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coplanar waveguide - RF Cafe Forums
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cubeleg
Post subject: coplanar waveguide Posted: Tue Dec 05, 2006
2:11 pm
Lieutenant
Joined: Tue Dec 05, 2006 1:55
pm
Posts: 3
Hi!
We are trying to calculate the characteristic
impedance and the speed of light in a coplanar waveguide (CPW), which
has been loaded placing a material in the top of the CPW. I have several
questions about how to calculate this parameter with a network analyzer,
the most important are the following:
i. will this system be
well described using the telegraphist equations?
ii. how
can I extract the scattering matrix of the system CPW-loaded CPW-CPW
without the effect of connectors? We have a calibration kit and we are
able to get rid of the wires which are carrying the signal to the CPW,
but not the connectors.
If someone can give me a reference where
I can find the basics of CPW would be great.
Thanks!
Cubeleg
Top
IR
Post subject: Posted: Tue Dec 05, 2006 3:41
pm
Site Admin
Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373
Location: Germany
I will try to answer on your questions:
Quote:
. will this system be well described using the telegraphist
equations?
The telegraphist equations define any transmission
line, doesn't matter of which kind.
Quote:
ii. how can I
extract the scattering matrix of the system CPW-loaded CPW-CPW without
the effect of connectors? We have a calibration kit and we are able
to get rid of the wires which are carrying the signal to the CPW, but
not the connectors.
I would use a known reference plane like
a known length transmission line, measure its properties, i.e. full
S-parameters. Then add the connector and measure again the same. This
should give you in detail the delta caused by the addition of the connector.
Do these tests at the same frequency in which you measure the CPW
structure.
This site contains a lot of useful information and
applets:
http://www.amanogawa.com/transmission.html
_________________
Best regards,
- IR
Top
cubeleg
Post subject:
Posted: Wed Dec 06, 2006 8:14 pm
Lieutenant
Joined:
Tue Dec 05, 2006 1:55 pm
Posts: 3
Thank you for the answers and
the link, they clarify what we are trying to do.
But I have
to complete my first question, because the telegraphist equations state
the behavior of a transmission line. I understand that the material
placed in the top will change the Z and the electrical lenght of the
loaded line, due to the change in the effective permittivity-permability,
then the scattering of the CPW are different, but, will the step in
the CPW, or other geometric factor, modify the scattering parameters
at the interface CPW-loaded CPW?
I ask this because we are trying
to recover the Z and electrical lenght of the loaded line, in order
to characterize the electromagnetic parameters of a material, but applying
the same equations that we use to recover this factors in a coaxial
line filled with different materials, we have no success. I would like
to clarify if equations are the same or I have to worry about more factors.
Thanks for your answers
Cubeleg.
Top
IR
Post subject: Posted: Thu Dec 07, 2006 3:58 am
Site Admin
Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373
Location:
Germany
Why not trying to use a EM solver to find out these parameters?
The telegrpahist equations are valid for the same conditions,
namely for the same substrate, because they are derived from the substrate
parameters: L, R, C, G are the substrate's parameters per given length.
These are the entry parameters for the equations. If you load your CPW
with a different material then the equations for the different material
are different and the total result is different.
If the step
is made from the same substrate as the CPW then you should use the same
parameters in the equations as you used for the CPW.
_________________
Best regards,
- IR
Top
cubeleg
Post subject:
Posted: Thu Dec 07, 2006 5:07 am
Lieutenant
Joined:
Tue Dec 05, 2006 1:55 pm
Posts: 3
Thank you very much, now is
clear what to do, I'll use what you suggest.
Regards
Cubeleg
Posted 11/12/2012
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