AbstractImprovement of the radiation characteristics by the “nonaxisymmetrical aperture field distribution” is described. The aperture distributions in the horizontal and vertical planes are designed to be a low‐sidelobe type and a high‐efficiency type, respectively. As a measure of the degree of nonaxisymmetry, the ratio of the edge levels in the vertical and horizontal planes is introduced. The dependences of the degrees of improvement of the aperture efficiency and the wide angle radiation pattern upon the edge level ratio were studied and the amount of improvement was presented quantitatively.For example, the wide angle radiation level was reduced by about 15 dB by nonaxisymmetric aperture distribution with the aperture efficiency kept constant. On the other hand, if the wide angle levels were kept constant, the aperture efficiency was improved by about 0.4 dB with nonaxisymmetric distribution. In the case of an offset antenna, sidelobe levels in the wide‐angle region were increased from the numerical results with the aperture field method by the effect of the edge diffraction.The increase is shown to be less than 3 dB in the case of an offset angle of 60°. Moreover, the wide‐angle directivity can be improved in a certain region centered on the plane in which the attempt was made to achieve a low sidelobe level by means of a nonaxlsymmetric distribution. Possibilities and examples of widening or reducing this region and furthermore shifting it to the surface other than the horizontal one we