Microwave metamaterials for compact filters and antennas
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- Tez No: 400836
- Danışmanlar: DR. HEINO HENKE
- Tez Türü: Doktora
- Konular: Elektrik ve Elektronik Mühendisliği, Electrical and Electronics Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 2012
- Dil: İngilizce
- Üniversite: Technische Universität Berlin
- Enstitü: Yurtdışı Enstitü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 129
Özet
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Özet (Çeviri)
Materials with simultaneous negative permittivity and permeability in a certain frequency band were first studied by Veselago in 1968. He termed such media left-handed media due to the left-handed triad formed by the electric field, magnetic field and the phase propagation vector. Because of the inexistence of such materials in nature, the optical and electromagnetic consequences examined in Veselago?s work could only be observed after nearly 30 years. In 2000, a composite material, also known as a metamaterial, consisting of periodic negative permittivity and permeability cells in the form of metallic wires and split rings was shown to exhibit left-handed properties. Because the dimension of the rods and rings are small compared to the operation wavelength, it is possible to approximately describe their bulk electromagnetic properties using an effective permittivity and permeability. In this thesis, the fundamental properties of negative permeability, permittivity and left-handed materials are explored in the antenna and filter design as potential microwave applications. As an investigation on basic properties and alternative design methods of metamaterials, artificial magnetic materials are examined at first. Artificial magnetic materials in the form of metallic cylinders with/without splits and split ring resonators are studied. Approximate effective permeability formulations are derived. Numerical calculations for the transmission and reflection parameters of concentric cylinders with splits are carried out in addition to analytical calculations. The good agreement between analytical and numerical calculations is confirmed. The resonance frequency of split ring resonators is also approximated with an alternative formulation derived from quasi-static analysis. It is shown that the numerical calculations agree better with the derived formulation than the original formulation. 1D dispersion diagram of split ring resonators is also examined numerically. Effective material parameters are retrieved to confirm Lorentzian-type frequency dependence of permeability. As an investigation for more homogenous material design, a fractal spiral resonator is studied as a unit cell of negative permeability material. It is confirmed that the composite material has negative permeability between the magnetic plasma and resonance frequency with capacitive wave impedance. At second, artificial dielectrics composed of periodic metallic wires are examined with analytical and numerical calculations. It is shown that the effective permittivity of wire array has Drude type frequency dependence and is negative at the frequencies smaller than the plasma frequency. The numerical and analytical calculations are in good agreement. To design more homogeneous metamaterials, a fractal anti-spiral resonator is examined as a unit cell of negative permittivity material. It is pointed out that the composite material has negative permittivity between the electric plasma and resonance frequency with inductive wave impedance. As a last investigation on metamaterial fundamentals, the design of left-handed materials is explored. The eigenmode equation of a rectangular waveguide, which is periodically loaded with negative permittivity and permeability cells is analytically and numerically calculated. Both are in good agreement. In addition, a conventional LHM unit cell is numerically studied. It is confirmed that the LH transmission band is the overlapping region of negative permittivity and permeability bands. A compact cell geometry based on wire loading of spiral resonators is studied as an alternative to the conventional cell designs. It is deduced from the numerical calculations that it can be used in the design of more homogeneous LH materials. Next, two potential microwave applications are explored. The first application is antenna design. Two meta-antennas are examined. The first antenna is a broadband dipole antenna, which is designed by loading the dipole element with LHM cells in an array form. The broadband operation is confirmed by experimental and numerical results. It is shown from the surface current distribution and radiation patterns that LHM cells are radiating with a lower gain in comparison to the dipole antenna. In addition, it is deduced from the numerical results that to adjust the phase difference per unit cell can be one solution to increase the radiation efficiency and antenna gain. Possible gain enhancement methods are pointed out, one of which is used in the design of the second antenna. It is a microstrip slot antenna. It is designed with electric and magnetic dipoles in the form of slotted metamaterial cells in the radiator. It is confirmed numerically that the antenna is narrowband with high radiation efficiency and gain. The second application is the filter design. Two meta-filters are examined. The first filter is a compact band-stop filter. It is designed by directly connecting four LHM cells in the form of ?/4 resonators with the feeding line. The bandstop characteristics are confirmed by experimental and numerical results. The second design is a compact band-pass filter, which is designed by coupling two unit cells directly connected with the feeding line. It is shown numerically that low insertion loss and high selectivity can be achieved by optimizing the field coupling among the resonators. One advantage of both filters is that there is no need of a matching network, which therefore reduces the filter size significantly.
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