Antennas
Electromagnetic Radiation
The magnetic field lines are in red
The electric field lines are in blue
The inductance and capacitance (together with the implied excitation
energy)
comprise a tuned circuit. This dynamic representation above depicts
electromagnetic radiation illustrating how the plates of a capacitor relate
to the elements of a dipole antenna. Not shown is the wave nature of
the radiation fields and their 90° relationship to each other.
The electric and magnetic energy in an electromagnetic
wave are in phase with each other and polarized at ninety degrees to each
other with the electric field being vertically polarized, and the magnetic
field horizontal in these graphic examples.
Below are shown the vertical electric field (blue) and the
horizontal magnetic field (red) with
their magnitudes varying sinusoidally with time on the X axis.
Above
is a dynamic illustration of the magnetic and electric fields shown in the
static image above it (albit with the colors reversed).
Above is another dynamic illustration of the magnetic and electric fields of
an electromagnetic wave.
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The above picture shows how several quantities on and near a half-wave
dipole vary in the course of time. These quantities are indicated by
different colors, as follows:
Currents: indicated by blue lines,
with length proportional to the magnitude.
Charges: indicated by
cyan and
magenta square around the wire on which the charge is
"sitting". The size of the square represents the magnitude, the color
the sign: cyan for positive, magenta
for negative charge.
Electric field vectors: indicated by
red lines.
Magnetic field vectors: indicated by
green lines.
The dipole antenna itself is on the Y axis, in the bottom left corner of
the picture. The electric and magnetic field strength has only
been calculated in the first quadrant of the YZ plane. Because of
symmetry, extending the calculation to other quadrant positions would
not add anything significant to visualizing the fields. Although
this is not immediately obvious from the picture, the electric field
vectors lie in the YZ plane, while the magnetic field is perpendicular
to that plane.
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From this page you can view the antennas currently in use
at station KJ6YVT by clicking on the links on the right menu below.
The SWR plots on the antenna pages were created with the
LP-Plot utility program kindly provided by Larry Phipps, manufacturer of
the LP-100A digital vector wattmeter.
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