I am using a standard RF module (i.e., Bluetooth-module-on-PCB), which has a PCB-trace-type anntena. It is in turn to be soldered onto my main PCB. The whole thing will be powered by a standard Li-ion battery.

Which of the following two placements of the RF module would perform better, in terms of offering optimal transmission/reception?

(I prefer Placement B for logistical reasons but I am unsure about the effect of the RF module antenna's proximity to the battery, which I'm guessing will act as a huge ground plane.)

Placement A:

RF module placed on top of my main PCB (which I'll make sure to keep out the copper pour/traces, etc. in the area directly under the RF module's antenna) enter image description here

Placement B:

RF module turned upside down and placed between PCB and battery. enter image description here

  • \$\begingroup\$ Placement A is better. The copper of the main PCB will disturb the radiation pattern and change it. When the PCB is below, there are 180 degrees that basically have just air and this will help the propagation. \$\endgroup\$ – Gustavo Litovsky Oct 17 '13 at 14:41
  • \$\begingroup\$ @GustavoLitovsky: But will this be an issue given that, as mentioned, I have ensured the main PCB has no copper in the neighborhood directly under the antenna? \$\endgroup\$ – boardbite Oct 17 '13 at 15:08
  • 1
    \$\begingroup\$ Yes. Because that copper is still there. You probably have a clearance of a few milimeters around it. Even this is a compromise. You could always use a module without an integrated antenna and use a little U.FL connector with cable to place antenna outside of the sandwich. \$\endgroup\$ – Gustavo Litovsky Oct 17 '13 at 15:31

The main rule for such antennas is not to have any metal part near them, be it the board copper or not. Or, if this is impossible, to have them as far as possible. If you look at the area of the module around the antenna, you'll probably see that there is no copper in any of its layers. Given that, and provided that you made a keepout area on all layers of your board under the antenna, the two choices that you presented are almost the same, with the one in which the module is up marginally better because it's a bit farther from the battery. But even then the result may have quite low performance, because you still have lots of metal areas near the antenna. No matter what is the chemistry of the battery, it'll most certainly be totally opaque to RF, so the better would be to "slide" the module to the left until the antenna is outside the board area and there's nothing below it.

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You need to read the datasheet specification of your module.

I use one module that the datasheet tell to put the area of antenna outside of the pcb, and ground in other areas of the module.

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