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The first smart antennas were developed for military communications and intelligence gathering. The growth of cellular telephone in the 1980s attracted interest in commercial applications. The upgrade to digital radio technology in the mobile phone, indoor wireless network, and satellite broadcasting industries created new opportunities for smart antennas in the 1990s, culminating in the development of the MIMO (multiple-input multiple-output) technology used in 4G wireless networks. == Directional antennas == The earliest success at tracking and controlling wireless signals relied on the antennas’ physical configuration and motion. The German inventor and physicist Karl F. Braun demonstrated beamforming for the first time in 1905. Braun created a phased array by positioning three antennas to reinforce radiation in one direction and diminish radiation in other directions. Guglielmo Marconi experimented with directional antennas in 1906. Directional antennas were rotated to detect and track enemy forces during World War I. The British admiralty used goniometers (radio compasses) to track the German fleet. Edwin H. Armstrong invented the superheterodyne receiver to detect the high frequency noise generated by German warplanes’ ignition systems. The war ended before Armstrong’s creation was ready to help direct antiaircraft fire. Multiple elements (a fed dipole, a director, and reflectors) were assembled in the 1920s to create narrow transmit and receive antenna patterns. The Yagi-Uda array, better known as the Yagi antenna, is still widely used.〔 Edmond Bruce and Harald T. Friis developed directional antennas for shortwave and microwave frequencies during the 1930s.〔 AT&T’s decision to use microwave to carry inter-city telephone traffic led to the first large-scale commercial deployment of directional antennas (based on Friis’ horn reflector design) in 1947. Directional antennas with alternating polarization enabled a single pair of frequencies to be reused over many consecutive hops. Microwave links are less expensive to deploy and maintain than coaxial cable links. 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「History of smart antennas」の詳細全文を読む スポンサード リンク
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