When cAP with double band with ac

RouterOS Wireless Networking
3

Now if you need it - the only way is build your own dualband AP.
Stationbox inspot + rb912/rb922 + minipci-e card
http://forum.mikrotik.com/t/fyi-photo-of-rb922-r11e-enclosure-stationbox-inspot/83375/26

dual-band WiFi for office