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

[<codymiller@xxxxxxxxxx>]

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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