Re: [SI-LIST] : Re: Antenna Problem on the Board

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From: Sainath Nimmagadda (sainath@lsil.com)
Date: Fri May 25 2001 - 16:50:42 PDT


Hi Doug,

Please see below:

Doug McKean wrote:

> subramanya wrote:
> >
> >
> > Hello SI Gurus,
> > I have a basic question here. We all know
> > that "Right angled traces are never used
> > on PCBs" as the act as antennas (better
> > antennas than the curved traces). In an
> > article I read that this radiation is due
> > not to the frequency of the signal , but
> > to it's rise time. Could someone please
> > explain me this theory ?
>
> The answer is yes and no.
>
> Yes, because theoretically, bending a conductor
> will make it radiate. This comes from the
> Laplacian taken from Maxwell which shows that
> acceleration of charge is required for radiation.
>

Do you have a book or other reference in mind as you connect Laplacian,
Maxwell and a conducting bend?

Thanks,
Sainath

>
> But, what some people forget is that this is in
> a vectorial sense as well. So, by changing the
> direction of an accelerating charge, radiation
> should happen. Fractal antennas make use of this
> effect.
>
> I have actually tried to measure the effects
> of bending various lengths of wire and measuring
> the radiated effects. But because of too many
> variables, I can't conclusively say that bending
> causes any sort of increase in radiation.
> Maybe I should revisit that.
>
> Now, how much does the bending make? I don't know.
> I've personally not seen anything in my lab or
> anyone's lab which would make me positively
> state never use right angles. In my opinion,
> as far as radiation effects go, I don't think
> they really cause that much of a difference.
>
> Now, as far as crosstalk goes, there can be a
> differential-to-common mode transfer mechanism
> going on. Now I've seem many a discussion try
> to reduce the right angle to things such as
> impedance changes, capacitance changes, but
> I think they fall short.
>
> - Doug McKean
>
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