# CPW Calculation - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues. Original posts:

ljoseph
Post subject: CPW Calculation Posted: Wed Sep 19, 2007 9:16 pm

Captain

Joined: Tue Sep 04, 2007 7:54 am
Posts: 13
Location: Dallas
Hello
With the following parameters, I am getting different answers with different tools.
H = 0.3mm
Er = 4.25
W = 0.56mm
T= 32.5um
gap = 0.35mm
Freq 1842 Mhz

With this Agilent Appcad gives 50.2 ohms. AWR Tx line gives 47 ohms.
Following online calculator gives 78 ohms.
http://www1.sphere.ne.jp/i-lab/ilab/tool/cpw_e.htm

Don't understand the reason for this difference.

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Jeanalmira
Post subject: Posted: Tue Sep 25, 2007 3:01 am

General

Joined: Tue Mar 15, 2005 11:43 pm
Posts: 65
Location: Singapore
Hi ljoseph,

the difference is the ground plane.
I believe that for your first calculation (AppCad and AWR) you included the groundplane (CPW ground)
While the online calculator is without ground plane.

you can double check the setting thru AppCad and also AWR (CPW and CPW ground).

Hope it helps.

Regards,
Jean

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imodelit_moderator
Post subject: Posted: Tue Oct 16, 2007 5:40 am

Captain

Joined: Wed Jun 20, 2007 3:01 am
Posts: 22
Dear ljoseph,

I'm with Jeanalmira in his opinion. As for the lower impedance values you used -most probably- Grounded-Coplanar. While the larger values is for the conventional coplanar waveguide -without lower ground plane-.

Kindly check this online applet, it is for conventional coplanar waveguide.
http://imodelit.com/ViewDetails.aspx?AID=190 Thanks.

Best Regards,
imodelit Moderator

Posted  11/12/2012

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