Variable permittivity dielectric material loaded stepped-horn antenna

CHAPTER 4NUMERICAL RESULTSIn Chapter 2, the hybrid numerical technique is presented to analyze stepped-horn antennaloaded with variable permittivity dielectric material. In this model, mode matching techniqueis used in step approximated tapered section of the horn modeled with NI uniform rectangularwaveguide sections. Hence, it is very important to choose the size of each waveguidesection, A/ = L/NI properly so that the pyramidal tapered section is accurately modeled.Choice of 30 steps per wavelength has been found to work well in numerical evaluations.As a first example, empty pyramidal horn antenna with input waveguide section sizeal = 0.675A, b1 = 0.3A and aperture size aA = 1.25A, bA = 0.5A, length of the taperedsection, L = 2.5A is considered. It is assumed that TE10 mode in an incident wave at theinput of the feed waveguide has a power density of 1 Watt/m² . Table 4.1 shows amplitudeand phase of reflection and transmission coefficient of TE10 mode and the total powerPtot, Ptot = Prad Pref where Pradand Pre f are radiated and reflected power densities,respectively. Total number of modes used in this example were 3. As it seen from Table4.1, A/30 waveguide section size is enough for convergence to until fifth significant digit.Notice that power conservation check is also satisfied for every waveguide section size.Same study is repeated for dielectric loaded horn antenna and the similiar results wereobtained as seen in Table 4.2. Notice that the wavelength, A inside the dielectric mediumis smaller than the wavelength of the empty horn, the number of waveguide section, NIshould be bigger compared to the empty one. As it was expected, power conservation is alsosatisfied for dielectric loaded horn antenna. However, there is a small difference comparedto the the empty horn antenna, decrease in the wavelengths necessitated to include higherorder modes which were excited at the aperture. Hence, the chosen total mode number41