negative gain in patch antenna

i designed a circular polarize patch antenna of patc 80×80mm sq and substrate of size 90×90mm sq at 920MHz. the inner and outer radius of co axial port is 1mm and 3.9mm ,ε=3.38 but i got gain in negative.please tell me why my gain is in negative and how it will be positive.
Thanks

Hi

I guess you what a patch size there is approximately half a wavelength long on your substrate. I think what you have is to small, but try to calculate.
Also what is the size of your ground plane? is it the same size as the substrate? It needs to be at least quarter of a wavelength larger than your patch in all directions.

There can also be other causes within your simulation, that can cause issues....

Regards

What loss tangent have you simulated?
What is the simulated S11?