Showing papers on "Fractal antenna published in 2000"
TL;DR: In this article, the behavior of the small fractal Koch monopole is numerically and experimentally analyzed, and it is shown that as the number of iterations on the small Koch monopoles are increased, the Q of the antenna approaches the fundamental limit for small antennas.
Abstract: Fractal objects have some unique geometrical properties. One of them is the possibility to enclose in a finite area an infinitely long curve. The resulting curve is highly convoluted being nowhere differentiable. One such curve is the Koch curve. In this paper, the behavior the Koch monopole is numerically and experimentally analyzed. The results show that as the number of iterations on the small fractal Koch monopole are increased, the Q of the antenna approaches the fundamental limit for small antennas.
457 citations
TL;DR: In this paper, a simple model that explains the behavior of the Sierpinski fractal antenna is presented, and the model is applied to predict the behavior when the flare angle is modified and its validity is assessed by comparing its predictions with measured data.
Abstract: A simple model that explains the behavior of the Sierpinski fractal antenna is presented. This model shows that the multiband behavior of the Sierpinski fractal antenna is a consequence of its fractal nature. The model is applied to predict the behavior of the Sierpinski fractal antenna when the flare angle is modified and its validity is assessed by comparing its predictions with measured data.
143 citations
TL;DR: In this paper, a microstrip patch antenna with a fractal boundary condition is proposed, where the fractal characteristic of the perimeter produces localised modes, and this property is utilized in the design of the microstrip antenna with measured directivity of 12.7 dB.
Abstract: A novel patch antenna with a fractal boundary condition is proposed. Experimental and numerical results corroborate the fact that the fractal characteristic of the perimeter produces localised modes. This property is utilised in the design of a microstrip patch antenna with a measured directivity of 12.7 dB.
69 citations
TL;DR: In this article, a technique for the design of multiband frequency selective surfaces (FSSs) that is based on the use of fractal screen elements is proposed, where the frequency response of both the TE and TM modes are exactly the same, owing to the symmetry in the tree-like fractal structure of the screen elements.
Abstract: A technique is proposed for the design of multiband frequency selective surfaces (FSSs) that is based on the use of fractal screen elements. The authors demonstrate the design methodology by exploiting the self-similarity of the crossbar fractal to implement a tri-band FSS. Another benefit of this design approach, in addition to its multiband performance, is that the frequency response of both the TE and TM modes are exactly the same, owing to the symmetry in the tree-like fractal structure of the screen elements. Dielectric loading effects have been considered for practical implementation of designs with coverage exceeding two bands. Finally, it is noted that the locations of the individual bands can be controlled by the scaling or similarity factor used in the construction of the fractal screen elements.
65 citations
TL;DR: In this paper, a square microstrip fractal patch antenna in a Sierpinski carpet is proposed for three-band operation and measured results indicate that the return loss is better than 10 dB and the gain is greater than 7 dB in each band.
Abstract: A novel square microstrip fractal patch antenna in a Sierpinski carpet is proposed for three-band operation. Measured results indicate that the return loss is better than 10 dB and that the gain is greater than 7 dB in each band. This antenna is an attractive candidate for wireless, satellite and mobile communication applications.
60 citations
16 Jul 2000
TL;DR: In this paper, a compilation of simulations of several simple fractal geometries that either miniaturize or improve the input match of element antennas (including fractal loops, fractal dipoles, and multiband fractal antennas) are presented.
Abstract: Fractal geometries have been used in science to mathematically define intriguing features observed in nature, from describing the formation of clouds to coastlines to tree bark. It expands the horizon of possible geometries, some of which may lead to enhanced performances in antenna designs. Fractal geometries have been studied as array elements and distributions, with the goal of finding miniaturized and efficient radiators. A compilation of simulations of several simple fractal geometries that either miniaturize or improve the input match of element antennas (including fractal loops, fractal dipoles, and multiband fractal antennas) are presented.
48 citations
01 Jan 2000
TL;DR: This chapter provides 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.
Abstract: One of the most fruitful areas of fractal electrodynamics research to date concerns the application of fractal geometry to antenna engineering. In this chapter 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. Several important properties of fractal arrays will be presented and discussed in this chapter. These include the frequency-independent multiband characteristics of fractal arrays, schemes for realizing low sidelobe designs, systematic approaches to thinning, and the ability to develop rapid beamforming algorithms by exploiting the recursive nature of fractals.
36 citations
TL;DR: In this paper, the effect of channel tortuosity and branching is investigated by adopting a suitable numerical technique, where the discharge channel has been regarded as a fractal antenna whose associated EM field has been evaluated by superimposing the contribution of the single line radiators composing the whole channel.
Abstract: Usually the electric and magnetic fields associated with lightning have been computed by assuming the lightning current to be contained in a straight vertical channel of negligible cross section above a flat perfectly conducting plane. Such a model, which does not take into account that real lightning is characterized by tortuosity and branching, is not able to justify the fine structure of the fields radiated by lightning discharges whose time-domain behavior exhibits a jagged shape with remarkable spectral content in several bands of practical interest. In this work the effect of channel tortuosity and branching is investigated by adopting a suitable numerical technique. The discharge channel has been regarded as a fractal antenna whose associated EM field has been evaluated by superimposing the contribution of the single line radiators composing the whole channel. Such a field has been compared with that generated by a simple dipole antenna in order to study the influence of the fractal nature of the channel on the generated EM fields. The relationship between the fractal dimension of the discharge channel and the fractal dimension of the generated time domain EM fields has been considered and the influence played on such a relationship by the distance between EM source and observation point has also been studied by analyzing the fields evaluated at far and close distances.
35 citations
16 Jul 2000
TL;DR: In this paper, the authors show that a patch antenna with fractal boundary exhibits localized modes at a frequencies above the fundamental mode, and these modes can have broadside directive patterns, which is similar to the one described in this paper.
Abstract: The article shows that a patch antenna with fractal boundary exhibits, at a frequencies above the fundamental mode, localized modes. These modes can have broadside directive patterns. As an example of this phenomenon experimental data on the Koch island patch antenna is presented.
32 citations
16 Jul 2000
TL;DR: In this paper, a technique for the design of multiband frequency selective surfaces (FSSs) that is based on the use of fractal screen elements was proposed, and demonstrated by exploiting the self-similarity of the crossbar fractal to implement a tri-band FSS.
Abstract: We propose a technique for the design of multiband frequency selective surfaces (FSSs) that is based on the use of fractal screen elements. We demonstrate the design methodology by exploiting the self-similarity of the crossbar fractal to implement a tri-band FSS. Another benefit of this design approach, in addition to its multiband performance, is that the frequency response of both the TE and TM modes are exactly the same, owing to the symmetry in the tree-like fractal structure of the screen elements. Dielectric loading effects have been considered for practical implementation of designs with coverage exceeding two bands.
23 citations
16 Jul 2000
TL;DR: In this article, the multiband behavior of the Sierpinski patch antenna is described, and a new technique to improve the multi-band behavior from the point of view of the radiation patterns is introduced.
Abstract: The multiband behavior of the Sierpinski patch antenna is described, and a new technique to improve the multiband behavior from the point of view of the radiation patterns is introduced. The technique suppresses the effects of the high order modes and a patch antenna with similar radiation patterns can be designed. Once the high order mode has been suppressed for the second band, the next step is to try eliminate it for the third and fourth band breaking the appropriate junctions.
16 Jul 2000
TL;DR: In this article, a new top-loaded reduced-sized dual-band (1.9 GHz and 3.5 GHz) monopole antenna for wireless communications is presented, which provides better than -15 dB input return loss and keeps the same radiation pattern over both bands.
Abstract: A new top-loaded reduced-sized dual-band (1.9 GHz and 3.5 GHz) monopole antenna for wireless communications is presented. The antenna provides better than -15 dB input return loss and keeps the same radiation pattern over both bands. In addition, a low-profile performance is achieved.
16 Jul 2000
TL;DR: The generation and behavior of the fractal Koch array factor from a Kaiser window generator is studied and it is shown that moderate quantization keeps the same interesting similarity properties at several bands.
Abstract: The generation and behavior of the fractal Koch array factor from a Kaiser window generator is studied. The main advantage of using Kaiser windows is that pattern parameters become much more flexible through altering the Kaiser window. The mainlobe width, current distribution, side-lobe ratio are now adjustable. Different reduced array structures can be obtained by using different threshold levels. Higher threshold values result in a highly reduced number of elements but they may highly distort the pattern and, hence, the multiband behavior. Finally, we study the effect of quantization of the feeding values. Quantization is necessary for implementation and simplification purposes. Several configurations of current distributions with the corresponding patterns are illustrated for different quantization levels. It is shown that moderate quantization keeps the same interesting similarity properties at several bands.
