| Antennas are very important components in the wireless communication systems.Their performances affect the quality of communication directly. With the newdevelopment of wireless communication systems, there comes great demand ofmultiband and wideband antennas in compact size. Because of its special properties,fractal structures were applied in antenna designs soon. Due to its self-similarity andspace-filing characteristics, fractal could achieve the miniaturization and muti-bandperformance of the antennas. By tuning the parameters to adjust the resonatefrequencies, one can also realize broadband characteristics of the antennas.In this thesis, the author firstly introduced the rationale of fractal, some commonstructures of fractal and fractal antenna based on fractal theory. Secondly expoundsthe design theory of fractal microstrip antenna, and briefly introduced thecharacteristics of fractal microstripe antenna and feed technology and a number oftraditional analysis methods of fractal microstrip antenna. Then, Several most basicfractal structures like Koch, Tree and Minkowski are chosen to make up antennas anddiscussed the relationship between miniaturization and fractal dimension. Based onthe research of the monopole antenna theory, antenna with two passbands900MHzand1.8GHz are designed. And then, the experiment discusses the multiband essenceof Sierpinski carpet fractal microstrip.The last aspect of the research lies in muti-bandfractal antenna a designs.three kinds of muti-band antennas are designed based on thefractal theory in this dissertation. The first muti-band antenna employs a kind ofsimplified Cantor set fractal, which is fed by a coplanar waveguide. Sierpinski fractalstructures are applied in another muti-band antenna. Six Sierpinski fractal units areused to generate the Ultra-wide Bandwidth. And the third muti-band antenna cancover three frequency bands of IEEE802.11and WiMAX. The frequency bands ofthe antenna are flexible to control by tuning the radiuses of the sizes. |
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