Variable permittivity dielectric material loaded stepped-horn antenna

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40would be slight deviation from this value, but it has been checked that this difference issmall enough to not to change the overall design procedure.The complete optimization steps are:- Define the input waveguide dimensions a 1 ,b 1 and the aperture dimensions aA and bA,- Define dielectric constants, εl and ε2,- To determine step dimension a 8 , calculate step ratio a from (3.5), Since H-plane stepis used in this example, b, remains same as bA- Calculate the length L2 so that TEm and TE30 modal coefficients are in phase. Notethat at the step discontinuity, TE m mode excites TE30 mode out of phase 180°,- Determine the length L 1 so that overall reflection of the TE10 mode along the taperedsection includes step discontinuity and reflection of TE 10 mode from the apertureshould be 180° out of phase at the feed waveguide plane to minimize the input returnloss.Since formulas used in the optimization routine are quite simple, it is very fast toobtain results unlike the commercial optimization software tools. However, numericalelectromagnetic simulators can be exploited to optimze overall solutions which may includehigher order modes higher than the TE30 mode.
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
Page 1 and 2:
Copyright Warning & RestrictionsThe
Page 4 and 5: VARIABLE PERMITTIVITY DIELECTRIC MA
Page 6 and 7: APPROVAL PAGEVARIABLE PERMITTIVITY
Page 8 and 9: To my parents, ..Tahsin and Güler
Page 10 and 11: TABLE OF CONTENTSChapterPage1 INTRO
Page 12 and 13: LIST OF FIGURESFigurePage2.1 Geomet
Page 14 and 15: FigureLIST OF FIGURES(Continued)Pag
Page 16 and 17: 2field uniformity and this results
Page 18 and 19: 4from improving the gain, dielectri
Page 20 and 21: Figure 2.1 Geometry of pyramidal a
Page 22 and 23: 84Figure 2.4 Step discontinuity bet
Page 24 and 25: 10section asFrom (2.4), the transve
Page 26 and 27: 12and for the magnetic fieldIn the
Page 28 and 29: 14where * shows complex conjugate.
Page 30 and 31: 16where D is a diagonal matrix of t
Page 32 and 33: 18Figure 2.6 Generalized reflection
Page 34 and 35: 20aperture region and 11Ps is the m
Page 36 and 37: 22where T; (x) and T: (y) are trian
Page 38 and 39: 24where Γwghnk and r wg enk are th
Page 40 and 41: tiTo determine the unknown coeffici
Page 42 and 43: 28An electric vector potential F an
Page 44 and 45: 30Using midpoint rule to evaluate i
Page 46 and 47: 32whereGreen function integrals, 4,
Page 48 and 49: 34taper and the phase distribution
Page 50 and 51: 36Even though, TE10 mode is an inci
Page 52 and 53: 38satisfy the amplitude ratio of 1/
Page 56 and 57: 42increased to 15. Scattering matri
Page 58 and 59: 44Table 4.4 Amplitude and Phase of
Page 60 and 61: 46Figure 4.3, it is obvious that th
Page 62 and 63: 48al = 0.73A, b1 = 0.34A and apertu
Page 64 and 65: 50Table 4.7 Optimization Values of
Page 66 and 67: Figure 4.3 Input reflection coeffic
Page 68 and 69: Figure 4.5 Aperture efficiency vers
Page 70 and 71: Figure 4.7 Input reflection coeffic
Page 72 and 73: Figure 4.9 Aperture efficiency vers
Page 74 and 75: Figure 4.11 E-plane pattern versus
Page 76: 62Figure 4.13 Input reflection coef
Page 79 and 80: Figure 4.16 Aperture efficiency ver
Page 81 and 82: Figure 4.18 Amplitude of aperture m
Page 83 and 84: Figure 4.20 Amplitude of aperture m
Page 85 and 86: Figure 4.22 Input reflection coeffi
Page 87 and 88: Figure 4.24 Cross-polarization leve
Page 89 and 90: 751Figure 4.26 Amplitude of apertur
Page 91 and 92: 770.8Figure 4.28 Amplitude of apert
Page 93 and 94: Figure 4.30 Amplitude of aperture e
Page 95 and 96: 81Dielectric materials of various p
Page 97 and 98: The indefinite integrals associated
Page 99 and 100: BIBLIOGRAPHY[1] P. Clarricoats, A.
Page 101 and 102: 87[26] T. Bird and S. Hay, "Mismatc
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Variable permittivity dielectric material loaded stepped-horn antenna

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