Your project looks really interesting. Some suggestions come to my mind:
- You can try changing the case material. Also you could try testing your project out of the case to discard if the case is causing issues in the connection.
- You can use an external antenna and connect it to the Edison’s antenna connector. Something like this: http://dlnmh9ip6v2uc.cloudfront.net/datasheets/Wireless/WiFi/ENG_DS_2118060_A.pdf. With an external antenna out of the case you would not have the connection issue caused by the case.
- In the same line of using an external antenna, you can use a U.FL to RP-SMA interface like this: https://www.google.com/search?q=interface+Cable+RP-SMA+to+UFL&es_sm=122&biw=1600&bih=815&source=lnms&tbm=isch&sa=X&ei=1Q…. With this way you can use RP-SMA external antennas like this one: https://www.google.com/search?q=interface+Cable+RP-SMA+to+UFL&es_sm=122&biw=1600&bih=815&source=lnms&tbm=isch&sa=X&ei=1Q….
For those suggestions you would not be using another Ceramic Antenna. Only the Edison's embedded antenna. Actually, I don't understand why you are using another ceramic antenna in your custom PCB if the Edison already has one.
A final thing, you mentioned the TI SWRA092B. You can check its datasheet here: http://www.ti.com/lit/an/swra092b/swra092b.pdf, I'm not sure if you already have it.
I hope you find this information helpful.
Thanks you very much for you answer.
I can confirm that the metal wall create perturbation because if I keep the bottom and the top only I have no problem. I also have a full plastic case (more small) and it works well.
Like you explained, I ordered the LSR external antenna "2.4 GHz FlexNotch Antenna" which is really small (I have small place).
Basically, for maintenance purpose I would like to have a really simple system: Edison, bottom PCB, top PCB and nothing else. I think it could be really hard but it's my target. For this reason I tought that introducing a ceramic antenna on the top PCB will be simple, take tiny place and could avoid perturbation like an external antenna will do.
I already saw the TI datasheet but I couldn't compare technicals information because I don't now what is required by the Edison module (power, db, etc.).