There has been an ever-growing demand, in both the military as well as the commercial sectors, for antenna designs that possess the following highly desirable attributes: 1. Compact size 2. Low profile 3. Conformal 4. Multi-band or broadband
There are a variety of approaches that have been developed over the years, which can be utilized to achieve one or more of these design objectives. Recently, the possibility of developing antenna designs that exploit in some way the properties of fractals to achieve these goals, at least in part, has attracted a lot of attention.
The term fractal, which means broken or irregular fragments, was originally coined by Mandelbrot to describe a family of complex shapes that possess an inherent self-similarity or self- affinity in their geometrical structure. The original inspiration for the development of fractal geometry came largely from an in-depth study of the patterns of nature. For instance, fractals have been successfully used to model such complex natural objects as galaxies, cloud boundaries, mountain ranges, coastlines, snowflakes, trees, leaves, ferns, and much more. Since the pioneering work of Mandelbrot and others, a wide variety of applications for fractals continue to be found in many branches of science and engineering. One such area is fractal electrodynamics, in which fractal geometry is combined with electromagnetic theory for the purpose of investigating a new class of radiation, propagation, and scatter problems. One of the most promising areas of fractal-electrodynamics research is in its application to antenna theory and design.
Traditional approaches to the analysis and design of antenna systems have their foundation in Euclidean geometry. There have been considerable amounts of recent interest, however, in the possibility of developing new types of antennas that employ fractal rather than Euclidean geometric concepts in their design. We refer to this new and rapidly growing field of research as fractal antenna engineering. Because fractal geometry is an extension of classical geometry, its recent introduction provides engineers with the unprecedented opportunity to explore a virtually limitless number of previously unavailable configurations for possible use in the development of new and innovative antenna designs. There primarily two active areas of research in fractal antenna engineering. These include: 1.) the study of fractal-shaped antenna elements, and 2.) the use of fractals in the design of antenna arrays. The purpose of this article is to provide an overview of recent developments in the theory and design of fractal antenna elements, as well as fractal antenna arrays. The related area of fractal frequency-selective surfaces will also be considered in this article.
WHAT IS FRACTALS,
WHAT IS FRACTAL GEOMETRY?
The term "Fractal means linguistically "broken" or "fractured" from the Latin "fractus". Benoit Mandelbrot, a French mathematician, introduced the term about 20 years ago in his book "The Fractal Geometry of Nature". However many of the fractal function go back classic mathematics. Names like G. Cantor (1872), G. Peano (1890), D. Hilbert (1891), Helge von Koch (1904), W. Sierprinski (1916) Gaston Julia (1918) and other personalities played an important role in Mandelbrot's concepts of a new geometry.
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In the study of antennas, fractal antenna theory is a relatively new area. The term fractal was coined by the French mathematician B.B. Mandelbrot during 1970s after his pioneering research on several naturally occurring irregular and fragmented geometries not contained within the realms of conventional Euclidean geometry. Fractal geometry accurately characterizes many non-Euclidean features of the natural including the length of coastline, branching of trees and density of clouds and finds their application in many engineering field. Fractal shaped antenna is becoming useful way to design advanced antenna such as multiband antenna with approximately the same input or radiation characteristics for different frequency band.
DESIGNING OF FRACTAL ANTENNAS
A fractal antenna's response differs markedly from traditional antenna designs, in that it is capable of operating with good-to-excellent performance at many different frequencies simultaneously. Normally standard antennas have to be "cut" for the frequency for which they are to be used—and thus the standard antennas only work well at that frequency. This makes the fractal antenna an excellent design for wideband and multi-band
APPLICATIONS OF FRACTAL ANTENNAS
There are many applications that can benefit from Fractal antennas. Discussed below are several ideas where Fractal antennas can make a real impact. The sudden grow in the wireless communication area has sprung a need for Compact integrated antennas. The space saving abilities of Fractals to efficiently fill a limited amount of space create distinct advantage of using integrated fractal antennas over Euclidean geometry. Examples of these types of application Include personal hand-held wireless devices such as cell Phones and other wireless mobile devices such as laptops on Wireless LANs and network able Pad Fractal antennas can also enrich applications that include Multiband transmissions. This area has many possibilities ranging from dual-mode phones to devices integrating
Over view of antenna
A fractal antenna is an antenna that uses a fractal, self-similar design to maximize the length, or increase the perimeter (on inside sections or the outer structure), of material that can receive or transmit electromagnetic radiation within a given total surface area or volume.
Fractal antennas are also referred to as multilevel and space filling curves, but the key aspect lies in their repetition of a motif over two or more scale sizes,or "iterations". For this reason, fractal antennas are very compact, are multiband or wideband, and have useful applications in cellular telephone and microwave communications.
The first fractal "antennas" were, in fact, fractal "arrays", with fractal arrangements of antenna elements, and not recognized initially as having self-similarity as their attribute. Log-periodic antennas are arrays, around since the 1950s (invented by Isbell and DuHamel), that are such fractal arrays. They are a common form used in TV antennas, and are arrow-head in shape.
An example of a fractal antenna: a space-filling curve
The physical size of the antenna is unrelated to its resonant or broadband performance.
Fractal element antennas are shrunken compared to conventional designs, and do not need additional components.
Electrical resonances may not be directly related to a particular scale size of the fractal antenna structure.
Advantages of fractal
better input impedance matching
wideband/multiband (use one antenna instead of many)
frequency independent (consistent performance over huge frequency range)
reduced mutual coupling in fractal array
• gain loss
• numerical limitations
APPLICATIONS OF FRACTALANTENNAS
Applications include in personal hand held wire less device such as laptops on wireless LAN.
It can also enrich application that include multiband transmission.
Dual mode phone to device integrating.
Many variations of fractal geometries have been incorporated into the design of antennas. Further work is required to get an understanding of the relationship between the performance of the antenna and the fractal dimension of the geometry that is utilized in its construction.