# RE: [SI-LIST] : Coplanar Transmission Line

From: Jian Zheng ([email protected])
Date: Fri Feb 04 2000 - 08:29:59 PST

Hi, Sam:

Following are my COMMENT on your message.

> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]]On Behalf Of [email protected]
> Sent: Thursday, February 03, 2000 6:25 PM
> To: [email protected]
> Subject: RE: [SI-LIST] : Coplanar Transmission Line
>
>
> Hi Ron,
>
> Let me see if I can help.
>
> The electric field in a dielectric material doesn't change its
> polarity that
> easily as it does in air. Dielectric materials require some additional
> energy to change the field polarity that are associated with alternating
> currents. Such energy is derived from the travelling wavefront and
> dissipated as heat (resistive loss) inside the dielectric
> material. Thus, it
> is obvious that such energy loss keeps increasing with increasing
> frequency
> of the signal.
>
> Dielectric resistive loss is usually specified by the "loss tangent" for
> that material and is a function of the dielectric constant "sigma".

COMMENT: I agree with what you said. Loss tangent is equivalent with the
conductivity sigma. Normally, in a narrow bandwidth, the loss tangent is
constant. However, sigma is more a constant over a wide frequency. The
relationship betwen loss tangent and sigma is:

Ert = Er * ( 1 - j LossTangent ) = Er - j Er * LossTangent = Er - j Sigma /
( Omega * E0 )

or

LossTangent = Sigma / ( Omega * E0 * Er )

where Omega = 2 * PI * frequency, E0 = 8.86e-12

>
> Hope the RF gurus agree with me.
>
> Best Regards,
> Sam KVK
> AMD, Singapore
>
----------------------------------------------------------------------------
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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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>

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