bow tie antenna substrate and impedance design,need help

hi,can any one help me in designing bow tie?i am thinking of designing it for 100 ghz and i use formula for length l= lemba/2*sqrt(epsilon) and width =1.6*lembda/sqrt(epsilon) now my problem is that how to find out flare angle?i-e tan(theta)=l/2/w/2 is ok for full bow angle or it gives half of flare angle?
secondly on hfss when i define lumped port for feeding bow tie then what should i take impedance value?i-e 50ohm and rectance of 120 ohm is ok?i dont understand how to define resistance and reactance here.
thirdly substrate thickness?how can i select substrate thickness for bow tie is there any criteria for substrate thickness?
if some one can guide me it will be great favour.
also one more thing if i am designing this antenna for frequency 100 ghz then how can it work in wide band?