From: Jason Leung ([email protected])
Date: Mon May 28 2001 - 06:07:20 PDT
Hi all:
I kind of know why the radiation is higher with higher impedance and
lower with lower impedance.
The reason is you can picture the transmission line impedance as
Z=sqrt(L/C) , so if you decrease the thickness of the substrate between
the ground and trace ,the capacitance will also be increased and in turn
the impedance will decrease proportionally .Moreover, since the
thickness is smaller , the trace is more coupled to the
ground ,and that strong coupling effect can helps you to reduce the
radiation effects. The opposite is true for the higher impedance case.
So if ones wanted to reduce the crosstalk effect ,he can use lower
impedance transmission line .
Hope that will be helpful to you
Regards
Jason Leung
[email protected] wrote:
> Ron,
> you have touched on a question that has been with me for several
> years, and
> that question is how do I minimize transmission line radiation. I
> noticed in
> an earlier thread (different subject) that higher impedance lines
> radiated
> more than lower impedance lines. I don't understand why this is
> true. It
> seems to me that a lower Z line, if excited by the same voltage, would
>
> radiate more due to having a higher current in the line. Also, by the
> same
> reasoning, I thought that a source terminated line would radiate less
> that a
> parallel (at the receiver) terminated line, since only half of the
> current
> and voltage would be required to get a full signal swing at the
> receiver (+1
> reflection coefficient). Your statements seem to indicate that
> reflections
> caused by impedance mismatches are the primary causes of
> radiation--this
> means that a parallel terminated line is much superior to a source
> terminated
> line where radiation is concerned. Please help me get a better
> understanding
> of these fundamentals. I would also like to know how you employ the
> trig.
> Richard Ellison
> 972-569-8317
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