Positif return loss with passif structure

Hello,

I have a problem with the antenna patch I am trying to simulate. I'm not able to add pictures so I am going to describe it.
- It's a metal patch on a substrate and back reflector with the same metal
- i added the phyisical properties of my materials
- I put a floquet port with lattice pair boundaries and i launched the simulation

In my dB graph:
I have a negative pic arround 35THz corresponding to my substrate (that's good).
But, i have a positive pic around 110 THz that should correspond to the patch.
I should note that when i use gold from the system i have about the same pic but negative, but i don't think
I declared my metal in a bad way as I just followed the documentation.

I tried some things to fix that but nothing seems to be working.

Thanks for your help (Im using HFSS)

Uploading images should go smoothly if you reduce file size under 200 Kbytes and make format png.

THz must mean teraHertz? We've heard of GHz and that's difficult enough to achieve.