Antenna interaction
I have a project where I put a GPS antenna (25 x 25 mm) and a 868MHz (fi = 10mm) small helix close to one another (16mm). They do not work simultaneously.
Can I expect some undesirable effects?
Thank you
Yes, you should expect some effect of either antenna on the other depending on how close they actually are. The presence of metals near radiating structures affects the radiation pattern and matching of the antenna. In your case, keeping a helix near a patch antenna affects the patch antenna even if the helix is not operating. You can try and simulate this in HFSS.
Anything on the pcb will impact antenna operation, especially radiation pattern. however, they are pretty far apart in frequency, so the loading is probably tolerable. Since the 2nd harmonic of the 868 MHz is close to GPS frequency, you really have to make sure that any transmitter is turned off (no broadband noise output) if you expect the GPS to work well.