coupled microstrip lines measurements

I have built a coupled microstrip circuit which is measured with the 4-ports single ended technique. I am trying to obtain 3 parameters: insertion losses for common and differential modes, and reflection loss for differential mode. So far, I have good results with insertion losses, but reflection loss is quite wrong. I cannot understand how this is possible if the three results are related with the individual S parameters of the whole 4-ports network.

If anyone have any idea I wll appreciate it.

That's an interesting measurement what you are doing.
Are you using the procedure described in Pozar's Microwave Engineering book ?

Actually I am taking the Mixed S matrix given by:

Vaz K. and Caggiano M., "Measurement technique for the extraction of differential s-parameters for single -ended s-parameters", Electronics Technology: Meeting the Challenges of Electronics Technology Progress, 2004. 27th International Spring Seminar

They are very intuitive and straigthforward. My problem is specifically with differential reflection loss. I have found that the phase of the insertion loss between the two individual entrance ports is forwared respect with the reflection of each ports (hopefully the last comment can be understood )