Figure 132.
Simple Dipole Antenna.
b. You know that a simple dipole antenna consists of two quarter-wave
conductors spaced a few inches apart in line with each other. When used as
a transmitting antenna, the output of the transmitter feeds to the inside
ends of the two conductors.
When the transmitter is on, current flows in
each conductor. The current flow back and forth in two conductors sets up a
magnetic field around them.
The magnetic field (H) produces an electric
field (E) and the two fields (called the electromagnetic field) radiate into
space. You will recall that the plane of the electric field determines how
the antenna is polarized.
6.
Polarization of a dipole antenna.
a. The electric and magnetic fields radiate from the dipole in the
manner shown in Figure 133.
The magnetic field always surrounds the
conductors and is perpendicular to them; the electric field is parallel to
the conductors.
b. In Part A of Figure 133, the conductors of the dipole are horizontal
to the earth, and so is the electric field.
Therefore, we call this a
horizontally polarized antenna.
The dipole in Part B of Figure 133 is
vertical to the earth, and so is the electric field. Therefore we call this
a vertical polarized antenna.
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