port voltage and current in CST

I use CST MW to simulate an antenna, the port is a discrete port (for s-parameter caculation), and the box "monitor voltage and current" is selected. So I got the voltage and current information of the port in different forms(time domain, frequency domain) at the folder "1D Results/Discrete Ports/Voltages" after simulation.
The problem I'm stranging for is that: the frequency response(abs(U) linear) is not the frequency domain of the given port voltage(Signals) given in the same folder, but the frequency domain of the reflected wave(at "1D Results/Port Signals/o1,1").
Hope for help and discussion.
If anyone has questions, pls let me know.
Thank you all for your attention in advance.

Anyone help?

Disrete port is not suitable for S-parameters. Rather i suggest you to define waveguide port.

Is it? Can you explain it in more details? And the question is still exist that waveguide port can not be used in some cases, for example, dipoles. Thks!