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How can I measure SMA devices with Agilent 85033E 3.5 mm cal kit?

Question asked by drkirkby on Apr 3, 2013
Latest reply on Jun 22, 2013 by drkirkby
I've got an HP 8720D VNA and Agilent 85033E calibration kit, and want to measure an SMA female device. That device is actually an SMA short and I want to find the distance between the reference plane and the short. But the results I'm getting don't look too good, and I suspect its due to the mis-match between SMA and 3.5 mm, but I may be wrong.  

But I don't know how best to correct this, or at least reduce its effects. 

If I take the *3.5 mm female short standard* from the 85033E calibration kit, and apply a port extension equal to the offset delay of the short, then on the Smith Chart the device looks like a dot on the left. No great surprise that 

If I now replace the 3.5 mm short with an *SMA female short*, I am unable to find any port extension at which the Smith Chart shows a dot on the left. The Smith Chart view (hand edited as my software was not displaying it very clearly), shows the view with a port extension of 25.854 ps. Note the phase first goes in one direction then changes direction around 3.5 GHz. It should be easier to see on the graphs plotted with Excel.

Any thoughts on what I can do to find the offset delay of this SMA female short? 

I've attached two Touchstone files. 

* sma-short-0ps.s2p is the SMA short measured with *no port extensions*. 
* sma-short-25.854ps is the SMA short measured with *25.854 ps port extensions*

Has anyone any comments as to whether my results are surprising, or what (if anything) can be done to improve matters. 

Perhaps I am just asking too much of a non-precision connector. 

Dave

Edited by: drkirkby on Apr 3, 2013 8:12 PM  

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