to go go to our main page on VSWR
New for March 2008! We
now offer an Excel spreadsheet that will help you visualize how
voltage standing waves are created. It's located in our
download area. Note: you have to enable macros in order
for the spreadsheet to work!
The hypothetical phenomenon we
are trying to illustrate is as follows. A TEM transmission line
of impedance Z1 is connected to a second transmission line of impedance
Z2 (think of this as two coax lines in series, we'll add a figure
one of these days). The discontinuity occurs at the value X=25 (whatever
units you like). The Z2 transmission line is terminated in a matched
load (perfect resistor of value R=Z2) so that there is no additional
reflection down the line. The waveforms represent intensity (and
polarity) of the electric field, which is entirely perpendicular
to the direction of propagation (that's what TEM, or transverse
The two charts below are snapshots
in time. On the first chart, the composite wave on the left (forward
plus reflected, color red) has peaks around 2, 8, 14 and 20. These
are the maxima along the standing wave (and later there are other
maximum between these points at 5, 11 and 17).
You'll also not that the composite
waveform on the left is contiguous with the transmitted waveform
on the right of the mismatch (blue line). This has to be the case,
it is not possible to have a discontinuity in the electric field.
The chart below the composite
wave is at the minima located at 0, 6, 12 and 18. Note there are
other minima between these at 3, 9 and 15.
These images are nothing compared
to seeing the waveform move before your eyes, with your mouse controlling
the speed. Go get the download