CHAPTER 2 - Conveying Power at Radio Frequency
94
Figure 2.9-2 Graphical Representation of ( )
Let us now consider some significant values of (since is fixed for a specific transmission
line and frequency) and see how they affect the impedance of our line.
For , equation (2.9-1) becomes
Which
is fairly obvious since no transmission line would exist.
For , equation (2.9-1) becomes
(
)
(
)
( )
( )
So
we have found that, if a transmission line which is half a wavelength long is placed between
source and load, our transmission line will become transparent. This will be true for every value of
which makes equal to (or an integer multiple of ) and hence ( ) equal to zero. Let us find
the values of for which this is true.
The Equation
above is satisfied when
So if our line length is equal to a multiple of a half wavelength,
, irrespective of !
You may think, "Well splendid then! I'll just make every transmission line in my circuit equal
to a multiple of and I'll be sorted!" Well, not quite! Firstly, depending on your wavelength, this
may make your circuit rather large!
Conquer Radio Frequency
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