On 6/24/2016 8:08 AM, jimlux wrote:
Or they use multiport VNAs and get to the result by algebra. If you
look at the measured test data for a minicircuits RF transformer, you'll
see full 4 or 5 port data.
http://www.minicircuits.com/MCLStore/Agreement.jsp?file=ADT1-6T_S5P.zip
I used to design network analyzers for Agilent (now Keysight).
A 4 port VNA is the gold standard for dealing with any sort of
balanced system. I had the use of an E5071C 4 port at work
and was able to make very definitive measurements of CAT5
twisted pair with it.
A 4 port VNA actually consists of:
1. A 2 port VNA with one source and one or two receivers.
2. A switch matrix to connect two of the VNA ports
to various combinations of two of the four DUT ports
3. A bunch of math to calculate common mode, differential,
and mixed S-parameters. Also, a calibration routine.
It does NOT use any baluns whatsoever. It never generates
pure balanced or pure common mode drive signals nor does
it have the corresponding receivers.
It is therefore possible to fake a 4 port VNA using only
a 2 port VNA if you do the various interconnections manually
and have a math routine to crunch the data. However, the
2 port VNA needs to be a true 2 port VNA. Many so-called
2 port VNA's should probably be called 1.5 port VNA's because
they don't have full 2 port calibration.
This is way beyond the capability of virtually all hams because
of the cost of the 4 port VNA (5 figures) and the complexity
of understanding how to use it. Let alone faking it
with a 2 port VNA.
Rick N6RK
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