Design of metamaterials and applications to microwave antennas

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Supervisor:
Dr. Szabó Zsolt
Department of Broadband Infocommunications and Electromagnetic Theory

Since the famous articles of Pendry et al. ([1], [2], [3]) a very intensive research started in the topic of metamaterials. Since then, a lot of applications were also proposed in a variety of fields. Some examples in the field of microwave technology are special waveguides [5], cavity resonators with reduced size [6], and microwave lenses for antennas [7]. This document belongs to the latter group, as it explains the design of a flat metamaterial lens, made for a C bad microwave antenna.

In the first part, a general description of metamaterials can be found. Firstly there is an explanation of the properties of zero index metamaterials, involving how they can be used as microwave lenses. Secondly an analysis of three particular metamaterial structures is given: split ring resonators (SSR), continuous wires and closed square rings (CSR). This section has two simultaneous roles: shows how the extreme electromagnetic properties can be achieved using metamaterials, and explains the analytical methods used for describing metamaterials. At the end of the first part, the homogenization and extraction of effective material parameters, which uses the transmission and reflection coefficients of layered metamaterials as input data is also presented. The homogenization is a very important design tool of the metamaterial design, because it is possible to measure or simulate the scattering parameters, making the design process verifiable and reproducible.

Then a short description of the design and the characteristics of the horn antennas is given, which is followed by the explanation of the design methods applied in this thesis.

The design principles of a zero refractive index metamaterial lens is described. The first stage of the design procedure determines the initial geometric parameters of the metamaterial. This geometry is used as the initial arrangement of the metamaterial lens, which is further optimized with finite difference time domain (FTDT) electromagnetic field simulator connected to genetic algorithm of optimization. The details of this procedure are presented.

Secondly a gradient index lens is designed which is built of CSR elements. The relation between the geometric parameters of the cell and between the index of refraction is determined with the effective material parameter extraction method [9] described also in section 3.2. The refractive index distribution along the aperture is arranged to provide near zero phase deviation along the aperture. Despite that the electromagnetic coupling of the cells arranged in a homogeneous cell matrix behaves different than the inhomogeneous cell matrix, this design method also gives an adequate result.

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