why axial ratio changes?

in simulation, when we suspend the patch over ground plane, axial ratio changes. i need explanation why this happens physically.. thx. Also some way to handle this problem ll be well.

It may be affected by the size of the ground plane. Try your simulation with a ground plane many times larger than the patch.

no with a patch it should be fine with an infinite ground plane, how are you feeding it are do you have two feeds up through the patch or are they offset feeds? is it RHCP or LHCP? is it two patches or one patch fed with a 90 degree offset?

let me know,
Zach

Axial ratio is a function of amplitude balance between the components as well as the phase balance. Disturbing either will effect the axial ratio.

I agree that it is and that is why your axial ratio should change consistantly when making the ground plane larger (by the same amount on all sides) should not change your AR with a single patch fed the same now if you have two antennas it might change depending on your setup if you do not have the same ground connecting them and then you do, yes it will change.

my design is a circular patch antenna with one coax feed. with CP about 4 db. without elevation over ground plane. When i elevate( seperate ground plane below patch(with dielectric) 20mm,25mm,30mm etc.) i see that AR changing(in simulation).