[SI-LIST] Re: Open Termination
- From: Geoff Stokes <gstokes@xxxxxxxxx>
- To: 'Sitar Moniker' <si_monkey2@xxxxxxxxx>
- Date: Thu, 16 Sep 2004 09:19:31 +0100
Sitar
We have a multi-dimensional problem. It think you are trying to restrict it
to just V and I or E and H. Remember, you have Ex Ey Ez Hx Hy and Hz to
think about.
But this is turning into a full-scale tutorial. Eventually we all have to
go back to our books and I think it's time to close this discussion. Try
Bleaney and Bleaney "Electricity and Magnetism" (OUP). Read the chapter on
Filters, Transmission lines and Waveguides referring back to earlier
chapters for understanding. You might learn something from surfing the web,
but generally you will find many incomplete discussions, and this
undergraduate text is much more secure.
Best wishes
Geoff
-----Original Message-----
From: Sitar Moniker [mailto:si_monkey2@xxxxxxxxx]
Sent: 15 September 2004 17:24
To: Geoff Stokes
Cc: si-list@xxxxxxxxxxxxx
Subject: Re: [SI-LIST] Re: Open Termination
Thank you, Geoff. To be specific, let us consider a microstrip line the
load end of which is left open. There are two impedances. One is the
impedance of the line (V/I) and the other, beyond the point where the line
ends, is the impedance of free space (E/H) . The 377 Ohms I mentioned
earlier corresponds to this (E/H). Am I right so far?
If the open termination is modelled with fringing capacitance and possibly
radiation loss, what is the magnitude of this impedance so we could
approximate it with infinity?
V and I on the line are due to propagating E and H waves. Then, what is the
equivalent of a (V/I)=50 Ohms in terms of corresponding (E/H)? What is the
equivalent of (E/H)=377 Ohms in terms of (V/I)?
If ideal open circuit approx (Vi=Vr) is good especially at lower
frequencies, why do we routinely use it at higher frequencies as well? Is
there a somewhat realistic model for open termination?
Geoff Stokes <gstokes@xxxxxxxxx> wrote:
Sitar
In addition to your modern engineering books, you also need a classical book
on electricity and magnetism or microwave/rf engineering. This will show
that:
1. Impedance of a wave in free medium (e.g. air) is not the impedance of a
transmission line. One is E/H, the other is V/I.
2. Open termination is not infinite impedance and is sometimes modelled
with fringing capacitance and possibly radiation loss.
3. For the ideal open circuit (which does not exactly exist as I just said,
but sometimes it's good enough for an approximate analysis, especially at
lower frequencies), the incident wave voltage, Vi amplitude is equal to the
reflected wave amplitude, and in phase with it. So the total at the open is
2Vi. At some other point on the line, the phases are different, and so you
will plot a standing wave.
Good luck
Geoff
> -----Original Message-----
> From: Sitar Moniker [mailto:si_monkey2@xxxxxxxxx]
> Sent: 14 September 2004 22:48
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Open Termination
>
>
> In SI and HSDD books, they assume that open termination
> offers infinite impedance. My understanding is open end line
> is exposed to air which has about 377 ohms.
>
> 1) How do you get infinite impedance for unterminated line?
>
> 2) Is there any intuitive way to show that voltage at the
> open end doubles- other than using math: ref. coeft. = +1?
>
> __________________________________________________
> Do You Yahoo!?
> Tired of spam? Yahoo! Mail has the best spam protection around
> http://mail.yahoo.com
>
> ------------------------------------------------------------------
> 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:
> //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:
> //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
>
>
_________________________________________________________
Zetex Semiconductors - Solutions for an analog world
http://www.zetex.com
_________________________________________________________
######################################################################
E-MAILS are susceptible to interference. You should not assume that
the contents originated from the sender or the Zetex Group or that they
have been accurately reproduced from their original form.
Zetex accepts no responsibility for information, errors or omissions in
this e-mail nor for its use or misuse nor for any act committed or
omitted in connection with this communication.
If in doubt, please verify the authenticity with the sender.
######################################################################
------------------------------------------------------------------
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:
//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:
//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
_____
Do you Yahoo!?
Yahoo!
<http://us.rd.yahoo.com/mail_us/taglines/virus/*http://promotions.yahoo.com/
new_mail/static/protection.html> Mail - Helps protect you from nasty
viruses.
_________________________________________________________
Zetex Semiconductors - Solutions for an analog world
http://www.zetex.com
_________________________________________________________
######################################################################
E-MAILS are susceptible to interference. You should not assume that
the contents originated from the sender or the Zetex Group or that they
have been accurately reproduced from their original form.
Zetex accepts no responsibility for information, errors or omissions in
this e-mail nor for its use or misuse nor for any act committed or
omitted in connection with this communication.
If in doubt, please verify the authenticity with the sender.
######################################################################
------------------------------------------------------------------
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:
//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:
//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:
