The Antenna connectors of 4G LTE Router 300M are compatible with SMA.
To install a new 4G antenna on the router, you must unplug the device. Then you must unscrew the antenna located on the right side when looking at the rear of the device. Once this is done, you must screw the SMA connection cable of your new 4G antenna in this location.
Please note that the left antenna of the device only enables reception whereas the right antenna enables transmission and reception.