definition of input impedance for a two-port in CST MWS

Dear all,
I am facing the problem of evaluating the INPUT IMPEDANCE of a slot inserted into a circular waveguide, which, as you know, it is different from Z11. The guide is terminated in one side with a wave port. At the end I have a two-port dev. As I used to do in HFSS, I wanted to define an output function:
Zin=(1+S11)/(1-S11)*Z0 where S11 is complex. Then i get the real and imaginary part.
In CST there's no way to get S11 complex. One can get amplitude and phase but as I define a post-processing template function, like:
Zin=(1+mag(S11)*exp(i*ang(S11))/(1-mag(S11)*exp(i*ang(S11))*Z0
And my idea was to take from it "im" and "re" parts. I try to define i=Sqr(-1) but gives strange results...
the program cannot recognize the symbol "i" (also "j") for the imaginary part. Does anybody know how to modify this expression the way it works? With HFSS is so easy...
viele Grü?e,
I.

Hi Ivan,
this is math functions inside CST:
Pi = 3.141592654...
re(am,phD) / im(am,phD) = Real or imaginary part of a complex number (am = amplitude, phD = phase in degrees)

SinD(x), CosD(x), TanD(x) = Sin, cos, tan with x being the angle in degrees

ASinD(), ACosD(), ATnD() = Arc sin / Arc cos / Arc tan with the result being an angle in degrees

ATn2(y,x) = Polar angle of the complex number x + iy measured in radian

ATn2D(y,x) = Polar angle of the complex number x + iy measured in degrees

Evaluate(x) = Evaluates the mathematical expression x and returns its numerical value (as double)