HFSS simulation for Wave ports of micrsotrip patch antenna( Results problem)

I have to verify the results of a differential microstrip patch antenna of a research journal for my college project. The antenna consists of dual patches which are electromagnetically coupled (Antenna design attached).

The simulated VSWR and gain plot are attached along with the simulated results of the paper. As you can see I am not getting the correct results.

Is it because I am using wrong wave port size ? Or something else is wrong with the design?

I have gone through many threads here and have applied changes but couldn't get the desired results.

I am very new to EM simulation and would be really grateful if someone can point out where am I going wrong.

Thanks

I forgot to add that the simulated results in the paper are using IE3D. Can we get very close results using HFSS and IE3D ?
And yes I added an extra ground plane to the top patch which is removed now. Still the results haven't improved much. Any suggestions would be very helpful