There was a thread about this (on Ax3, but the essence is the same) a few days ago:
http://forum.mikrotik.com/t/solved-is-it-mandatory-to-mount-antennas-on-hap-ac3/172910/1
The connector on Mikrotiks is a RP-SMA male (and the antenna has the corresponding female) so you will need an extension cable, example:
https://shop.marcomweb.it/en/shop-online/cables-patches/wifi-antenna-extensions/extension-cable-for-wifi-antenna-1-m-rp-sma-dettagli.html
Usually in similar situations one would however use an external base that has already a (short) length of cable, example:
https://www.wlan-shop24.de/magnet-base-for-wifi-antenna-with-rpsma-connector-2x2mimo