S parameter - Is it so hard ?

Hi,

I need help. A have transition from rectangular to circular waveguide. So return loss = X dB. Can you tell me, how is design S matrix ?
X in dB is 20log10(S11), so S11 = 10^(X/20) and S matrix is

[ S11 √1-S112 ]
[ √1-S112 S11 ] is it true ?

Thank

So it is so hard ? :) Or it is so easy ? :) A do not understand me ? Can you help me ? Thank

Can you tell me somebody, why nobody can give me answer ? :) Thank

Refer Collin's book.
Foundation of microwave engineering
He has explained how to write it.

Check Pozer too. i guess he has also given.
but not sure.