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- In radio systems, many different antenna types are used whose properties are especially crafted for particular applications. Antennas can be classified in various ways. The list below groups together antennas under common operating principles, following the way antennas are classified in many engineering textbooks.
* The dipole, monopole, array, and large loop antenna types discussed below typically function as resonant antennas; in resonant antennas, waves of current and voltage bounce back and forth between the ends, or circulate around a closed loop, and their overlapping sections add and subtract to form standing waves along the elements.
* Traveling wave antennas are not resonant: Their current and voltage waves travel in one direction along the antenna elements and then are absorbed by a resistor.
* Aperture antennas are made of an outer, surrounding reflective surface whose shape concentrates waves striking it onto a small inner antenna; the inner antenna can be either resonant or non-resonant. (en)
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