RE: [SI-LIST] : Coplanar Transmission Line

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From: Jian Zheng (jian@zeland.com)
Date: Fri Feb 04 2000 - 08:40:07 PST


Hi, Chris:

Yes, I know CPW can have a ground plane. Some people will not call them CPW.
Instead, they will call the CPW with ground as CPWG. They have quite simular
features. For example, their parameters do not change much with frequency.
It is more due to the fact that the electric field lines are more parallel
to the substrate interface. The continuous tangential E-field makes the
field in both the air and the substrate about equal. When the field in both
the air and the substrate is about equal, we will get the effective
dielectric constant Ereff = ( 1 + Er ) / 2 , where Er is the dielectric
constant of the substrate. The ground plane will change it slightly.
However, it will affect this property much.

  | vertical direction.

----> tangential direction

          air
=====----------======---------========
          substrate
----------------------------------------------------------
Thanks!

----------------------------------------------------------------------------
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Jian-X. Zheng, Ph.D
Zeland Software, Inc., 39676 Mission Blvd., Fremont, CA 94539, U.S.A.
Tel: 510-797-8109, Fax: 510-797-8241, Web: http://www.zeland.com
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-----Original Message-----
From: owner-si-list@silab.eng.sun.com
[mailto:owner-si-list@silab.eng.sun.com]On Behalf Of Chris Padilla
Sent: Thursday, February 03, 2000 6:27 PM
To: si-list@silab.eng.sun.com
Subject: Re: [SI-LIST] : Coplanar Transmission Line

    A CPW may be composed with or without a ground plane--you'd better know
    which so you use the proper model/formulas. They are often built on
    structures meant for microstrips (hence the ground plane) since some
    designs mix the two TR lines. So a CPW could have 2 or 3 metal
    references.

    ----->Chris

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