[SI-LIST] Re: Discontinuities on PCB

Hello Ivan,
 
using HFSS, I followed your illustrative method step-by-step and obtained just 
the results I have been hoping for, but couldn't get for almost a year. I 
searched almost everywhere for related publications and tried all I could, but 
remained frustrated. Thanks a lot for your invaluable help. I think many people 
in this list also leant from your very comprehensive mail (online lecture).
I will be greateful if you could send me your publication on discontinuities 
immediately it is available. 
 
Thanks
Charles
Ivan Ndip <ndip@xxxxxxxxxxxxxxxxx> wrote:
Hello Charles,

I have been working on RF/microwave modeling and analysis of 
discontinuities in chip packages and boards for quite some time now, so 
I think I can share my experience with you.
Most of the contributions made so far on microstrip discontinuities, 
especially by Silvester, Benedek, Itoh, Gopinath, Thompson etc. in the 
1970s, centered around the calculation of discontinuity capacitance and 
inductance using quasi-static methods. So, concentrating only on these 
publications won't help you know how far away from the discontinuity the 
excited higher-order modes can go. However, Menzel, Mehran, Kompa and 
Wolf published quite a lot also in the 70's on the calculation of 
frequency-dependent properties of microstrip discontinuities.
I suggest that you first of all go through these publications in order 
to fully well understand what happens in a discontinuity. (Dr. Ronald De 
Smedt already gave a very good explanation of the phenomenon).

Secondly, you must also note that the number and characteristics of 
higher-order modes excited don't depend only on frequency (as you think) 
but also on the geometry of the discontinuity under consideration (don't 
expect a via and bend to excite same higher-order modes). However, since 
these modes are evanescent (this is mostly the case for discontinuities 
in chip packages and PCBs used for RF/high-speed applications), they 
attenuate rapidly from the discontinuity. (Note: use either Hoffmann's 
Handbook on MIC or Microstrip Lines and Slotlines by Gupta et al. to 
calculate the cut-off frequency in your case). To define the precise 
distance away from the discontinuity that these modes can go, you need a 
3D full-wave solver (e.g., HFSS) to compute the field behavior in the 
vicinity of the discontinuity. I would suggest you excite only one mode 
(certainly the fundamental mode) and from the extracted S-parameters you 
can study the mode conversion that occurred. Repeat the experiment for 
different lengths of line interconnecting the wave port and the 
discontinuity. You'll realize that in the immediate vicinity of the 
discontinuity, the magnitude of the considered S-parameter (at a 
particular frequency), computed from the fundamental mode changes very 
rapidly. This can be attributed to the presence of the fields of 
higher-order modes which are still very strong. But with increasing 
distance away from the discontinuity, the magnitude of the S-parameter 
slowly converges to a particular value, because these fields vanish, 
leaving the fundamental mode unperturbed. The point away from the 
discontinuity where the magnitude of your S-parameter becomes constant 
or changes by less than a self-defined value (e.g., 5% or so) defines 
the end or insignificance of the higher-order modes. I call it the end 
of the "discontinuity effect".

Certainly you have to take into consideration the S-parameters of the 
line used. But from my experience, the variation of the magnitude of 
S-parameters in the vicinity of the discontinuity is essentially due to 
the excited higher-order modes, especially when you consider S11.

I'll be presenting a paper at the 35th European Microwave Conference 
(European Microwave Week - Oct. 3-7, 2005) in Paris entitled "Efficient 
RF/Microwave Modeling of Discontinuities in Chip Packages and Boards". I 
strongly recommend you also go through this paper, when available.

Regards,
Ivan Ndip







Charles Harrington wrote:

>Hello Mark,
>
>because Eric's book is so beautifully written, I've
>gone through it almost twice already. However, it has
>very little or nothing to do with my question. I also
>went through Johnson's book (Advanced Black Magic),
>Silvester and Benedek?s publications on discontinuties
>and quite a lot of other electromagnetic texts. So,
>it's not a question for beginners.
>Jose recommended me Gupta's book (thanks Jose), which
>I already read. Here, Wolf and Mehran's waveguide
>model are used to analyze T-bends, Gap and other
>discontinuities, but the questions on how far the
>excited modes go away from the discontinuity and how
>this depend on the frequency are not dealt with. 
>As far as I know, this subject has not being properly
>dealt with yet. 
>So may the gurus recommend any other publications on
>this subject or some advice. 
>
>Thanks,
>Charles
>
> 
>
>
>
>
> 
>


-- 
***************************************************************************
Dipl.-Ing. Ivan Ndip
Research Engineer

Fraunhofer Institut für Zuverlässigkeit und Mikrointegration (FhG-IZM)
Dept.: Advanced System Engineering (ASE)
Gustav-Meyer-Allee 25
D-13355 Berlin
Germany

Phone: +49 (0) 30 46403 679
Fax: +49 (0) 30 46403 158

E-mail: ndip@xxxxxxxxxxxxxxxxx | Web: http://www.izm.fraunhofer.de
ndip@xxxxxxxx
***************************************************************************

Diese E-Mail kann Betriebs- und Geschäftsgeheimnisse, dem Anwaltsgeheimnis
unterliegende oder sonstige vertrauliche Informationen enthalten. Sollten
Sie diese E-Mail irrtümlich erhalten haben, ist Ihnen die Kenntnisnahme des
Inhalts, eine Vervielfältigung oder Weitergabe der E-Mail ausdrücklich
untersagt. Bitte benachrichtigen Sie den Absender der E-Mail und vernichten
die empfangene E-Mail. Vielen Dank.

Since this e-mail contains confidential information, it must be treated with
utmost confidentiality. Any person who may get in contact with this
information by mistake should not take any notice of the topic and should
not pass on or duplicate any part of this information. The e-mail has to be
destroyed and the sender of the e-mail has to be informed immediately.
Thank you.




------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field

or to administer your membership from a web page, go to:
http://www.freelists.org/webpage/si-list

For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field

List FAQ wiki page is located at:
http://si-list.org/wiki/wiki.pl?Si-List_FAQ

List technical documents are available at:
http://www.si-list.org

List archives are viewable at: 
http://www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu



                
---------------------------------
Yahoo! Mail Mobile
 Take Yahoo! Mail with you! Check email on your mobile phone.

------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field

or to administer your membership from a web page, go to:
http://www.freelists.org/webpage/si-list

For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field

List FAQ wiki page is located at:
                http://si-list.org/wiki/wiki.pl?Si-List_FAQ

List technical documents are available at:
                http://www.si-list.org

List archives are viewable at:     
                http://www.freelists.org/archives/si-list
or at our remote archives:
                http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
                http://www.qsl.net/wb6tpu
  

Other related posts: