If you know your nearest 4G relay then I guess something like this https://www.amazon.com/dp/B00RJQ8RGC/ref=cm_sw_r_cp_awdb_imm_M0PW41VH6AHZB6R1763A
This is a Yagi antenna that you should point to the antenna of the nearest relay.
You’ll probably want to start looking into external antennas and signal amplifiers. If you know the direction of the cell tower you’re connecting to, a high-gain Yagi or log-periodic antenna will help your reception. I don’t know how much gear you’re willing to pack in/out, but you’ll need a pole, stand, or something similar to attach the antenna too. If you don’t know the location of the tower you’re connecting to, there are signal strength meters (more accurate than your phone), or you can call the cell carriers with the gps location you’d like to broadcast from and they can tell you the gps coordinates of the nearest tower. Here’s some links to external antennas:
If your bonded hotspot has MIMO capabilities, you’ll want to use either antennas that support that internally, or multiple antennas. Best of luck to you - RF is a fickle, fiendish Mistress.
https://i.imgur.com/niXIRNS.jpg
I am using these Yagi antennas: https://www.amazon.com/gp/product/B00RJQ8RGC/
Cables are from MPD digital. US made high quality and low signal loss. https://www.amazon.com/gp/product/B008B49AZI/
They work amazingly well providing significantly lower latency. Better than I ever had with Comcast...
Edit: Don't have any recommendations on external enclosures for I have been re-using old ones for my needs. I assume any should work just as well as long as it is of decent quality.