This KBA provides some hardware tips about how to maximize the isolation between multiple antennas mounted on the same PCB. 

- Maximize the distance(s) between the antennas on the PCB in order to minimize the radiated coupling effects. 
- Place the antennas in opposite orientation, i.e. opposite polarization in order to maximize the isolation.

- The radiation patterns of antennas can also be taken into account during placement, i.e. try to place one antenna in the null point (or less radiating) direction of the other one. 
- Place the antennas on different layers, i.e. put one antenna on the top and the other on the bottom layer of the carrier PCB.

- Select antenna types which have a bit more concentrated and localized RF currents close to the antenna input ports. E.g. inverted F-antenna (over a simple monopole antenna). 

- If each antenna is placed at the PCB edge, then GND slot(s) - one slot between two antennas - on the common GND plane can be ensured between the antennas in order to minimize the mutual current and thus decrease the coupling effects. 

The shape and dimensions of these board-edge current-blocker slots can be the followings:
1. Simple straight slot with 3mm width and quater-wavelength length on the given PCB.
2. For a wider band approach, slot line radial stubs or even diamond-shaped slots can also be utilized - as shown in the design of 4455-LED-868 RF Stick, for instance (see the diamond-shaped slot in the printed balun area): 
https://www.silabs.com/documents/public/schematic-files/4455-LED-868.zip