Impact of antenna mutual coupling on WiFi positioning and angle of arrival estimation

WiFi positioning techniques based on signal angle-of-arrival measurements have good accuracy and are promising. In such systems, several antennas receive the signal and an angle-of-arrival is computed by comparison of signal phases. Existing algorithms use a simple geometric angle-to-phase model: geometric ray paths cause corresponding phase differences and the differences are a trigonometric function of the angle-of-arrival. The model considers the receiver antennas as independent. However, the assumption is rough for WiFi antenna systems. Distances between the receiver antennas are small, the antennas influence to each other. The antennas are coupled. In this paper, we study the impact of the WiFi antennas mutual coupling to angle-of-arrival estimations. Electromagnetic simulations and hardware experiments were performed for this purpose. Commercial-of-the-shelf modules were used for the experiments. It is shown by simulations and experiments that the antenna mutual coupling offsets the angle of arrival estimations about 5-10 degrees. Considering of the mutual coupling can reduce angle estimation errors and, as consequence, increase positioning accuracy.