Animation showing a half-wave <a href="https://en.wikipedia.org/wiki/dipole_antenna" class="extiw" title="w:dipole antenna">dipole antenna</a> receiving power from a <a href="https://en.wikipedia.org/wiki/radio_wave" class="extiw" title="w:radio wave">radio wave</a>.  The antenna consists of two metal rods each one-quarter of the <a href="https://en.wikipedia.org/wiki/wavelength" class="extiw" title="w:wavelength">wavelength</a> long, attached through a parallel transmission line to a resistance <i>R</i> equal to the <a href="https://en.wikipedia.org/wiki/characteristic_impedance" class="extiw" title="w:characteristic impedance">characteristic impedance</a> of the antenna, representing the receiver.  The electromagnetic wave is represented by its <a href="https://en.wikipedia.org/wiki/electric_field" class="extiw" title="w:electric field">electric field</a>  <i>(<span style="color:green;">E, green arrows</span>)</i> (it should be kept in mind that the drawing only shows the field along one line, while the radio wave is actually a plane wave and the electric field is actually the same at every point on a plane perpendicular to the direction of motion).  The wave's magnetic field is not shown.<br><br>   
The oscillating electric field exerts force on the <a href="https://en.wikipedia.org/wiki/electron" class="extiw" title="w:electron">electrons</a> in the antenna rods , causing them to move back and forth in <a href="https://en.wikipedia.org/wiki/electric_current" class="extiw" title="w:electric current">currents</a> <i>(black arrows)</i> between the ends of the antenna rods, charging the ends of the antenna alternately positive <i>(+)</i> and negative <i>(−)</i>.    Since the antenna is a half-wavelength long at the radio wave's frequency, it excites <a href="https://en.wikipedia.org/wiki/standing_wave" class="extiw" title="w:standing wave">standing waves</a> of <a href="https://en.wikipedia.org/wiki/voltage" class="extiw" title="w:voltage">voltage</a> <i>(<span style="color:red;">V, red</span>)</i> and current in the antenna. The voltage along the antenna elements is represented graphically by a band of red whose thickness at any point is proportional to the magnitude of the voltage.  The oscillating currents flowing back and forth from one antenna element to the other, pass down the transmission line and through the radio receiver, represented by <i>R</i>.  In this animation the action is shown slowed down drastically; the radio waves received by dipoles actually oscillate back and forth at tens of thousands to billions of cycles per second.
<a href="//commons.wikimedia.org/w/index.php?title=User:Chetvorno&amp;action=edit&amp;redlink=1" class="new" title="User:Chetvorno (page does not exist)">Chetvorno</a>
2015-06-07
<span class="int-own-work" lang="en">Own work</span>