I know the basic design requirements for pcb trace antenna, no ground place below or above the traces, impedance matching etc. But the design layout recommendations for pcb antenna doesn't seems to answer my question.

My circuit is very small and I also have multiple PCB stacked one above the other (similar to the iphone X motherboard).

My question is what is the safe distance from the trace pcb antenna to other vertical grounds? i.e. imagine i have 3 pcb 1.6mm stacked one above the other with the top being the antenna. Can I have a GND place on the bottom pcb, between 3.2 and 4.8mm below the trace antenna?

Edit: Found this SMD antenna that they say that doesn't require GND clearance: 2.4 GHz SMD On-Ground Antenna

  • \$\begingroup\$ I think you have to consider this while designing the antenna. The ground plane will act to reflect the radiation from the antenna no matter where it is. \$\endgroup\$ – Hearth Mar 17 at 19:44
  • \$\begingroup\$ True. My question then is if I can get away with it moving a GND place very far from it (3.2 to 4.8mm). Just found this 3D antenna that does not require any ground clearance.. digikey.com/Site/Global/Layouts/… \$\endgroup\$ – Luis Carlos Mar 17 at 19:56
  • \$\begingroup\$ They deliberately had put it on the very edge of the board … \$\endgroup\$ – Janka Mar 17 at 20:03
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    \$\begingroup\$ What your are proposing is in the realm of "things best to avoid" but a definitive answer is not possible without either a) building it and evaluating it at least in use but formally in an expensive anechoic chamber with expensive test gear or b) doing modeling of a complexity you are likely unprepared for. How many are you building? How well does it need to work? What is the consequence of the first iteration being less than satisfactory? \$\endgroup\$ – Chris Stratton Mar 17 at 20:08
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    \$\begingroup\$ A PCB antenna designed to operate with no GND under it will not work. But that antenna you linked to could work. In general, when you put metal near an antenna (apart from whatever was anticipated at the design stage), it can change the input impedance, change the center frequency of the antenna, change the radiation pattern of the antenna. All of these can be bad. For typical bluetooth antennas, moving the center frequency can be pretty catastrophic. If you have the right tools, you may be able to tune the center frequency back where it is supposed to be with matching elements. \$\endgroup\$ – mkeith Mar 18 at 0:07

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