29-09-2011, 07:30 AM
plz send me report & presentation on fractal antenna which should contain basics of fractals,random & deterministic fractal, proposed antenna geometry etc...
29-09-2011, 07:30 AM
plz send me report & presentation on fractal antenna which should contain basics of fractals,random & deterministic fractal, proposed antenna geometry etc...
29-09-2011, 09:38 AM
to get information about the topic"fractal antenna" please refer the link bellow
https://seminarproject.net/Thread-fractal-antennas https://seminarproject.net/Thread-fracta...unications https://seminarproject.net/Thread-fracta...pplication
16-01-2012, 10:32 AM
to get fractal antenna ppt, explanation and related topics link page bellow
https://seminarproject.net/Thread-fractal-antennas https://seminarproject.net/Thread-fracta...unications https://seminarproject.net/Thread-fracta...pplication https://seminarproject.net/Thread-super-...nna-design
29-06-2013, 04:30 PM
Fractal Antenna
Fractal Antenna.docx (Size: 871.9 KB / Downloads: 21) INTRODUCTION A fractal is a rough or fragmented geometric shape that can be split into parts each of which is (at least approximately) a reduced-size copy of the whole a property called self-similarity. Roots of mathematically rigorous treatment of fractals can be traced back to functions studied by Karl Weierstrass, Georg Cantor and Felix Hausdorff in studying functions that were analytic but not differentiable; however, the term fractal was coined by Benoît Mandelbrot in 1975 and was derived from the Latin fractals meaning "broken" or "fractured." A mathematical fractal is based on an equation that undergoes iteration, a form of feedback based on recursion Fractal antenna theory is built, as is the case with conventional antenna theory, on classic electromagnetic theory. Fractal antenna theory uses a modern (fractal) Geometry that is a natural extension of Euclidian geometry. In this report, attention is called to this developing, but already quite large, field of study. In the brief study of fractal antennas for this report, I have found hundreds of papers, dozens of patents and several established companies manufacturing and selling products. Currently Dwight Jagged of the University of Pennsylvania and Douglas Werner of Pennsylvania State University and a handful of others are preaching the gospel. In this article, we describe a successful area that meets this need, which uses fractal geometry for better antennas. Such fractal antennas have multiple bands or are genuinely wideband. They may replace a suite of antenna systems, disposing of tuning and matching circuitry, and fit in unique or constrained form factors. Fractals are complex geometric designs that repeat themselves, or their statistical proper-ties on many scales, and are thus “self similar.”Fractals, through their self-similar property, are natural systems where this complexity provides the sought-after antenna properties .The first use of fractals as antennas was called “fractal loading,” which uses bends, or holes, over a variety of size scales to emulate the effects of discrete inductors and capacitors. FRACTAL ANTENNAS 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. Such 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. A good example of a fractal antenna as a space filling curve is in the form of a shrunken fractal helix. Here, each line of copper is just small fraction of a wavelength. 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 multiband applications. Since they were first described by the French mathematician Benoit Mandelbrot in the mid-1970s, repeating geometric figures known as fractals have fascinated computer scientists, mathematicians and graphic artists. These "broken curves" have been used to explain naturally-occurring phenomenon such as lightning, galactic clusters and clouds. Many computer-image compression schemes are based on fractals. Until recently, however, there have been few hardware applications of fractal geometry. Fractal antennas and fractal arrays are notable exceptions. HISTORY & BACKGROUND Antenna theory considers three classes of radiators in terms of frequency coverage: (1) narrowband: – small range of the order of a few percent around the designed operating frequency. (2)wideband or broadband:- covers an octave or two. (3)frequency independent (a misnomer): – about a ten to one or greater range of frequencies. Any good antenna text talks about antenna scaling, that is the properties (impedance, efficiency, pattern, etc.) remain the same if all dimensions “Fractal Antennas “scaled by the same factor. we come upon the amazing realization that a fractal shaped metal element can be used as an antenna over a very large band of frequencies. A typical book would say something like, “A distinguishing feature of frequency independent antennas is