help in waveguide simulation ,renormalizing (HFSS v 11)

hi all ... i need some help in understanding the use of renormalizing
i am comparing two simulations of rectangular waveguide exited by waveports. in one simulation have ended the waveguide in a radiation boundary condition ( to simulate semi infinite waveguide ) and the other simulation i have ended it with other wave port , and scaled the incident power to 0 so that the waveports acts only to absorb the radiations of the first port . Are these ways of terminating the other end of the waveguide to simulate a semi infinite waveguide correct?( i am getting different s parameters for both the simulations,why?)
if i want to compare the s parameters of both the structures can i do it directly or do i need to normalize them to a common impedance say 50 ohm?
Also what impedance does one uses to normalise the s matrix , port Zo or the Z11?
can any one explain me the difference between two?
I know i have too many questions in one post , but would be grateful to any one who can help me out.
Thanx in advance
Rohit bahl

hi.... can the experts of HFSS kindly help me ?
thanx
Rohit bahl