The Minew AR1 locator has multiple antenna that receive special constant tone extension (CTE) advertising from beacons.
The Minew antenna consists of 12 PCB patches. If you imagine a radio signal hitting the antenna array from the left hand side, the antennas to the right will receive the signal slightly later. The phase difference can be use to determine the angle.
Martin Woolley’s excellent Bluetooth Direction Finding Technical Overview explains the theory. The main concept is based on simple trigonometry:
In practice, if you do this across just two antenna and with one sample the result has very poor stability. Instead, you need to consider all the antenna patches, over time, as well as perform analysis in multiple directions. This requires use of advanced radiogoniometry techniques.