when i simulated on cst i didnot need the complex but if you need the complex you can see on arg(S) parameter thus you can see the complex of s parameter...
like said suzanna you have magnitute of s parameter on linear scale and the argumant of s parameter.
complex s parameter = magnitute of s parameter *(cos (arg) + j*sin(arg)) you can use on all frequnecies one by one