The result is:
TD = 1000 x .002 x 10-6 seconds
or
TD = 2 microseconds
c. This example shows that the use of real line to delay a pulse 2
microseconds would be awkward to say the least. Even if you roll the 1,000
feet of transmission line to coil form, it will be very bulky.
If you
wanted to increase the delay, you would have to make the line even longer.
You could not change the L and C without making the line longer because
these are characteristics of the line. With artificial transmission lines,
it's a different story.
An ATL can be built to occupy a small space and
still have the same characteristics as several miles of real transmission
line. In other words, a combination of L and C components (ATL) can be used
to obtain the same time delay as that provided by a real transmission line
of any given length.
5.
An ATL can be substituted for a real line.
a. The time delay you get from an ATL depends upon the lumped values of
inductance and capacitance per section and the number of sections used.
b. To find the time delay of an ATL, multiply the square root of the L
and C per section by the number (N) of sections used, using the formula:
TD =
. One coil and capacitor can be used instead of many feet of line.
To increase the delay, merely increase the values of L and C, or add more
sections. Three to eight sections are used for most radar applications.
6.
Comparing characteristics.
So far, you have learned that artificial transmission lines can be
used as substitutes for real transmission lines for certain applications in
radar and other RF systems.
The major uses of ATL are as pulse-forming
lines and delay lines.
ATL have the same characteristics as real
transmission lines.
A comparison of the characteristics is given as a
summary in Figure 25.
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