For optimal performance with the XBee Cellular module, the antennas should be placed perpendicular to each other and not touching.
For parallel placement, Digi recommends to have the antennas at least 3" (8cm) apart from each other. We also recommend that the antennas be placed perpendicular to any metal objects. If you are not able to keep the antennas perpendicular to the metal, then they should be at least 3" (8cm) away.
With all good practices with antennas, they should be kept away for all electrical noise sources that could cause interference or effect performance. If that is not possible, then the noise source that can cause interference should be shielded.
Jan 08, 2018