TL;DR: In this article, a new fractal geometry of the cross antenna, which belongs to the traveling-wave antenna class and follows the contour of a cross, is presented, and their performance is examined by measurements.
Abstract: A new fractal geometry of the cross antenna, which belongs to the traveling-wave antenna class and follows the contour of a cross, is presented. In the conventional type of traveling-wave antenna, the total length of the radiating conductor increases as the order of fractal expansion increases, but this increase of the length of the current path degrades the performance of the antenna. To reduce the antenna performance degradation, a hybrid fractal antenna is presented, which divides the entire fractal structure into some smaller ones, and connects each smaller fractal group with a power divider circuit. The secondarily, thirdly, and fourthly expanded hybrid fractal cross antennas are fabricated, and their performances are examined by measurements. The influences of the fractal order on the antenna performance are examined. © 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 25: 429–435, 2000.
TL;DR: In this paper, the benefits of using fractal elements in linear phased arrays to achieve denser packing while minimizing mutual coupling is discussed, and two methods for utilizing fractal in arrays are presented: one method is fractal arrays, which arrange elements in fractal patterns.
Abstract: A common goal for array antennas has been to pack the elements tighter for lower scan angles while fighting mutual coupling. The emergence of wireless networks as a rapidly expanding market has brought about a need for very small and efficient phased array antennas. An optimal design would incorporate tightly packed elements for efficient directed transmissions that radiate effectively without significant mutual coupling. This paper presents arrays for a wireless LAN configuration, designed at 2 GHz for operation at the PCS band, that scan lower angles more efficiently than conventional designs. We show the benefits of using fractal elements in linear phased arrays to achieve denser packing while minimizing mutual coupling. Previous work has shown that fractal geometries are an effective means of miniaturizing antennas. The smaller elements can work in an array in two ways: the first is to increase the gap size between the elements, thus reducing the coupling between them; the second is to allow more elements into a fixed length array for broader scan angles. Also, there are two methods for utilizing fractal in arrays. One method is fractal arrays, which arrange elements in fractal patterns. The other method, analyzed here uses fractals as elements. Linear arrays of fractal square loop elements are analyzed using a method of moments computer code developed at UCLA.
16 Jul 2000
TL;DR: In this paper, the authors used fractal geometries to miniaturize the elements of the arrays to reduce the amount of coupling by increasing the spacing between the elements, thus enhancing the array performance.
Abstract: Effective array design should take into account mutual coupling. This becomes even more of a troublesome area as arrays are packed tighter to increase the scan angles in phased array systems. One attempt to control mutual coupling that is utilized here is to miniaturize the elements of the arrays. The smaller elements decrease the amount of coupling by increasing the spacing between the elements, thus enhancing the array performance. To miniaturize the elements, fractal geometries are used. Fractal geometries have also been used in arrays by defining the distribution of elements.
21 Jun 2000
TL;DR: The paper presents the experimental result on the transmission and backscatter characteristics of a fractal FSS screen, and uses fractal patterns to result in such band pass characteristics.
Abstract: On many situations the reduction of radar cross section (RCS) is of continued strategic interest, especially with aircraft and missiles. Once the overall RCS of the vehicle is reduced, the reflections from the antennas can dominate. The commonly known approaches to RCS reduction may not be applicable for antennas, and hence special techniques are followed. These include configuring the antennas completely conformal, and using band pass frequency selective surfaces. The use fractal patterns have shown to result in such band pass characteristics. The overall RCS of a typical target body is experimentally found to be reduced when these screens are used. The paper presents the experimental result on the transmission and backscatter characteristics of a fractal FSS screen.
22 Feb 2000
TL;DR: In this paper, a technique is introduced for the simplification and size reduction of the Koch array, which can result in an array current distribution having lower side lobes, with a reduced array size after setting a threshold beyond which the elements are eliminated.
