Re: [SI-LIST] : Controlled impedance in Flex Circuit

Shawn Carpenter (scarp@sonnetusa.com)
Thu, 26 Mar 1998 17:16:31 -0500

Frank:

When computing the wavelength of a particular transmission media,
you usually need to have the effective dielectric constant, which is
usually different (usually less) than the dielectric constant of the
board or substrate.

The wavelength can be computed by:

Wavelength in free space
Wavelength(media) = -----------------------------------
SQRT(effective dielectric constant)

You can get the free space wavelength as follows:

Frequency in Hertz
Wavelength in free space = ------------------
3.0E+08 (speed of light)

In Roland's case, the dielectric constant didn't change significantly
over
frequency, so the effective dielectric constant values were valid for
both
frequencies (give or take under a tenth). Other transmission line types
may
be more dispersive and this might not hold in other cases, so you might
have
to recompute it at different frequencies.

--Shawn

Chip Chip wrote:
>
> Shawn,
>
> Good analysis for Roland's question.
> Could you tell me how to get the wave length at 1 and 10GHz ?
>
> Thanks.
>
> /frank
> Chip & Chip Inc.
> frank@chip-chip.com

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||  Shawn Carpenter
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