Hi, pennyslyn:
I am on travel and my notebook does not have software for the .rar file. You can send me the .zip file or I will answer your question after I am back to office. Regards.
Added after 59 minutes:
Hi, pennyslyn:
I am able to unzip your file now.
I checked your PIFA. Please display the vector current distribution on your structure. You should pay attention to the direction of the current.
There are current in both x and y-directions on the patch and the ground plane. There is also strong current on the probe and the shorting pin. It is good for omni-direction. However, you will see only the x-directed current on the patch and the ground is not kind of out of phase. The y-directed current is out of phase on the patch and on the ground. It causes a dip in the radiation at the theta = 90 and phi = 90 angle by the patch and the ground. For the probe and shorting pin, you can also see they are out of phase. The probe and shorting pin are at about the same x-location. They will create little radiation in the x-direction (theta = 90 and phi = 90). Then, x-directed current does not have any radiation in the x-direction.
For all the above reason, you see a dip at theta = 90 and phi = 90 or x-direction.
Regards.