New M.E. Thesis Submitted from ECE Student


A key component of a wireless link is the antenna which efficiently couples electromagnetic energy from the transmitter to free space and from free space to the receiver. A proper design of this part is necessary for the efficient coupling of the energy from the circuit to the free space and vice-versa. With the advances of wireless communication systems and increasing importance of other wireless applications, wideband and low profile antennas are in great demand for both commercial and military applications. Moreover, some of the applications also require that an antenna be embedded into the airframe structure. ‘Fractals’ were first defined by Benoit Mandelbrot in 1975 as a way of classifying structures whose dimensions were not whole numbers. Fractals represent a class of geometry with very unique properties that can be enticing for antenna designers. While Euclidean geometries are limited to points, lines, sheets and volumes, fractal include the geometries that fall between these distinctions. Therefore, a fractal can be a line that approaches a sheet. The line can meander in such a way as to effectively almost fill the entire sheet.
Fractal geometry involves a recursive generating methodology that results in contours with infinitely intricate fine structures. These contours are able to add more electrical length in less volume. For antennas, this means that we can reap the rewards of miniaturizing an antenna using fractals without paying the price of having to manufacture an infinitely complex radiator. The reason for this intricacy is that the fundamental building blocks of fractals are scaled versions of the fractal shape. In antenna theory, Fractals have appeared as fractal electrodynamics, in which fractal geometry is combined with electromagnetic theory for the purpose of investigating a new class of radiation, propagation and scattering problem. Method of synthesis and design of arbitrary fractal antennas is based on using special generating element. It is simple geometry fragment: segment of broken line, quadrate, triangle, circle, tree, more complicated figure, etc. Design iterative process of the fractal antennas is a replacement of every part of the base element by the whole generating element. There are three distinct features that are explored in this work for designing fractal antennas. First, the self-similar nature in the fractal geometry is utilized for operating a fractal antenna at various frequencies. For fractal geometries the input resistance of antennas are typically hard to match by coaxial probe feeding therefore I used two types of feeds Co-planar waveguide (CPW) feed and Microstrip line feed to the fractal design. Furthermore, the CPW is easily implemented on a single microstrip substrate without the ground plane. Unique feature of a CPW feed for a microstrip antenna is that the entire structure resides on the upper plane of the substrate. The Microstrip Line feed consists of printing a trace from and edge of the patch to the edge of the dielectric substrate. This makes the attachment of a connector very simple and can change the impedance of the antenna, allowing some matching to be performed. In the first stage I designed the Patch Antenna using Fractal geometry and then in the next stages, two types of feeds are applied to the geometry, respectively. The performance comparisons in terms of various antenna parameters are done for the two types of feeds. Comparison between results verifies the new design idea and characteristics.

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