Hi,

I have recently simulated a WR-90 wave-guide in CST Studio Suite , with a length of 40 mm(I put two ports at input and output of the wave-guide). During my analysis, I examined the input impedance at the input port using post-processing on the S-parameters. 

I observed that the input impedance is given as Zin=1063−16046j at a frequency of 9.9795 GHz. Could you please help me understand how this particular input impedance value can be achieved for the wave-guide? 

Thank you.