A broadband high-gain dielectric-coated horn antenna operating in two orthogonal TE10+TE/TM12and TE01+ TE/TM21mode sets to generate circularly polarized elliptical shaped beam is described. The aperture E-field distribution can be tapered by virtue of the higher order TE/TM modes to cause the E-plane far-field beamwidth approximately equal to H-plane beamwidth of the other orthogonal set of modes, resulting in low off-axis polarization axial ratio. Because of the tapered aperture field distribution, the radiation patterns will also have low sidelobe levels. The radiation characteristics together with the on-axis gain of the antenna are derived from an electric vector potential on the basis of the vector diffraction formula. Analytical results are established in good agreement with experimental results on radiation pattern and gain measurements. This antenna which can be used as a communication satellite antenna to illuminate efficiently an elliptical zone on the earth surface will offer better directivity, high on-axis gain, low sidelobe levels and low cost.