Hi,
I have a board with DWM1000 on it and trying to do TWR with 4 anchors.
I noticed that the range value changes a lot (up to 20cm) if i rotate the tag.
How can i calibrate the antenna if when tag is moving the calibration is different for each orientation?
You need to calibrate for your typical / expected angle or if you don’t have one then for the middle of the range.
This is one of the limiting factors on how accurate you can get the final position. In theory if you know the orientation of the anchors and the tag location then you can calculate and correct for the anchor antennas. For the tag you need to either use an average value or if you can infer orientation from direction of travel you can correct for it using that.
Or you go the route we picked and use a different antenna 
Thank you for the response.
Can you give me more information about what type of antenna did you choose to avoid this problem?
Thanks in advance.
We went with a custom monocone antenna, one side of the PCB was the antenna ground plane, the other had the DW1000 on. It gives us about as uniform pattern as you can possibly get for any heading and a reasonably uniform pattern over elevation for sufficiently large range.
We did also test some biconical antennas on cables, they worked well but gave more complications in terms of mounting.