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Animated diagram of a half-wave dipole antenna receiving a radio wave. The antenna consists of two metal rods connected to a receiver R. The electric field (E, green arrows) of the incoming wave pushes the electrons in the rods back and forth, charging the ends alternately positive (+) and negative (−).
In this tutorial, Steve Stearns, K6OIK, explains the basic characteristics of dipoles for transmitting and receiving. Some surprises await as we learn that a dipole’s transmit current distribution is not exactly sinusoidal, and the receive distribution can be entirely different.
Antennas 101 13 The Dipole - 1 •Oldest and simplest form of antenna –“Di” (two) “Pole” (voltage polarity) –Usually 1/2-wavelength long •Similar to a vibrating string’s fundamental –Current maximum in the middle –Voltage maximum at the ends •Pattern repeats every 1/2-wavelength –Direction or amplitude is reversed 2013
In its simplest form, a dipole is an antenna made of wire and fed at its center as shown in Fig 1. (This may look familiar: You may have received a QSL card with a sketched dipole, resembling Fig 1, to denote the antenna the other station used during your contact.)
antenna and counterpoise basics • r.f. transmission/antenna systems have similar qualities to complete proper a.c. & d.c. supply/load circuits. • kirchoff’s law dictates that current flow out through a circuit must equal current returned. thus the r.f. circuit wants to be complete too.
AN91445 explains antenna design in simple terms and provides guidelines for RF component selection, matching network design, and layout design.
The dipole antenna is symmetric when viewed azimuthally (around the long axis of the dipole); as a result the radiation pattern is not a function of the azimuthal angle . Hence, the dipole antenna is an example of an omnidirectional antenna.
