FreeLists / si-list / [SI-LIST] Re: Measuring Characteristic Impedance of a PCB trace

["tao xu" <helen.tao.xu@xxxxxxxxx>]

Hi, Cody
my first thought is that you can make the trace short to avoide the
resonance appearing in your intrested frequency range. But please make sure
length is till much bigger than width.

thanks and regards
Helen


On 9/5/07, codymiller@xxxxxxxxxx <codymiller@xxxxxxxxxx> wrote:
>
> All,
>
> I am trying to measure the characteristic impedance of a strip line
> trace, using a VNA. I would like to determine the frequency at which the
> trace becomes very lossey. I am using a formula found in the Agilent
> Impedance Measurement Handbook page 5-23.
> http://cp.literature.agilent.com/litweb/pdf/5950-3000.pdf
>
> The method requires S11 of the transmission line open as well as S11
> with it shorted.
>
> |Zo| =3D sqrt(|Zopen|*|Zshort|)
>
> The method seems to work except I get some resonance at different
> frequencies where the impedance increases significantly. The frequencies
> of these resonants changes with different lengths of PCB trace.
>
> Can anyone recommend a different method for measuring characteristic
> impedance over frequency?
>
> Thanks,
> Cody Miller
> codymiller@xxxxxxxxxx
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