Calculating SNR in HFSS

I want to calculate the SNR according to formula
Hx+jHy/R^(1/2) in HFSS. Does anybody help me doing this calculation. R is input impededance, and i also do not know how to measure input impedence.

hi
Mr.D sent me fields calculator cookbook and it may help about calculation. however I do not know how to find input impedance.