their self-scaling behavior”. But then go on to say, Frequency independent antennas can be divided into two types: spiral antennas and log-periodic antennas A fractal is a rough or fragmented geometric shape that can be subdivided in parts, each of which is (at least approximately) a reduced-size copy of the whole. Fractals are generally self-similar and independent of scale. Fractals also describe many real-world objects, such as clouds, mountains, turbulence, and coastlines that do not correspond to simple geometric shapes. OVERVIEW OF FRACTAL ANTENNA An antenna can be defined as any wire, or conductor, that carries a pulsing or alternating current. Such a current will generate an electromagnetic field around the wire and that field will pulse and vary as the electric current does. If another wire is placed nearby, the electromagnetic field lines that cross this wire will induce an electric current that is a copy of the original current, only weaker. If the wire is relatively long, in terms of wavelength, it will radiate much of that field over long distances. The simplest antenna is the “whip”. This is a quarter wavelength wire that stands above a ground plane. The most common examples are found on automobiles and are used for broadcast radio, CB and amateur radio, and even for cellular phones. This design goes back to the 1890's when Marconi set out to prove that radio signals could travel long distances. To be successful, he had to stretch a long wire above the ground. Due to the low frequencies, thus a long wavelength, the wire had to be long. He also found that the wire worked better when it was high above ground. RADIATION PATTERN:- Radiation is maximum when broadside, or perpendicular to a wire, so a vertical whip is ideal for communication in any direction except straight up. The radiation “pattern”, perpendicular to the whip, can be described as omni-directional. There is a "null", or signal minimum, at the end of the whip. With a less than ideal antenna, such as a bent or tilted whip, this null may move and partly disappear. It is important to know the radiation pattern of the antenna, in order to insure that a null is not present in the desired direction of communication. THE WHEELER CAP METHOD:- The Wheeler cap method is an accurate, fast, and easy to implement technique for the measurement of radiation efficiency and quality factor of electrically small antennas. • The Directivity/Gain method (in the near-field) can be also used to assess the measured results obtained with the Wheeler method because a measurement facility is accessible and measurement times are reasonable. • A random positioner allows accurate measurement of antenna efficiency and maximum gain. • Near field measurements show the field concentration at small parts of the antenna, typical from pre-fractal structures. • Standard techniques for the fabrication of printed circuit boards are also useful for the manufacture of pre-fractal designs (technique used at UPC). MEASUREMENT OF SMALL ANTENNAS RADIATION PARAMETERS:- The EPFL partner has setup an unique facility for the measurement of small antenna parameters, in particular, loss efficiency and gain. Electrically small antennas are difficult to measure properly because they are neither purely symmetrical nor asymmetrical due to the limited size of ground planes or feeding baluns. Therefore, when the antenna is connected to a measuring device, a current flows in the outer conductor of the cable connecting the antenna, creating spurious radiation that completely masks the characteristics of the antenna under test. In order to overcome this problems, an original solution based on a random positioner has been developed. Small antennas gain and loss efficiency can be accurately measured with the proposed solution. PRE-FRACTAL ANTENNA PROTOTYPES:- In this report three different families of microwave fractal-shaped devices are studied. The first two are based on well-known fractals, one is a surface fractal, the Sierpinski gasket, and one is a line fractal, the Koch curve, while the third is a new structure based on capillary filters. The previously existing literature studies the Sierpinski as a monopole, as well as a patch. In the current contribution the measurements of a Sierpinski printed antenna are presented. The gaskets have been printed on a copper-berilium layer. To end the construction of these antennas the gaskets are going to be glued to a substrate of εr=1.07 and h=2mm and to a ground plane. The sticking process is going to be done with the help of a thin film of glue in order not to affect the permittivity of the substrate. The ground plane, the substrate, the film of glue and the gaskets are stacked and kept together with the help of two aluminum plates screwed tight. |
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