WiFi WLAN antenna for metal enclosure, short with IPEX connector

[ballen]

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

[nali]

Ceramic patch antennas are designed to work on a groundplane. You can try searching for "puck" antennas if you want a finished product - not sure if you'll get one with an Ipex connector though, they normally come with SMA or SMA-RP so you'd need a pigtail unless you replace the cable (some are screwed together so you can do this easy enough)

[ballen]

Thank you very much, I did not know about these.  From looking at some of the datasheets, it appears that they are intended for thin copper groundplanes like PCBs.  In my case I have an aluminium enclosure 4-5mm thick.  Do you know if they will work close to the outside of that?

[nali]

Well what can I say... I have a couple of these
https://aampantennas.com/product/wifi-zigbee-body-mount-antenna/

and lookee what's inside: (attachments)

If you get a body mount antenna and can't get inside it shouldn't be too difficult to snip off the coax leaving a small stub, put a SMA connector on it and use a small SMA-IPX adaptor like this -