Wireless Joint

I have a MoFi4500-4GXeLTE-SIM7 hooked to two external Wilson Wide Band Directional Antennas. For over 15 months I was getting 30-40 mbps. About 3 weeks ago, the speed dropped to 6-8. I have tried a number of things with no luck and have come to the conclusion that Verizon/PagePlus has decreased my speed. I started to investigate aggregation but am finding that it is not possible on my router. Since I have two antennas connected but can't aggregate is there any advantage having a second antenna? Why would the manufacturer have two antenna inputs to the router? Thanks for your assistance.

For aggregation or improving SINR. The modem can use the signal from all antenna ports to improve the overall signal to interference plus noise ratio (SINR). My bet is if you disconnected the diversity antenna and watched your SINR levels you would find that it isn't as good as it was which ultimately reduces your upload/download speeds.