Radiation characteristics of a circumferential leaky-wave antenna on a conducting cylinder

The residue series representation of the fields for an azimuthal leaky-wave antenna on a conducting cylinder is studied. It is shown that the zeroth term corresponds to the case of an omnidirectional antenna, it being understood that omnidirectional refers to the azimuthal plane only. For each term of the residue series, it is shown that two regions exist for the radiation fields in the elevation plane. Within one region, the fields exhibit the characteristic of real rays, while in the other, the fields are that of diffracted rays. If the radius of the cylinder is allowed to increase to infinity, such that the cylindrical surface approaches a plane surface, only the region in which the real rays exist remains. The existence of the two regions in the cylindrical case is, therefore, attributed to the curvature of the surface. It is shown that the boundary between these two regions forms a hyperboloid of one sheet and that, in the far field, it approaches a conical surface about the cylindrical axis. An omnidirectional antenna was designed and constructed. The radiation patterns show good agreement with theoretical predictions.