Gain problem of dual band microstrip patch antenna in HFSS-need a quick help

Hi everybody, ı am bs student and new at this forum.
I supposed to design dual band microstrip patch antenna for WLAN operations for my thesis. I used inset fed for my design. Antenna operates in 2.45 Ghz (between 2.40-2.52 ) and 5.80 GHz (between 5.70-5.88 ). I obtained good directivity and gain values for the 5.80 GHz band. However, in the 2.45 GHz band, ı obtained negative antenna gain despite the positive directivity. How can I fix this problem? Please help me...

This is caused by loss in the antenna: lossy dielectric material and conductor losses. On lossy substrates like FR4, the gain of patch antennas is pretty bad, and your simulation shows that if you include the dielectric losses (tand) in the simulation.

Thank you for your answer :) Yes, unfortunately, ı have to use FR4 substrate because it is only material that can we use in the laboratory to print the antenna. Is there any way to reduce the dielectric losses without changing the substrate material?

No, there is no easy solution.