Regarding PCB IFA microstrip antenna mirror image on ground plane hole areas

Question

This is regarding the adjacent mirror image formed over the ground plane by a PCB antenna during operation. Take the first image of the IFA with the ground plane highlighted in yellow on layer 2, the top signal layer is hidden in the image. Say I have some through-hole components or vias to other layers which would punch holes in the second layer ground plane as shown.

Now take the second photo of the antenna image mirrored over the ground plane as it would be during operation. Do these holes in the ground plane where the mirror image is forming have any effect on the function or effectiveness of the antenna, or degrade the performance at all?

Answer 1

Thanks for asking an intriguing question. The short answer is "no", you do not need to consider a mirror image of that inverted-F antenna when considering the adequacy of your ground plane.

The inverted-F antenna acts as a short monopole, and as such, you definitely need a ground plane. But without doing a full simulation, you can think of the RF currents induced in the ground plane as a simple set of radial spokes spreading out from the feed point. Your rows of four through-holes would be most troublesome if they were cutting across those radial lines, and least troublesome if they aligned with the radial lines. It could help a tiny bit to nudge them apart, so the ground plane isn't completely interrupted by the row of 4. If your PCB extends at least a quarter-wavelength in all directions, I'd consider it to be quite adequate.