@Richelieu 

Hello, the two external antennas are 4G LTE antennas, they are different from the ordinary wireless antennas. These antennas are mainly used to receive 4G signals from your mobile ISP by auxiliary SIM card. It’s not recommended replacing them, because the antenna is only used as an auxiliary, and the strength of 4G signal mainly depends on SIM card and ISP.

If you think the 4G LTE antennas are not good enough to receive signals and want to change one or two, please read the following carefully:
1). If you still want to change the 4G LTE antenna, you need to change the two at the same time, and the two replacement antennas should have the same specifications. If you only change one of them, it will not achieve the desired effect, but the effect may be worse.
2). For the replaced antenna, the interface type needs to be matched. The interface type of the two external antennas is SMA plug, that is SMA male, not ordinary RP-SMA.
3). The frequency range supported by the replacement antennas should be the same as the original antennas.
4). The distance between the two replacement antennas shall not be less than the distance between the original antennas.

Hopefully, that answers your question but let us know if you need more details.