Electronics > RF, Microwave, Ham Radio

Antenna placement 868MHz

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fantasy2:
Probably a very simple questions for all the experts here.

I'm very restricted in the available space to place an antenna for 868MHZ ISM range.
Below some pictures of the possible orientations. Option 1 would be the best, but then the antenna would stick out of the housing, which doesn't look nice and is more challenging to make it water proof.

Everything will be placed in an ABS housing.
Black = PCB contour with ground plane
Blue square = RF module
Blue rectangle = AA battery on other side of the PCB

What would be the least worse situation?
Option 4 is a helical antenna but the gap between a metal pin of the AA cell holder is 1mm max.





Another option would be to place the helical antenna behind the PCB like below. Is this realistic?

IkariShinji:
Not an expert. Here is my 2 cents.

By the look of your helical antenna, it is in normal mode, so it is not very much different from a monopole.

IIRC, if you put a monopole very close to the ground plane in parallel, the radiation efficiency will drop a lot.

I will go with either #2 or #4.

The easiest way is always to just mount it and measure the output power. Please update the results if you could.

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