@Kevinski66 

Good day,

Thank you very much for your time and patience.

Sorry for the delay.

Since TL-MR6400 does not support mimo, so I could not make sure the mimo antennas would enhance the LTE signal;

And since we did not have any specific model recommended, there are some information for your reference:

The original antennas are 2 Detachable External 4G LTE Antennas and the Antenna Interface type is SMA-M,

Antenna Frequency  Range is 0.79GHz ~ 2.7GHz;

Thanks a lot.