Planar antenna radiation efficiency >1 in HFSS

[ifelix]

Hi,
I've done a model in HFSS for an inverted planar F antenna for 868 MHz on a FR4 substrate of 100x85 mm^2 and a ground plane 100x65 mm^2.
I've fed the antenna with a microstrip line designed for 50 Ohm impedance.
I've also used as radiation boundary a vacuum sphere of radius 270 mm, more than 3/4 lambda at 868 MHz.
I've assigned to the antenna and ground, copper finite conductivity to define a model as real as possible.
I've strongly seeded the mesh on the radiation boundary knowing the problems related to antenna parameters accuracy but however I've obtained radiation efficiency major than 1 all over the frequency sweep from 700MHz to 1.1 GHz.
Why?Could anyone help me?
Thanks in adv.

 

[savedadogs]

Please search the forum, this question has been asked many times... most likely due to inadequate meshing on the airbox boundary. Please take a look at this tutorial to make sure you setup everything correctly/optimally:

https://www.emtalk.com/tut_1.htm

and this

https://www.emtalk.com/forums/viewtopic.php?t=4

for information about the meshing.