How to use CST to simulate the capability of electromagnetic wave mitigation

Hi, everyone

I?m just a beginner and studying CST from last couple of days. I want to simulate the absorber?s capability of electromagnetic wave mitigation. The electromagnetic wave, the frequency of which is about 6 GHz,is normal to the planar interface. I want to get the magnitude of EM reflection coefficient. But I don?t have any tutorial. Could you provide some corresponding tutorial? Or any suggestions?

Thanks in advance.