s-parameter of hybrid coupler

what is the physical significance of the s11,s21,s31,s41 curves in hybrid coupler?

---------- Post added at 16:22 ---------- Previous post was at 16:18 ----------

is that return loss,isolation.....

Hi shrestharekha,

S11 = return loss
S21 = through port
S31 = coupled port
S41 = isolation port

These parameter can have different meaning depending on how you define port 1,2,3, and 4. Generally, people stick to this convention.

Hope this helps,

Microwave123