Urgent: how to simulate 50 ohms feedline in HFSS?

[KJolie]

I am relatively new to HFSS and need to simulate a 50 ohm feedline for a monopole slot antenna. The antenna is from the literature and it specifies a 50 ohm feedline, and I am not sure how that is simulated in HFSS. The feedline width and length is 2mmx16mm and the substrate thickness is 2mm with relative permittivity of 4.4. I have entered these paramaters in this characteristic impedance calculator at

http://chemandy.com/calculators/microstrip_transmission_line_calculator_IPC_2141.htm

but it's coming up with 70 ohms instead. So I am not sure where 50 ohms come from.

Also, I learned that transmission feedline length should be lambda/4, but how does that relate exactly to a feedline with characteristic impedance of 50 ohms.

If you would like to check out the antenna I am trying to simulate, it's at

http://ohd2007.esisar.inpg.fr/pdf/41.pdf

and it's the first one: Printed Rectangular-Slot Disc Monopole Antenna

I would really appreciate your straightforward reply to my query as I have researched the forum already and there is a hit and miss discussion around this topic.

Thank you.

P.S. This is really an urgent request.