Reg. EXCITATIONS in HFSS

hello all,
Whats teh use of "voltage" in "Assign excitation" in HFSS. i.e. if you want to assign waveport you select the object go to assign excitations and select wave port. now when do we need to select voltage etc...(apart from wave port there are other things in the list )
thanx in advance

Hi
I know - the excitation is voltage (or current) source between two points

hi,
thanx a lot . i'll explore it further