TheE‐plane radiation pattern has been measured at short distances and bothEandH‐plane patterns at relatively great distances from the mouths of several electromagnetic horns. Measured values are compared with values calculated by the Kirchhoff formula and in addition the distant patterns are compared with values calculated by the corrected formula due to Stratton and Chu.For the range of horn length and aperture considered, the Kirchhoff formula gives satisfactory agreement in theE‐plane for angles as great as twenty degrees and at distances as short as one foot from the mouth of the horn; theH‐plane predictions are not as satisfactory.