Range extension bluetooth stick


I would like to use iBeacons on my device and I have tested a USB Mini Bluetooth stick in my HA device. This actually works quite well. But the range is very low. As soon as the door to the server room is closed, I reach the iBeacon only a few meters.
Does anyone have a recommendation on which bluetooth deivce I should use to increase the range? Are there, for example, devices with additional antenna, etc.?