[SI-LIST] Re: S-parameter passivity... Interpreting the results.
- From: "Hill, John" <jhill@xxxxxxxxxx>
- To: "travis ellis" <travissellis@xxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Tue, 13 Jun 2006 16:39:15 -0400
Travis,
Try thinking small. Start with something you know like a 50 ohm
resistor. Measure it in your fixture. Are the results okay? If you are
near a high power transmitter or if there is a welder nearby you could
be receiving interference. Also look at the power level of the driving
port. Does the noise change with a change in power level?
The phase discriminator in the VNA needs a minimum signal to detect the
phase. If you have a big VSWR there may not be enough signal to detect
the phase. Check the specification on your VNA. The VNA has a receiver
in it. Is there something going on that could cause a problem to a
receiver? Is there a big out of band signal? Does it help to put pads
between the VNA and DUT? Remember to recalibrate with the pads in place.
BTW, what VMA are you using? Is there a DC block in the unit?
Best regards,
John
________________________________
From: travis ellis [mailto:travissellis@xxxxxxxxx]
Sent: Tuesday, June 13, 2006 12:19 PM
To: Hill, John; si-list@xxxxxxxxxxxxx
Subject: RE: [SI-LIST] S-parameter passivity... Interpreting the
results.
I'm using the 8052D broadband economy calibration kit. I've performed a
full 2port SOLT calibration calibrating out the cabling. All of which
use 3.5mm connectors. Then I attach port 2 to a 3.5mm - GPPO connector
that attaches to a 0.085 gppo terminated cable on one end. The other end
of the cable (DUT) has a coaxial probe. Port 1 is attached to an sma to
gpo connector that is mounted in a brass block and ground smooth. This
provides a coaxial structure that I make contact to with the coaxial
probe that is on the other end of the dut.
Travis
"Hill, John" <jhill@xxxxxxxxxx> wrote:
Travis,
Which Calibration kit are you using and can you describe what is between
the calibration plane and the thing you are trying to model? BTW, what
RF connector are you using?
Best regards,
John
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-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of travis ellis
Sent: Tuesday, June 13, 2006 11:00 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] S-parameter passivity... Interpreting the results.
I've been taking measurements with a VNA then running them through a
passivity checker. The basis for the code was originally posted by Ray.
I've modified it to meet my needs. Added plotting capabilities, log mag
format handling, and nudging of the non-passive values when only a few
points are out of spec etc. I don't think I broke anything in the
process but what I've noticed is that the eigen values of some of my
measurements are very noisy. The better measurements oscillate too but
they trend upward with increasing frequency. The suspect measurements
oscillate between near 0 and approximately 0.4 from point to point
across the higher frequency bands. The magnitude of the s-parameters
seem to be noisy as well. I've gone through my setup to make sure that
my cables don't have loose/bad connections. Replaced some connectors
that seemed inadequate and while things got marginally better the
measurements still contained noise. The noise source seems to be my
fixturing. Unfortunately I don't think I can improve this given my time
constraints.
The only thing that I've noticed is that the time domain simulations
take longer than those created with a data set that isn't as noisy.
Is there a way to decide if these models are accurate enough to be
reliable?
Regards,
Travis
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