Wideband bearing estimation with compensation for mutual coupling effects

It is frequently of interest to determine the angle of arrival of two signals. This is usually done by assuming that the incident fields are uniform plane waves and that there is no mutual coupling between the antenna elements. However, if the two incident signals have a small angular separation the mutual coupling may cause errors in the angle of arrival calculations. We present a method of compensating for this coupling so that the angles of arrival may be correctly determined. The antenna array used for direction finding is usually designed to operate over a wide band of frequencies. At the highest frequency of operation, the antenna elements are separated by half a wavelength or less. This prevents the formation of grating lobes at all frequencies of interest. This criterion, however, causes significant coupling between the antenna elements which increases as the frequency is decreased. The mutual coupling degrades the actual signal and the performance of the direction finding algorithm. We use the multiple signal classification (MUSIC) algorithm to correct for this coupling, the actual signal is multiplied by a "terminal impedance matrix" derived from the method of moments (MoM) impedance matrix. The corrected signal is much closer to the ideal signal. Therefore, the minimum resolvable angular separation between two signals approaches that of the ideal input with no coupling effects present.