HFSS 13 Printed Dipole Antenna [URGENT]

Hi everyone,
I'm currently designing a printed dipole antenna at 433MHz using HFSS 13 and i have a few questions/ problems:
1) What is the actual use/effect of ground plane for a printed dipole antenna?
2)the toroidal radiation pattern is heavily distorted.
3)how to place the ground and the dipole radials effectively? should they be on the same side of the pcb?

thank you very much in advance.

Assuming substrate material in the range of 1...5 mm, don't put ground plane under the dipole. The current that is induced in the groundplane (by the dipole) cancels virtually all radiation. This results in very low input impedance (center fed case), narrow bandwidth and poor efficiency.

You mentioned dipole and dipole radials. This is confusing, please post your geometry to enable us to provide you better feedback.

Thank you, as per requested here is my design.

Can you post an image, as I don't have HFSS.

Sorry for the inconvenience. I've attached both designs. the first one contains its 'dipole radial' on both side of the PCB board with the ground at the bottom. On the second one, the entire design is on the top side of the pcb with the balun at the bottom side. thank you.

As far as I can see, both designs are half wave resonating structures parallel to the edge of the ground plane.

The dipole induces current into the groundplane (in Y direction), so your ground plane becomes an antenna also (and radiates in the XZ plane). The two fields interfere with each other and that causes the radiation pattern not to be omni-directional in the XZ plane.

You can see the current in the (edge) of the ground plane by looking to the current density plot. The current density is of course lower in the ground plane, but it extends over a relative large surface, hence giving serious interfering radiation.

Thank you very much for your help. So in order to solve this problem,do i need to redesign my printed dipole antenna with a smaller square shaped ground plane? Actually what is the exact purpose of having a ground plane at all(since a printed dipole antenna can function with out it)? Most of the pcb design in the net comes with the ground plane.