Deducing Feed line length and port impedance

I'm trying to replicate a microstrip antenna in one of the papers using HFSS. All dimensions are shown except the length of the main feed line. The paper shows the resulting Z and S11 curves but it does not say the length of the feedline. I'm assuming the port will have a 50 ohm impedance. However I don't know what the exact length of the feedline is. I'm getting close Z and S11 curves but changing the feed line length changes both curves (the location of the resonances and the values of Z and S11 depend on the feed line length). Any idea how to deduce this length?

Hi
What type of port you/paper have used? You may use "deembed" option in post processing setting of the port.