You need to insert field monitors (far-field) at the frequency of interest.
After simulation is complete, you can view the results in the farfield section in the navigation tree on the left side of your window. You can then right click and select polar plot which enables you to select the plane of interest by varying theta (elevation angle) or phi(azimuth angle).
If you require further assistance, it would be easier if you could post screen shots of your 3d radiation pattern.