Direction of Arrival (DoA) for 180 degree phase ambiguity RFID UHF Reader: Limits and perspectives

Recently, Phase Difference of Arrival (PDoA) has been tremendously used to detect Direction-of-Arrival (DoA) of RFID UHF Tags because of its accuracy and robustness in difference environments. However, most of the methods just use RFID Reader with phase range from 0 degree to 360 degree instead of 0 degree to 180 degree which is the case in most of the Commercial off-the-shelf (COTS) RFID Readers. In this paper, some problems of DoA estimation will be introduced when using RFID Reader with range of 180 degree: first, coupling when placing antennas too close; second, phase ambiguity. Real experiments will also be introduced to prove the results.