Animation of a half-wave dipole antenna transmitting radio waves, showing the electric field lines. The dipole, in the center, consists of two vertical metal rods with an alternating current at its resonant frequency applied at its center from a radio transmitter (not shown) The voltage alternately charges the two ends of the antenna positive (+) and negative (−). Standing waves of current (red arrows) flow up and down the rods. The alternating voltage on the rods creates loops of electric field (black lines) that pinch off into closed loops and radiate away from the antenna at the speed of light. These are the radio waves. The radiated power is greatest in the horizontal direction, perpendicular to the antenna, and decreases to zero above and below the antenna, on the antenna axis. This picture only shows the electric field in a single plane through the antenna axis; the field is actually axially symmetrical about the antenna. The action is shown slowed down drastically in this animation; real radio waves oscillate at rates of thirty thousand to a billion cycles per second.