I am making a prototype with a Raspberry Pi Compute Module CM4, which has an IPEX connector for an exernal 2.4/5GHz Wifi antenna. This is in a thick aluminium box which provides passive cooling, so I need to add an external antenna. I experimented with a flexible FPC antenna like this one
https://www.mouser.de/datasheet/2/418/8/ENG_DS_2108792_B1-2065479.pdf which is meant to be mounted on a plastic enclosure. However, when stuck onto a ground plane it didn't work as desired.
Is there any solution, apart from a traditional stick antenna? Or is there a way to get these FPC antennae to work on a metal box, for example with a suitable spacer? (Since the wavelength at 2.5 GHz is about 12cm and half that at 5GHz, I assume that it would need to be at least 1/4 wavelength away, so several cm minimum.)
I'd be grateful for any advice.
Cheers,
Bruce