Coplanar Waveguide - RF Cafe Forums
Post subject: coplanar waveguide Posted: Tue Dec 05,
2006 2:11 pm
Joined: Tue Dec 05, 2006
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
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.
Post subject: Posted: Tue Dec 05, 2006 3:41 pm
Joined: Mon Jun 27, 2005 2:02 pm
I will try to answer on your
. will this system be well described
using the telegraphist equations?
The telegraphist equations
define any transmission line, doesn't matter of which kind.
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
This site contains a lot of useful information
Post subject: Posted: Wed Dec 06, 2006 8:14
Joined: Tue Dec 05, 2006 1:55 pm
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
Post subject: Posted: Thu Dec 07, 2006
Joined: Mon Jun 27, 2005 2:02
Why not trying to use
a EM solver to find out these parameters?
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.
Post subject: Posted: Thu Dec 07, 2006 5:07
Joined: Tue Dec 05, 2006 1:55 pm
Thank you very much, now is clear what to do, I'll
use what you suggest.