In today's increasingly connected world, installations with multiple RF signal antennas are becoming unavoidable. Many application engineers will look at antenna placement and "hope for the best," when in reality the math involved in determining optimal spacing is not very difficult and should be carefully considered in the design before drilling holes and placing multiple antennas.
For 2.4 GHz applications where both 2.4GHz wifi and 2.4GHz cellular signals must be used, the antennae should be no less than 4.92 inches apart. It should be noted when using Technologic Systems enclosures, while pre-drilled for multiple antenna mounting locations, the enclosure itself is not large enough to provide appropriate spacing for multiple simultaneous networks operating on the same frequency. In applications that require both 2.4GHz radios to be operating simultaneously, antenna extension cables must be used to ensure proper antenna distancing.
There is an excellent article written by Southwest Antennas on the topic of antenna spacing found here: