Variable permittivity dielectric material loaded stepped-horn antenna

2field uniformity and this results in higher aperture efficiencies than horns with fundamentalmode alone. Optimization routine is introduced to implement desired modes at the aperture.Rigorous theoretical approaches to analyze an empty horn were reported in the literatur[9]-[11]. In Chapter 2, as a mathematical model for dielectric loaded horn analysis, hybridnumerical approach is used. In the analysis, the overall geometry is separated into twoparts. The tapered region is divided into a number of rectangular waveguide sections filledwith lossless dielectric material. Change in a dielectric permittivity within each step hasbeen included in the mode matching analysis in the tapered region. The method of momentssolution is applied across the radiating horn aperture.Following the standard mode matching technique [12]-[14] all possible TE and TMmodes (both propagating and evanescent) in each section are taken in account and thetransverse electric and magnetic fields on both sides of junction are matched. A set ofsimultaneous matrix equations for each junction is obtained by making use of the orthogonalityof waveguide modes and the continuity of the transverse fields through an aperture and zerotangential electric field at conducting walls. The elements of these equations are coupledpower integrals of all the propagating and evanescent modes on both sides of the junction.The overall scattering matrix of the horn is determined by cascading the scattering matricesof the involved junctions, iteratively.It is known that significant mode generation and reflection may occur at the aperture.In accurate design of a horn antenna, the effect of the aperture should be included. In theanalysis of a junction of a dielectric loaded horn and free space, it is assumed initially thatthe horn is placed in an infinite metallic ground plane. To facilitate the analysis, equivalentfield distributions are assumed for the interior and exterior regions of the horn antenna, byclosing the aperture with a perfectly conducting plate having the same size and shape asthat of an aperture and introducing unknown surface magnetic currents on either side ofthe aperture. Next, the magnetic field boundary conditions are imposed at the aperture andthe integral equation is obtained with magnetic surface current distribution as an unknown.