in development in which plasma is used instead of the metal elements of a traditional antenna.〔('Stealth' Antenna Made Of Gas, Impervious To Jamming ) science20.com, published 2007-11-12, accessed 2010-12-14〕 A plasma antenna can be used for both transmission and reception.〔(Plasma Antenna ) Center for Remote Sensing, accessed 2010-12-14〕 Although plasma antennas have only become practical in recent years, the idea is not new; a patent for an antenna using the concept was granted to J. Hettinger in 1919.〔(Aerial Conductor for Wireless Signaling and Other Purposes ) United States Patent 1309031, published 1919-07-08, accessed 2010-12-15〕
Early practical examples of the technology used discharge tubes to contain the plasma and are referred to as ionized gas plasma antennas. Ionized gas plasma antennas can be turned on and off and are good for stealth and resistance to electronic warfare and cyber attacks. Ionized gas plasma antennas can be nested such that the higher frequency plasma antennas are placed inside lower frequency plasma antennas. Higher frequency ionized gas plasma antenna arrays can transmit and receive through lower frequency ionized gas plasma antenna arrays. This means that the ionized gas plasma antennas can be co-located and ionized gas plasma antenna arrays can be stacked. Ionized gas plasma antennas can eliminate or reduce co-site interference. Smart ionized gas plasma antennas use plasma physics to shape and steer the antenna beams without the need of phased arrays. Satellite signals can be steered and/or focused in the reflective or refractive modes using banks of plasma tubes making unique ionized gas satellite plasma antennas. The thermal noise of ionized gas plasma antennas is less than in the corresponding metal antennas at the higher frequencies.〔 Solid state plasma antennas (also known as plasma silicon antennas) with steerable directional functionality that can be manufactured using standard silicon chip fabrication techniques are now also in development.〔(Wireless at the speed of plasma ) New Scientist, published 2010-12-13, accessed 2010-12-14〕 Plasma silicon antennas are candidates for use in WiGig (the planned enhancement to Wi-Fi), and have other potential applications, for example in reducing the cost of vehicle-mounted radar collision avoidance systems.〔
==Operation==
In an ionized gas plasma antenna, a gas is ionized to create a plasma. Unlike gases, plasmas have very high electrical conductivity so it is possible for radio frequency signals to travel through them so that they act as a driven element (such as a dipole antenna) to radiate radio waves, or to receive them. Alternatively the plasma can be used as a reflector or a lens to guide and focus radio waves from another source.〔(Plasma Antennas: Survey of Techniques and the Current State of the Art ) D C Jenn, published 2003-09-29, accessed 2010-10-15〕
Solid-state antennas differ in that the plasma is created from electrons generated by activating thousands of diodes on a silicon chip.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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