The Use of Fractals and Non-Foster Circuits for Wideband Metamaterials and Antennas
1 online resource (139 pages) : PDF
University of North Carolina at Charlotte
Implementations of two methods for broadening the performance bandwidth of resonant electromagnetic structures are presented. The first method is the use of non-Foster loading elements, and the second method is the use of fractal geometries. Non-Foster loading is used in the context of negative permittivity and negative permeability metamaterials. A capacitively loaded strip unit cell with non-Foster loading is presented and the effects of parasitic resistances in the non-Foster element are explored, as well as the effect of variations in the test fixture. The unit cell is shown in simulation and measurement to exhibit sub-unity permittivity over a 133% bandwidth. A split ring resonator unit cell with non-Foster loading is presented next. The effects of parasitic resistance in the non-Foster element and variations in the test fixture are demonstrated for this unit cell, and the structure is shown in simulation to exhibit negative permeability over a bandwidth of 100%. Fractal geometries are utilized next, first in the context of a negative permittivity metamaterial unit cell, and then in the context of 3D-printable monopole antennas. The fractal metamaterial unit cell is shown to exhibit negative permittivity over a bandwidth of 6.4% in a coaxial test fixture, which is estimated, based on simulations, to correspond to a bandwidth of 32.9% in free space. Two fractal antennas are presented. The first is based on a branching cube pattern and is shown in simulation to have 181% bandwidth and poor polarization at high frequencies. The other is based on a branching cone pattern and shown in simulation and measurement to have ~180% bandwidth, and in simulation to have considerably better polarization than the cubic version.
FRACTALSNEGATIVE PERMEABILITYNEGATIVE PERMITTIVITYNON-FOSTER LOADINGWIDEBAND ANTENNASWIDEBAND METAMATERIALS
Weldon, ThomasMiri, Mehdi
Thesis (M.S.)--University of North Carolina at Charlotte, 2015.
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