The EE LTE Router Antennas have 2 Coax Feeders because there are 2 antennas inside the Housing, reason for this is for 2x2 Mimo.
Without getting too techy 2x2 Mimo will pick up and transmit two Signals on the same frequency from the Cell Site, although it's the same frequency the 2 Signals differ in there Data Transmission content as they are Transmitted out of Phase from each other, the benefits means Data Speed will almost double in this case whilst only using one Frequency Channel or Band so it's also Spectrum Effective.
Most LTE Routers now use 4x4 Mimo Internal Antennas within the Router itself, so you are effectively degrading the Routers Spec when using a 2x2 External Mimo Antenna in using one but it's a good compromise for Signal Strength increase in poor Signal Areas.
4 and 5G Networks currently use 4x4 Mimo, as 5G develops to the next stage it will use more than 4x4 or commonly known as Multi Mimo.
