MAX BR1 Mini - what is the difference of cellular ports?

The MAX BR1 Mini comes with 2 cellular antenna ports - one marked CELLULAR MAIN and one marked CELLULAR DIVERSITY/AUX - do anyone know the difference?

Routers are mounted inside buildings, and we often need to extend cellular antennas, so they are placed in front of windows. When doing so, is it then necessary to extend both antennas or would it be sufficient to extend the main?

In brief, two cellular antennas are recommended to take advantage of diversity receive and will generally improve performance, sometimes very significantly. I’d recommend effective antennas be connected to both jacks. The Peplink “mobility” series may be a good place to start – two or more antennas contained within a single housing.