RE: [SI-LIST] : MECL System Design Handbook

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From: Dan Swanson (DSWANSON@BartleyRF.com)
Date: Thu May 10 2001 - 10:24:19 PDT


Chris, Lee and all:

Here is some info on return loss (reflection coefficient)
for bends and mitered bends. This happens to be for
a ceramic substrate. Relative improvement will be the
same for PC board materials. PC board bend may start
out worse, w/h ratio will be greater for the lower dielectric
constant.

If someone wants to send me some typical dimensions of
interest, I might have time to run it on the field-solver.

 <<bends.pdf>>
PDF file is two pages from my course notes.

Dan

Dan Swanson EMAIL: d.swanson@ieee.org
Bartley RF Systems, Inc. TEL: 978-834-4085
37 South Hunt Road FAX: 978-388-7077
Amesbury, MA 01913

> -----Original Message-----
> From: Chris Padilla [SMTP:cpad@cisco.com]
> Sent: Thursday, May 10, 2001 12:46 PM
> To: si-list@silab.eng.sun.com
> Subject: Re: [SI-LIST] : MECL System Design Handbook
>
> Lee,
>
> It is not a myth, there is "some kind of effect" from right angle bends.
>
> The real question is, I believe, "Do I care, given the speed and/or
> frequency content of the signals I am dealing with?"
>
> For most of us right now, on this list, we probably *should not* care as
> you point out.
>
> If one is designing a 50 GHz antenna, then it might make a world of
> difference!
>
> Out of curiosity, what kind of rise time were you pushing through that
> right angle bend? 100 ps? I am farily certain that I've seen some small
> dips (aka capacitance) through right angle bends but I cannot honestly say
>
> that it was directly attributed to the bend.
>
> Thanks----->Chris
>
> >Any of you who want to know how the myth about right angle bends got
> >started, look
> >at figure 7.17 on page 155. This alleges that right angle bends can be
> >seen by a
> >TDR. I've done this measurement dozens of times and coiuld never see a
> right
> >angle bend.
> >
> >A few years ago, I called Mr. Blood the author of the book and asked
> >about the
> >diagram. His reply was that he knew the diagram was flawed, but there
> >wasn't time
> >to fix it before the book went to press.
> >
> >As a result, thousands of engineers have spend countless time worrying
> >about right
> >angle bends.
> >
> >When we publish technical information such as this, it is important to
> >insure it
> >is accurate.
> >This applies especially to applications notes, whic often contain
> entirely
> >false
> >data.
> >
> >Lee
>
>
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