Estimation bias variation on beamformed signals

Digital beamforming is widely used for estimating the direction of arrival (DOA) of signals incident on an array of antennas. It is well known that conventional beamforming has limited spatial resolution determined by the aperture of the array. It is also known that multiple signals incident on the array "bias" the DOA estimates of every other incident signal. A periodic wobbling of the DOA estimated by beamforming has been noticed on a number of systems, the authors prove that the periodic wobbling is due to the phase difference between the signals incident on the array which, due to their differing temporal frequencies, results in the periodicity of wobble described.