A study of the radiation characteristics of corrugated E-plane sectoral horns is described. Assuming the corrugations to be infinitely thin and sufficiently close packed, impedance boundary conditions are imposed on the fields in the axial region of the horn and it is established that a separable modal solution of fields in terms of TE to z modes is possible for this geometry. The horn aperture field is determined in terms of cylindrical wave functions and the vector diffraction formula is used to analyze the far-field radiation patterns. Excellent agreement is obtained between the theoretically derived pattern with experimental results for horns supporting the balanced HE11 mode with small flare angles (2α0 ≦ 30°), designed using the theory presented. Bandwidth properties of the horn have been studied which may be used to advantage in designing a corrugated E-plane sectoral horn without much degradation of its radiation characteristics corresponding to the balanced HE11 made over a wide frequency bandwidth (1.5:1). Copyright © 1973 by The Institute of Electrical and Electronics Engineers, Inc.