Assuming you are talking about a coplanar waveguides on the surface, there are generally two differences. Using Polar's nomenclature, I think it's called "coplanar waveguide with ground" (CPWG) and the other "coplanar waveguide" (CPW). CPWG has a return plane on an underlying layer, CPW does not. Your initial description is a little misleading as to which you have.

If I remember correctly, the CPWG will be tested in the same fashion as a microstrip since it has a return plane on a layer beneath. For the CPW where no return plane is underneath, you will need to test using the adjacent ground strips on the surface. See this: http://www.polarinstruments.com/support/cits/AP153.html
http://www.polarinstruments.com/support/cits/AP125.html

Craig Sullivan
Manufacturing Engineer
MPL Incorporated
P: 607.266.0480 x115
F: 607.266.0482
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-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Louis Hart
Sent: Wednesday, September 18, 2013 12:01 PM
To: [log in to unmask]
Subject: [TN] impedance measurements for coplanar waveguide

Technetters, how does one make impedance measurements on what I think is a grounded coplanar waveguide?

The configuration is, in one plane, what appears to be a signal trace flanked by two much larger conductors.

I have a Tektronix time domain reflectometer with P8018 (for single-ended impedance) and P80318 (for differential impedance) probes.

I called Tektronix, from which I have gotten excellent information in the past on other matters, but the technical support could not advise on this matter.

Thanks for any insight.

Louis Hart
Compunetics
Monroeville, PA
USA
[log in to unmask]<mailto:[log in to unmask]>
412-858-1232


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