How to capture 802.11 ac packets?

Hi, I am a research student and I am stuck!I need to capture 802.11ac packets with the radiotap header on a linux machine. I have a TP-Link 802.11ac enabled router, a linux laptop with 802.11ac card, and I am trying to capture from a desktop in monitor mode. But am unable to capture even the 802.11n packets as the HT field is always 0 and the packets are 802.11g. Can anyone please help me with that.