The boresight axis of monopulse antennas represented by the minima in difference patterns is shifted with frequency due to symmetry and phase errors. Two measuring equipments are described, by which the very small boresight shifts can be determined. The measuring equipments have been tested by theoretical considerations and experimental methods. A measurement limit in error of about plus or minus 0.1 mrad is achieved. The influence of the used components on the measured quantity error evaluating the boresight shift is discussed.