Variable permittivity dielectric material loaded stepped-horn antenna

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48al = 0.73A, b1 = 0.34A and aperture size is aA = 1.8A, bA = 0.77A and lengths,L = 80.2mm.Table 4.6 Optimization Values of Stepped-horn Antenna for Input Waveguide Size, al =0.73A, b1 = 0.34A and Aperture Size aA = 1.8A, bA = 0.77A.Figure 4.13-Figure 4.16 show the comparison results of the input reflection coefficient,gain, aperture efficieny and cross-polarization level for optimized dielectric loaded hornantennas and the empty horn antenna. It can seen that from Figure 4.13, optimized dielectricloading of the step region with εrg 1.2 leads to improved input reflection coefficientIΓl 0.03 in a relatively < wide band(9.6 to 10.35 GHz) compared to an empty hornIF < 0.1 throughout the band of 9.0-11.0 GHz. It is possible to get even further reductionof IΓl < 0.02 within a very narrow band around 9.2 GHz. Figure 4.14 shows that inclusionof a step region to an empty horn results of an increase of gain by 1 dB over the entire band.However further increase by additional 1 dB (2 dB overall) is observed in the presence ofdielectric loading. It was observed that gain performance of a fully loaded step-horn versusstep region only dielectric loaded horn were identical. Presence of a dielectric can beattributed to an increase in gain due to enhancement of the equivalent aperture size in termsof electrical dimensions.One of the goals for optimization was to reduce the cross-polarization characteristics.The presence of a step region helps to reduce cross-polarization by almost 5 dB, Figure4.15. Further, inclusion of a dielectric can be used to tune cross-polarization to desired
49—30 dB at the expense of significant narrowing of the frequency band. Similar effect wasobserved in Figure 4.16 in the aperture efficiency enhancement from 40% to 50% in averageover the band. Figure 4.17 shows the co- and cross-polarziation levels of test horn antennaand (εri = 1.2 5r² = 1.2) loaded stepped-horn antenna are presented at f = 10 GHz.To show the effect of optimization, amplitudes of x-component of aperture magneticfield and y-component of aperture electric field for test horn antenna and stepped-hornantenna are presented in Figure 4.18 to Figure4.21. It can be seen from Figure 4.18 andFigure 4.19that aperture field distributions of test horn antenna exhibits tapered nature ofthe aperture fields along x-direction due to TE 10 mode. As the step region included inthe horn antenna, tapered nature of the aperture fields tend to smooth out leading to moreuniform characteristics in x-direction, as seen in Figure 4.20 and Figure 4.21.As a second example in optimization, input waveguide section of the stepped-hornantenna is chosen as a i = 0.73A, b ¹ = 0.34A and aperture size is a A = 2A, bA = 0.82λ.Theoptimization is carried out at f = 10 Ghz. Four different optimization schemes wereexecuted to compare the effect of dielectric loading, (εri 1.0 and 5r² = 1.0), (εr]. = 1.4and εr2 = 1.4), .9(F= \--r¹ 1.4 and εr² = 1.2), (εri = 1.2 and εr1 = 1.4). Notice that for thisoptimization, both aperture size and dielectric constants, εri and 5r² are chosen larger thanthe first example. Optimized length of tapered section L ¹ , length of step waveguide sectionL², step dimensions a s and b8, according the optimization results are presented in Table4.7. It can be seen from Table 4.7 that smallest length of the overall stepped-horn antennacan accomplished by using (εri = 1.4 εrg = 1.4)) as expected. Optimized stepped-hornantennas are compared with empty test horn antenna. Test horn antenna is chosen such thathas the same aperture, same input waveguide size and same overall length of by optimizedantenna (εri = 1.0 5r² = 1.0). Therefore, its input waveguide dimensions are al = 0.73A,b¹ = 0.34A and aperture size is aA = 2A, bA = 0.82A and has a of length L = 91.1 mm.
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Copyright Warning & RestrictionsThe
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VARIABLE PERMITTIVITY DIELECTRIC MA
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APPROVAL PAGEVARIABLE PERMITTIVITY
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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 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 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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