Re: [SI-LIST] : Merits of low dielectric constant

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From: Fethi Bellamine (fethi.bellamine@alcatel.com)
Date: Tue Jun 27 2000 - 11:56:04 PDT


"Ingraham, Andrew" wrote:

> >Co (intrinsic capacitance) is directly proportional to Er
> >The correction factor for Zo for capacitive loading is proportional to
> >SQRT(Co) for small Co
> >
> >Therefore, the correction factor for Zo for capacitive loading becomes
> >proportional to SQRT(Er) for small Er.
> >
> >Therefore, the correction factor is smaller for smaller Er.
> >
> >Am I on the right track?
>
> I think this "correction factor" you speak of, is for a capacitive "stub"
> hanging off a main transmission line.
>
> If you are using an electrically short, unterminated coax, attached to the
> middle of a longer transmission line, then this is a consideration.
>
> If you are using terminated coax transmission lines and no unterminated
> stubs, then I think it's irrelevant.
>
> Andy
>
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The merits of low dielectric constant are lower propagation constant for the
undesirable waves, called
surface waves. The attenuation of these waves depend though on the height of
the substrate.

fethi bellamine
Alcatel CID

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