Radiation Patterns of Shielded Dielectric Horns: Analytical Versus Simulation Approaches

The theory of the dielectric cone antenna has been known since the early seventies. On their own, this antenna has a reasonably circular symmetric radiation pattern but exhibits an undesirably high side-lobe level. A properly designed metallic shield, which does not interfere with the field structure of the dielectric cone, may be used to reduce the side-lobe level. Although in principle this antenna should be quite broadband, prototypes show that this is not the case. After proving that the metallic shield performs as expected, aperture phase error and wave impedance mismatch at the aperture were identified as the main disturbing factors. A lens placed at the aperture corrects the phase error and a λ/4 matching layer on the lens surface improves aperture matching. The result is an antenna with an almost circular symmetric radiation pattern, -27 dB side-lobe level and ±4 % bandwidth.