Does antenna calibration necessary in a TDoA system?

Dear all, I am developing a TDOA system which contains two anchors, one tag and one synchronization card.
I have found that when the tag locating at some points, the mean of the distance difference noise is not zero, the noise mean varies from 0.1m to 0.8m which is not acceptable.
But the strange thing is that the variance of the noise is very ideal. So, do you guys know what is the reason and, will antenna calibration useful in this situation?
Besides, the two anchors are totally the same (hardware and software). And, it is LOS propagation, at least it is ture to our human eyes.

Antenna calibration is always necessary for achieving a good ranging result. the tag’s antenna delay may not be so important in TDOA setup, but antenna delay difference between the sync anchor and normal anchor directly affects TDOA positioning accuracy. Besides, two uwb module with same hardware design may still have different antenna delay introduced in manufacturing process.