Abstract: Fractal arrays are known for their self-similar performance in multi-band operation. A large number of elements in the array is a source of inconvenience in the realization procedure. In this paper, a technique is introduced for the simplification and size reduction of the Koch array. The fractal array factors presented keep the same shape at several bands because they are constructed from self-similar curves. A Kaiser window as a generating pulse function is proposed for the design of Koch-array factors. Kaiser windows are characterized by having the lowest side lobes of all windows in the transformed domain. Applying such a technique would result in an array current distribution having lower side lobes, with a reduced array size after setting a threshold beyond which the elements are eliminated. The resulting reduced array is then quantised for implementation purposes. This paper also compares the performance of reduced Koch arrays for multiband operation with their derivative Koch arrays.
06 Nov 2000
TL;DR: Fractal geometries can be utilized to design miniaturized resonant loop antennas that can increase the flexibility of the design of planar phased arrays as mentioned in this paper, leading to a more optimal synthesis of phased arrays that can be incorporated into portable wireless devices.
Abstract: Fractal geometries can be utilized to design miniaturized resonant loop antennas that can increase the flexibility of the design of planar phased arrays. Smaller fractal loop elements lead to a more optimal synthesis of phased arrays that can be incorporated into portable wireless devices. Their planar structures also allows for easy fabrication.
Patent•
27 Jan 2000
TL;DR: In this article, a microstrip antenna with fractal or prefractal perimeter is described, where the antenna is formed by a flat surface made of conductive or superconductive material.
Abstract: Microstrip antenna with fractal or prefractal perimeter.This invention relates to a microstrip antenna (1) whose perimeter (5) is fractal or prefractal. The antenna is formed by a flat surface made of conductive or superconductive material (2) whose perimeter is fractal or prefractal, placed in a parallel manner on a conductive or superconductive plane (3). Between both planes, there are one or several layers of dielectric material (4). The activation method of the antenna can be any of the conventional methods for this type of antenna, for example, by coaxial probe, slot, or electromagnetic coupling. These antennas, which are activated at certain frequencies greater than the frequency of the first resonance, have radiation diagrams whose maximum value is in the direction that is perpendicular to the plane that contains the antenna. At these frequencies, the directivity of the antenna is greater than that obtained at the frequency of the first resonance.
12 Sep 2000
TL;DR: In this paper, the magnetic field component of a symmetric spherical emitter and current distribution on a surface is described. And the application of a fractional calculation for the mathematical model generation is justified.
Abstract: Results of mathematical simulation of a spherical fractal emitter are presented. The application of a fractional calculation for the mathematical model generation is justified. The /spl alpha/-characteristic of the magnetic field component of a symmetric spherical emitter and current distribution on a surface is obtained. The properties of a spherical fractal emitter are defined. The outputs are confirmed by matching the obtained formulas and graphs with known data.
11 Sep 2000
TL;DR: Input characteristics of printed fractal antenna of dendrite type were simulated using the method of equivalent R-L-C circuits, whose topology is corresponds to the topology of the antenna.
Abstract: Input characteristics of printed fractal antenna of dendrite type were simulated using the method of equivalent R-L-C circuits, whose topology is corresponds to the topology of the antenna. The results of simulation demonstrate good agreement with experimental data.
11 Sep 2000
TL;DR: In this paper, the features of radiation fields of spherical emitter with fractal distribution of surface currents have been investigated and the influence of current fractal degree on the direction of radiation maximums and the value of directivity has been defined.
Abstract: The features of radiation fields of spherical emitter with fractal distribution of surface currents, have been investigated The influence of current fractal degree on the direction of radiation maximums and the value of directivity has been defined
21 Jun 2000
TL;DR: In this article, a fractal antenna with dielectric substrates and fractal patterns is presented. But the fractal antennas with multi-band and multi-functional capabilities have been very actively studied in the recent years.
Abstract: The fractal antennas with multi-band and multi-functional capabilities have been very actively studied in the recent years. In contrast, the fractal antenna presented here combines properties of the dielectric substrates with the well-known characteristics of fractal patterns, to result in a wideband conformal antenna. The input characteristics of the antenna is experimentally found to be better than -10 dB for a very band of frequencies from MHz to few GHz band. Another important characteristics of the fractal antennas introduced her is the possibility of making a reconfigurable antenna with this approach. Preliminary simulation results for a fractal reconfigurable antenna are presented here.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.