Variable permittivity dielectric material loaded stepped-horn antenna

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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.
3The integral equation is solved numerically via the method of moments [15],[16]. Thegeneralized reflection matrix of an aperture is combined with the generalized scatteringmatrix of the horn. This procedure yields the complex weighting coefficient of each modeat the horn aperture in terms of the power of the incident TE 10 mode. Furthermore, theresults are used to determine the input reflection coefficient of the antenna and radiationpatterns.In Chapter 3, the performance optimization routine is presented. Both, the loaded andthe empty horn antenna dimensions, are optimized independently in respect to the crosspolarizationand the aperture efficiency. To excite the higher order modes at the aperturewith proper amplitude, a stepped-horn antenna design is introduced. Using appropriatestep sizes, the desired amplitude of the modes can be implemented. The length of theuniform waveguide between the step and aperture is optimized in order to achieve in phaserelation of the propagating modes at the aperture to yield uniform phase distribution. Thisis important for improving the aperture efficiency and cross-polarization levels. Loadingantenna with dielectric material, without increasing the size, leads to an improvementof the gain characteristics. Introducing the different dielectric material in the taperedsection and step section of the horn result in additional parameter to control the inputreflection coefficient. The characteristics of a horn antenna loaded with dielectric materialare compared with those of an empty horn antenna in Chapter 4. The important result ofthis comparison is that loading the horn antenna with dielectric material increases the gainfor the entire bandwidth. In general, dielectric loading increases the reflection from theaperture, therefore the input reflection coefficient increases, too. However, step dielectricloading allows to keep the input reflection coefficient on the same level as the one of theempty horn antenna or even to reduce it to a smaller value in a narrow frequency band.The results for optimized stepped-horn antennas are presented. As expected, the apertureefficiency, cross-polarization and gain characteristics are improved by optimization. Apart
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 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 54 and 55: 40would be slight deviation from th
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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