Variable permittivity dielectric material loaded stepped-horn antenna

CHAPTER 3PERFORMANCE OPTIMIZATIONThe optimization objective is to reduce cross-polarization and improve aperture efficiencycharacteristics of a horn antenna. Figure 3.1 shows the proposed stepped-horn antennaconfigurations subjected to optimization. Stepped-horn antenna consists of three majorsections:- Tapered region of length L 1 ,- Symmetrical step on the horn wall,- Uniform waveguide region of length L2 between step and the aperture.The cross-polarization characteristics depend on the difference between the E— and H—plane patterns. If identical E— and H— plane aperture field distributions can be realized,it would result in minimized cross-polarization level. Aperture efficiency is a measurehow efficiently the physical area of the aperture is utilized. Since gain linearly depends onthe aperture efficiency, improving the aperture efficiency implies an increase in gain, too.Aperture efficiency is mainly a function of the aperture field amplitude taper and phasedistributions. Maximum efficiency can be achieved by excitation of uniform amplitudeand phase distribution over the aperture. Therefore, if identical uniform field distributionsalong the E- and H- plane can be implemented, both cross-polarization level and apertureefficiency characteristics can be improved simultaneoulsy. For uniform aperture field distributionacross the aperture, T M modes should not be present and also T Emn, modes where n 0should not be exited. TEm0 modes should have an approximate amplitude relation of 1/mto satisfy the uniform aperture field distributions as35