Xbee Pro 868 Antenna

Hi there,
i have seen from the datasheet that is possible to use high gain antennas with xbee pro 868 such as yagi,… Where can i find some infos about the antennas written in Appendix C of the datasheet?
Thanks for replies,
Alessandro

http://www.taoglas.com/antennas/Wi-Fi_Zigbee_WLAN/External_-_2.4GHz_YAGI_Antennas/

Is it OK to use a 2.4GHz antenna for a 868/900MHz device?