[SI-LIST]
- From: "Jan Vercammen" <jan.vercammen.jv1@xxxxxxxxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Tue, 30 Apr 2002 10:12:29 +0200
Dear si-list,
I would like to react to Ched-Chang Chai question concerning radiation from
bends in
printed circuit tracks.
I have done TDR measurements and the conclusion is, as everybody elses
conclusion, that
the bends are very hard to see, except at very high frequencies. I tested
with a rise time of 100ps
and it was not possible to see any difference at all!
The radiation from bends is harder but it has been studied numerically and
has been measured! The
results have been reported in the IEICE transactions (Japanese IEEE) and
later in the IEEE trans on EMC. The
paper in the IEICE is publically available:
http://search.ieice.org/2001/pdf/e84-b_9_2604.pdf
The IEICE is at http://www.ieice.org/eng/index.html
Radiation from bend transmission lines
Sungkyu LEE, Masashi HAYAKAWA, Naomitu ISHIBASHI
Vol.E84-B No.9 p.2604
They present a figure (figure 2) that presents power loss (=radiated power) in
function of line height
over lambda (h/lambda) and for different angles at a frequency of 1GHz. Note
that 90 degrees is not
the worst case. There are also other concerns about radiation patterns between
the various configurations.
Check out the article.
Because most microstrip lines have very small h/lambda the radiation from bends
is very small. Actually the
increase for practical tracks on PCBs is negligible and likely less than 1% (or
even smaller), even for high
frequencies
Assume, as an example, that a bend has a 10% higher radiation loss than a
straight wire.
To make things easier assume that the radiated power is emitted isotropically
than the
far-field electric field is proportional to square root of the radiated power.
So a bend produces an
electric field that is about 5% higher or only 0.4dB. Again, for most practical
stuff the 10% used here
is much to high.
A (carefull) conclusions is that radiation from bends is not an issue, much
the same as for signal
integrity (see Doug's article). Except, of course if your doing very high
speed stuff, possible in
combination with high h/lambda.
Kind regards,
Jan Vercammen
PCB/EMC engneering Agfa-Gevaert Belgium
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