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How use 4- port as 2-port to extract S-parameter correctly

Question asked by mohammad1989 on Aug 19, 2015
Latest reply on Aug 19, 2015 by volker_muehlhaus

I want to simulation micro transformer in ADS (2011  and 2015).

I am confused about set Ports.

I have 4-Port transformer and . I want extract S-parameter.
i should convert 4 port to 2-port  (  port (1,2) in primary coil and port(3,4) in secondary coil  ) .and i think i have 3 way to do it.

1-use differential port( like  group (1,2) as one port ).

2-ground port 2 and 4 (cover ground under substrate)

3- use for port (as manual) and in plot display windows by multiport equation convert 4-port to 2-port (like define SD11 as new S11 and it is equal SD11=0.5*(S11-S13-S31+S33) )

i simulate all of them and i have different result.

which one is more correct and more common in papers?

I know that in fabrication port 2 and 4 will be grounded but i don't know how to ground that port correctly.