Showing papers on "Fractal antenna published in 1999"

Fractal antenna engineering: the theory and design of fractal antenna arrays

Abstract: A fractal is a recursively generated object having a fractional dimension. Many objects, including antennas, can be designed using the recursive nature of a fractal. In this article, we provide a comprehensive overview of recent developments in the field of fractal antenna engineering, with particular emphasis placed on the theory and design of fractal arrays. We introduce some important properties of fractal arrays, including the frequency-independent multi-band characteristics, schemes for realizing low-sidelobe designs, systematic approaches to thinning, and the ability to develop rapid beam-forming algorithms by exploiting the recursive nature of fractals. These arrays have fractional dimensions that are found from the generating subarray used to recursively create the fractal array. Our research is in its infancy, but the results so far are intriguing, and may have future practical applications.

Multiband and wideband properties of printed fractal branched antennas

Abstract: Multiband and wideband properties of printed fractal branched antennas The presented numerical and experimental results show that the input reflection coefficient relative to 50 Ω of a fractal tree antenna exhibits a multiband behaviour generated by the elements of successive iteration levels as well as a wideband response produced by the large number of elements of the last iteration level.

Fractal stacked monopole with very wide bandwidth

Abstract: A parallel feed stacked fractal antenna using the square Sierpinski and diamond Sierpinski carpet is introduced. The design achieves a good input impedance match throughout the passband (1-20 GHz) but occasional slight mismatch occurs. Three different experimental results are shown and the measured gain of these antennas is generally >0 dBi. These antennas are suitable for applications in picocell environments for the operating bands of GSM, DECT and WLAN systems.

Radiation characteristics of thin-wire ternary fractal trees

Abstract: The multiband electromagnetic behaviour of thin-wire structures based on a ternary tree fractal geometry are investigated. As an example, experimental and numerical results are presented for the particular case of a three-band monopole structure, which show the expected self-similar behaviour at those bands. Some interesting properties are observed for these ternary tree fractal structures that are not evident in their Sierpinski monopole counterparts.

Multiband characteristics of two fractal antennas

Abstract: Experimental results show a multiband behavior for the Sierpinski gasket fractal antenna and the tree-like fractal antenna. Such behavior has been explained by the fractal structures of the antennas. We show that the matched frequencies possess a log-periodic behavior. ©1999 John Wiley & Sons, Inc. Microwave Opt Technol Lett 23: 242–245, 1999.

Fractal loop antenna

Abstract: A reduced size wideband antenna operates at multiple frequency bands. The antenna is formed from a plurality of fractal elements either cascade connected, series connected or parallel connected. The fractal elements of the antenna structure repeat a specific geometric shape.

Fractal arrays based on iterated functions system (IFS)

Abstract: Fractal arrays have been suggested, mostly in order to obtain some kind of self-similar features in the radiation patterns. This, in turn, will allow a multi-band frequency usage of the array. Most of the previous work done in this area deals with fractal arrays in which the distance between the elements is some fractal function (like the Cantor set), whereas their amplitude is constant. This work, on the other hand, deals with uniformly spaced elements, whereas the elements amplitude distribution is a fractal function. We use the iterated function system (IFS) method to produce fractals. The IFS is only one-of-many methods available to produce fractals, but it is probably the one most commonly used in image and signal processing. This is mainly because it can lead to an automated method for fractal encoding of signals. The use of the IFS enables one to create fractal arrays with many degrees of freedom. These free parameters can then be determined so as to meet specific design parameters.

Printed fractal antennas

Abstract: One aspect of this paper is to describe the possibilities for reducing the overall size of a monopole so that they can be hidden within a system rather than protrude from it. Improved bandwidth results from the bow-tie monopole but there are instances where individual bands rather than a single band is preferable, for example for rejection of unwanted signals. One class of antenna to replace the monopole is the printed fractal antenna. Two types of fractal antennas are discussed, the Koch fractal patterns and the Sierpinski gasket which is akin to a printed bow-tie antenna. In both classes of antenna their radiation patterns, efficiency and frequency response as well as dimensions are discussed and compared. The principal application for the work described here is to provide hidden antennas on vehicles for multiband radio and television services. These include AM, FM and DAB services.

Active zone self-similarity of fractal sierpinski antenna verified using infra-red thermograms

Abstract: The surface current distribution of a Sierpinski fractal antenna shows a self-similar behaviour determined by the self-similar properties of its geometry. The application of infra-red thermography to electromagnetic near field detection allows the experimental verification of the active region scaling of a fractal antenna operating at different bands.

Self-similar surface current distribution on fractal Sierpinski antenna verified with infra-red thermograms

Abstract: Experimental verification of the fractal Sierpinski antenna surface current distribution is presented. Measured data from an infrared camera agree with numerical data showing a self-similar behavior in the current density distribution over the fractal antenna surface. This result gives a better insight on the multiband behavior of the fractal-shape antenna.

The generation of sum and difference patterns using fractal subarrays

Abstract: In this letter, we explore the potential for the application of fractal subarrays to the generation of sum and difference patterns. For the purposes of this investigation, a standard planar array is decomposed into two subarrays: one in the form of a Sierpinski carpet, and the other consisting of its complement. A methodology is then introduced for feeding the two subarrays in order to produce either a sum or a difference pattern. A particular example is considered in which directive gain plots are obtained for both the sum and difference modes of a 27×27 planar array. ©1999 John Wiley & Sons, Inc. Microwave Opt Technol Lett 22: 54–57, 1999.

A fractal based FSS with dual band characteristics

Abstract: The design of multiband frequency selective surfaces (FSS) has attracted much attention. It is clear that by arraying dual-band elements it is possible to obtain a dual band FSS. On the other hand, the multiband properties of antennas designed using fractal shapes have been previously demonstrated. It appears a natural choice to explore the feasibility of a dual-band FSS based on fractal elements. A preliminary design of a FSS based on the Sierpinski gasket dipole is presented. The FSS is designed by periodically arraying a two iteration Sierpinski dipole. A fundamental constrain of this approach is the band limitation imposed by the excitation of grating lobes. It is for this reason that the design of a dual band FSS has been addressed, instead of a more general multiband design. The performance of the Sierpinski FSS is compared with a design based on the bow-tie element. It is been shown that it is possible to exploit the multiband properties of fractal antennas to design a dual band FSS.

Iterative network models to predict the performance of Sierpinski fractal antennas and networks

Abstract: Two simple, fast numerical models to predict the input parameters of antennas and networks whose topologies are that of the Sierpinski gasket and carpet fractal shape, are introduced. These models are based on the same recursive principle used to generate fractal structures.

Experimental investigation of several novel fractal antennas-variants of the Sierpinski Gasket and introducing fractal FSS screens

Abstract: Three novel methods of improving the impedance bandwidth at each of the multiple bands of the Sierpinski Gasket are proposed. The first and second method involve compensating and applying the self-complementary principle to the Sierpinski Gasket respectively. Wave scattering from fractal frequency selective surfaces, to create additional frequency bands of considerable bandwidth, is proposed as the third method. The measured results for these antennas show significant bandwidths ranging from 18 to 80% while maintaining the self-affinity and multiband behavior of the antenna.

Fractal antenna of dendrite type

Abstract: The results of an experimental and theoretical study of the stochastic fractal antenna of the dendrite type are presented. It is shown that the fractal antenna provides the reception and transmission of microwave signals in a wide frequency band.