Regarding mobile antennas, you will notice, that one of them has a label MAIN, the other has AUX.
The MAIN antenna is used for transmission and reception. The AUX antenna is dedicated for reception and diversity, which means, that it allows to improve connection quality and throughput, especially in the areas where the coverage is poor.
Beginning with the 802.11n WiFi standard, support for a new feature at the time called MIMO was introduced, which allows to use multiple spatial streams to increase data rates. I order to utilize this feature, more than one antenna is necessary. Due to the fact that the WLAN chip used in RUT950 has support for 2x2 MIMO, two WiFi antennas are used.