The voltage at the terminal of each half of a phase-monopulse antenna is induced by the incident wave and by the electromagnetic fields scattered from the other half of the antenna. In phase-scanned arrays, the asymmetrical scattering by the antenna of the waves that are incident from a direction other than broadside introduces a tracking error into the system. A qualitative investigation of the cause of the pointing error indicates that the error is dependent on the spacing between the halves of the antenna and on the radiation and scattering patterns of the subarrays. Carter's formulas for mutual impedance are used to give a more accurate estimate of the magnitudes of the pointing error and error slope that are caused by the mutual scattering in arrays of dipoles. The results of the calculations for arrays of half-wavelength dipoles can also be used to describe the pointing error in arrays of slots on an infinite planar conductor, which serve as an approximation to slot arrays on a finite planar conductor.