Impédance of Patch Antenna

Hi,
I'm currently simulate a patch antenna at 800MHz with a coaxial feed above a substrate (Epoxy 4.3, h=1.6mm).
So, I'm interested by the variation of impedance along a patch.
Genearally, the impedance is zero at the center and ≈100-300Ω at the edge.

While, for my case, I find zero in the center , but in the edge I have only 60Ω!.

It's normal?.
Thanks

Hello,

Try to reduce the loss tangent of the FR4 material, this should increase the resistance at resonance. 800 MHz (375mm = lambda) and 1.6mm between patch and ground will not give you a good antenna, unless you have another patch above it.

If there would be no loss, the impedance should be in the many kOhm range. the reason for that is that the image in the ground cancels most of the field, hence resulting in low total radiated power given certain current in the middle of the patch.

If you want some useful simulation results (that is reasonable radiation efficiency), you should increase the distance between patch and ground, and if possible create a layer of air also. Of course this will result in a larger patch, but you will get an antenna that has reasonable efficiency.