File:Dipole Antenna Standing Waves Animation 6 - 5fps.gif
The blue arrows show the direction of conventional current, flow of positive charge. The electrons oscillating back and forth in the antenne move in a direction opposite to the arrows. The action is shown slowed down enormously; the currents in an actual antenna oscillate back and forth 20 thousand to one billion times per second.
This image differs from my previous animation Dipole antenna standing waves animation 1-10fps.gif and most graphs of the standing waves shown in antenna textbooks in that it shows the effect of the driving voltage on the standing waves. The transmission line applies a voltage between the two antenna elements, driving the oscillations. The energy from this current provides the energy lost in the antenna' s radiation resistance which represents the energy radiated as radio waves. Since the antenna is fed at its resonant frequency, the input voltage is in phase with the current (blue bar), so the antenna presents a pure resistance to the feedline. Dipoles have relatively high Q factor so the amount of energy stored in the standing waves is large compared to the energy added each cycle by the feedline, the feed voltage just represents a small perturbation to the standing waves. This is why the voltage standing wave is much larger than the voltage step at the feedline. Since the standing waves are storing energy, not transporting power, the current in them is not in phase with the voltage but 90° out of phase
This image differs from my previous animation Dipole antenna standing waves animation 1-10fps.gif and most graphs of the standing waves shown in antenna textbooks in that it shows the effect of the driving voltage on the standing waves. The transmission line applies a voltage between the two antenna elements, driving the oscillations. The energy from this current provides the energy lost in the antenna' s radiation resistance which represents the energy radiated as radio waves. Since the antenna is fed at its resonant frequency, the input voltage is in phase with the current (blue bar), so the antenna presents a pure resistance to the feedline. Dipoles have relatively high Q factor so the amount of energy stored in the standing waves is large compared to the energy added each cycle by the feedline, the feed voltage just represents a small perturbation to the standing waves. This is why the voltage standing wave is much larger than the voltage step at the feedline. Since the standing waves are storing energy, not transporting power, the current in them is not in phase with the voltage but 90° out of phase
Dipole antenna standing waves animation 1-10fps.gif - less detail
Dipole antenna standing waves animation 6-10fps.gif - faster frame rate