Radiation pattern of 4 patch array antenna

[mianjuyan]

Hi, everyone:

I am simulating a 4 patch array antenna. I set the GND as an infinite ground plane. But the problem is that there is still radiation pattern under the ground. What causes this result? can someone tell me? Thank you very much!

Best regards!

 

[WimRFP]

What package are you using? How much dB is it down (the radiation below ground plane)?

Check the thickness of the ground plane and the conductivity. When you modeled the plane as a thin conductor with low conductivity, radiation will go through it.

You are sure you didn't make a slot in it (without knowing it)?

 

[mianjuyan]

Dear WimRFP

Thanks for your reply, it helps me think. The radiation below the ground plane is from -50dB to -80dB, it is quite small. The ground plane has no thickness, I just draw a rectangle as the ground plane.
I tried the similar simulation with single patch. When I draw a circle at the bottom of the ground plane and set it as a lumped port, there is radiation pattern below the ground plane. However, when I used the wave port, there is no radiation pattern below the ground plane. So is it because the lumped port? Could you explain this to me? I am not very clear about this. Thank you in advance.

Best regards!

 

[WimRFP]

You wrote that you just draw a rectangle as ground plane. Are you sure it is infinite as I would expect that you don't draw a ground plane when having an infinite one?

-50..-80 dB is very low (and hardly measurable on a real antenna), though it is strange that changing the feed causes radiation below the ground plane (if it is infinite). I would recommend you to mention what simulator you are using, maybe other people can comment on the feed issue.

 

[mianjuyan]

Dear WimRFP

Thank you so much!
I simulate with HFSS 15. I set the ground plane as "Perfect E", and I also select the selection "Infinite Ground Plane", so I think it should be an infinite ground plane.
I have some new results. When I draw a rectangle at the boundary of the substrate and set it as a lumped port, there is radiation below the ground plane (the patch is feeded by transmission line). But when I move the port a small distance into the substrate, the radiation below the substrate disappears. Why this happens? Do you know the answer?