A technique for obtaining pattern symmetry and low sidelobes from a TE11mode coaxial radiator

The radiation characteristics of a mode excited semi-infinite coaxial waveguide are examined. Kirchoff-Huygen analysis illustrates a pattern sensitivity to the transverse coaxial dimension ratio which can render the mode coaxial radiator unattractive for many antenna applications. A circular iris at the aperture of the coaxial waveguide is shown to provide radiation pattern improvement. Transverse aperture field distributions, obtained by modal analysis methods, lead to radiation patterns characterized by beamwidth symmetry and low sidelobes. Experimental verification of the pattern characteristics of the modified coaxial radiator are demonstrated as well as favorable agreement between computed and measured data.