Hello,
The first MOBILE AUX port looking from the left acts as a diversity antenna port, meaning it is used to achieve a stronger and cleaner signal when compared to only using the MAIN antenna. If only two antennas will be used with this device, the first AUX and MAIN ports should be used.
The two remaining SMA ports are purely for 4x4 MIMO support. If you’re not planning on using these ports, it is better to cap these ports with 50Ω RF terminators.
Hope this answers any questions!
Best regards,