Omnidirectional Antenna Optimization in HFSS

How to set up the Goal in optimization setup in HFSS in this case: the antenna is on xy plane, i want to find the value of a variable so that the antenna is Omnidirectional in yz plane
I don't know how to set up the goal, the condition.. in optimization setup menu
Thank you very much!

Hi

I would say minimize the difference between the MAX and the MIN of the gain in this plane.

Thanks
Shehata

Hi Shehata,
thank you for your considering. There is one thing in your answer that i couldn't understand, please explain it for me!
You could look at the picture that i attached
i set up the calculation is: "max(dB(RealizedGainTotal))-min(dB(RealizedGainTotal))", the plane here is zy so phi=90deg, theta= 0deg up to 180deg, condition is Minimize.
So that the HFSS said " calculation ranges is not allowed when minimize condition is selected"
How could i solve it, please help me
Thank you very much!

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this is the picture of HFSS message
http://s1311.photobucket.com/user/AH...64b93.png.html

I have found the answer, thank you very much :)