Insertion loss plot not starting from zero in HFSS

I imported my brd file in to HFSS through Allegro and ansoft links. I did all the necessary changes and analyzed. Now I am getting more losses compared to the measured data. At 10GHz I am getting -8Db loss.

One of my problems in that plot is the insertion loss plot versus frequency is not starting from Zero at zero frequency.

Anyone know why it is not starting from zero?


Thank You
Mani