MIFI LTE very slow

Routers
73

If you are sure that you are only using Band 7 (B7 FDD) then something like this will work:

https://www.amazon.com/VizGiz-B593S-850-Wireless-External-Connector/dp/B07C9RCFXD/

Just search for a 4G antenna that can handle 2600mhz.