I am trying to extract the s-parameters for different structures. I am trying to get (S11,S12,S13,…,Snn); where n is the number of the ports in my structure as illustrated

I tried to follow the exact instructions illustrated in this example and apply it on a directional coupler (DC) that is symmetric about x and y axes.

I have done a FDTD simulations of that structure and the results can be found in DC.fsp (1.8 MB)

After finishing the s-parameters sweep, I extracting the s-parameter file DC_sparamaters.txt (571.9 KB)

an error message appears telling me that the device is not reciprocal

**Why this message appears to me?**

When I tried to visualize the s-parameters matrix. The DC is designed to be 50/50 at 1.55um and when I viewed the s-matrix at that wavelength it doesn’t show me a symmetry as expected (i.e. S14 doesn’t equal to S14 or S23 or S32)

**Why is not the s-matrix symmetric as expected?**

After importing the extracted file of s-parameters sweep in FDTD into INTERCONNECTS and doing the following setup

Then I run the simulation and viewed the transmission at each port to get the following result that doesn’t support the FDTD results. The transmission of both input 2 and input 3 should intersect at 1.55um, but it gives me the following response. DC.icp (729.8 KB)

**Why don’t the results from INTERCONNECTS follow the results from FDTD?**