Convert 2-port S-parameter to 4-port S-parameter in couple interconnet

Hello,
Coupled line with measure ports is shown below:(the "==" means the line,P1 and P4 is the measure prots)

P1 ==============P2
P3============== P4
The P2 and P3 is open.
How to convert this two port s-parameter into 4ports s-parameter?
Thanks ~~

I have the same situation, but unfortunately, there is no answer.

I am unable to understand your problem. How can you convert a two port result to 4 port without knowing the outputs at that port?

The situation is as follows:

Given the coupled lines, considered as a 4-port:

P1 ==============P2
P3============== P4

If P2 and P3 are terminated in Open, and VNA measurements are performed between P1 and P4, what is the relation between the initial 4-port S-matrix (describing the 4-port) and the measured 2-port S-matrix (obtained from VNA)

Interesting question here. firstly we should consider that the 4-port s-parameters for the device probably assume proper 50 ohm terminations at all ports. so I don't see how you can compare them. The coupler won't work properly without the right terminations.

mkonca is right S-Parameters are measured assuming termination on all other ports. See the theory of S-parameter. I am afraid you are on wrong direction.