pmc ground plane

Hi,everyone

I am using HFSS to simulate dipole antenna near PMC ground plane. the dipole is parallel close to the PMC ground plane.

when i simulate this dipole antenna for 2.4Ghz centre frequence and place it very close to PMC ground plane 1mm to be exact i get good matched dipole shown by s parameter.

But when i check the farfield pattern at 2.4 Ghz,discovered the dipole antenna is parallel close to the PMC ground plane farfield pattern and dipole antenna is same in the vacuum farfield pattern.

In other words the dipole antenna is parallel close to the PMC ground plane,farfield pattern at 2.4GHz not any change.

If the dipole antenna is parallel close to the PMC ground plane,according to the image theory can produce with the dipole in-phase current in the PMC another end.

Therefore its far fieldfield pattern directivity and gain at 2.4GHz is not can increase
two times?

Some people can help me to explain this phenomenon?

Or the simulation method has the mistake?

Thanks.

kuanfu.