The spatial (three‐dimensional) radiation characteristics of directive antennas are often needed in radio interference calculations and predictions. Presented is a method that allows a fast computation of the spatial radiation envelope characteristics of antennas from measured pattern information. This is achieved by fitting the measured data to simple functional forms that are based on salient physical properties of the antennas. An example is given in which radiation envelopes for a pyramidal horn‐reflector antenna, widely used in AT&T service, are calculated from measured data. Superpositions of quadratic functions to fit main radiation lobes and logarithmic functions to represent the side‐lobe envelopes are being used, and good agreement with the measured data is demonstrated.