Hello Miky,
Your EMSight Slotted Loop Antenna setup is wrong, based on the paper I have modified the following...
removed internal ports (+1,+2) & added Via Ports
Enlarged the Enclosre, & placed the structure to the middle of the enclosure box
Added additional Air Layer below substrate & set Boundary conditions as Open
Then added a explicit Ground layer metal below substrate
Then simulated it gave good results....
I tried the same with AWR new Axiem em simulator & it is matching....
The above modified MWO file is attached for your reference...
---manju---