dont exactly know, but the pod makes interferance with the shields, so that there is one second where the shields have to be remoduled..
In that time it is possible to beam 1 person through.
And I dont think that a simple pod that doesnt do anything else than scanning causes such an interferance.
And the design seems to be built on the AWACS airplanes, and their pod actually rotates, but dont know if its really canon..