  We analyze the phase offsets between RF chains of modern IEEE 802.11ac chips.
We investigate both the 2.4 and 5GHz bands on a per OFDM subcarrier level.
Results reveal that the phase offset between receive antennas is due to random
phase rotations semi-time-invariant with up to four possible values. Moreover,
it is frequency-dependent. We propose a simple algorithm, which allows us to
correct the phase offset on the fly without any calibration. As
proof-of-concept, we implemented Angle of Arrival (AoA) using MUSIC algorithm.
To achieve higher accuracy we stitched the thirteen overlapping 20MHz channels
available in 2.4GHz band together to effectively have a single 80MHz channel.
Results show very good AoA precision although only two receive antennas were
used.
