calculate parameter need for design cavity comb line filter

[maryam]

i design combline filter whit equations for tapped round rod combline filter such as follow:
Si,i+1 = b (0.91d/b + 0.1529 – log  ( 2 / Sin 2 + 1) KComb i,i+1  for i = 1 to n-1
1.37  f0  (17)


C(pF) = 159.16 where f0 is in GHz (26)
tan f0 Zi
min end gap (mm) = 0.695D2 where D is the resonator diameter in mm. (27)
100C - 2.61 D & C is the required capacitance in pF

but filter simulation in hfss11 dosnt filter response,idont know what is uncorrect in my design ,:?:
please help me.