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Curtain arrays are a class of large multielement directional wire radio transmitting antennas, used in the shortwave radio bands. They are a type of reflective array antenna, consisting of multiple wire dipole antennas, suspended in a plane, often in front of a "curtain" reflector made of a flat vertical screen of many long parallel wires.〔 These are suspended by support wires strung between pairs of tall steel towers, up to high.〔 They are used for long-distance skywave (or ''skip'') transmission; they transmit a beam of radio waves at a shallow angle into the sky, which is reflected by the ionosphere back to Earth beyond the horizon. Curtain antennas are mostly used by international short wave radio stations to broadcast to large areas at transcontinental distances.〔 Because of their powerful directional characteristics, curtain arrays are often used in government propaganda radio stations to beam propaganda broadcasts over national borders into other nations. For example, curtain arrays were used by Radio Free Europe and Radio Liberty to broadcast into Eastern Europe. ==History== Curtain arrays were originally developed during the 1920s and 1930s when there was a lot of experimentation with long distance shortwave broadcasting. The underlying concept was to achieve improvements in gain and/or directionality over the simple dipole antenna. In the early 1920s, Guglielmo Marconi, pioneer of radio, commissioned his assistant Charles Samuel Franklin to carry out a large scale study into the transmission characteristics of short wavelength waves and to determine their suitability for long distance transmissions. Franklin invented the first curtain array aerial system in 1924, known as the 'Franklin' or 'English' system. Other early curtain arrays included the Bruce array patented by Edmond Bruce in 1927,〔US Patent no. 1813143, (''Aerial System'' ), E. Bruce, filed Nov 25, 1927, granted July 7, 1931〕 and the Sterba curtain, patented by Ernest J. Sterba in 1929.〔US Patent no. 1885151, ( ''Directive antenna system'' ), E.J. Sterba, filed July 30, 1929, granted November 1, 1932〕 The Bruce array produces a vertically-polarised signal, Sterba arrays (and the later HRS antennas) produce a horizontally-polarised signal. The Sterba array was used by Bell Labs and others during the 1930s and 1940s. The Sterba curtain is however a narrowband design and is only steerable by mechanical means. However, as far back as the mid-1930s, Radio Netherlands was using a rotatable HRS antenna for global coverage. Since the 1950s the HRS design has become more or less the standard for long distance high power shortwave broadcasting (> 1000 km). Curtain arrays were used in some of the first radar systems, such as Britain's Chain Home network. During the Cold War, large curtain arrays were used by the Voice of America, Radio Free Europe, and Radio Liberty, and analogous Western European organizations, to beam propaganda broadcasts into communist countries, which censored Western media. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Curtain array」の詳細全文を読む スポンサード リンク
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