An analytical and experimental investigation of the radiation properties of the

-plane sectoral surface wave horn, excited in the

mode, is described in this paper. The surface wave horn antenna utilizing an unsymmetrical radial surface wave is described. The antenna consists of an inductively reactive horizontal surface coincident with the

plane of a cylindrical coordinate system (

). This surface is confined between two conducting walls located at

(where

is the flare angle of the horn). Given the flare length, variation of the on-axis gain of the horn is analytically investigated, and design procedure for determining optimum

, in order to obtain maximum on-axis gain, is indicated.