Showing papers on "Fractal antenna published in 2001"

Hilbert curve fractal antenna: A small resonant antenna for VHF/UHF applications

Abstract: The usefulness of fractal Hilbert curves in antenna geometry is explored here for the first time. Apart from being simple and self-similar, these curves have the additional property of approximately filling a plane. These properties are exploited in realizing a “small” resonant antenna. This approach has resulted in an antenna size smaller than λ/10 and still resonant, with performance comparable to a dipole whose resonant length is close to λ/2. Numerical predictions of the input impedance of the antenna have been compared with experiments. The effect of additional fractal iterations on the reduction of the resonant frequency has been studied. The radiation characteristics of the antenna at the resonant frequencies provided show that this is very similar to the dipole characteristics. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 29: 215–219, 2001.

Generalized Sierpinski fractal multiband antenna

Abstract: A new set of fractal multiband antennas called mod-p Sierpinski gaskets is presented. Mod-p Sierpinski fractal antennas derive from the Pascal triangle and present a log-periodic behavior, which is a consequence of their self-similarity properties. Mod-p Sierpinski fractal antennas constitute a generalization of the classical Sierpinski antenna.

Small and high-directivity bow-tie patch antenna based on the Sierpinski fractal

Abstract: The unique geometrical properties of fractals have been proven to be useful to design advanced antennas. Enhanced performance in terms of size, gain, or multifrequency behavior is observed in fractal-shaped antennas. Here, a small and high-directivity antenna based on the Sierpinski fractal is presented. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 31: 239–241, 2001.

Genetically engineered multiband fractal antennas

Abstract: Fractal antenna engineering concepts have been successfully combined with genetic algorithms to develop a powerful design optimisation tool. The genetic optimisation approach developed can simultaneously optimise the geometry of a fractal antenna, locations of loads, component values of loads, and projected length of the fractal antenna. The results suggest that a 30 to 55% size reduction can be achieved by optimising the fractalisation of a given antenna. The knowledge gained from this study is directly applicable to the design of miniature multiband fractal antennas.

Miniaturized conformal wideband fractal antennas on high dielectric substrates and chiral layers

Abstract: A class of antennas that comprise an electrically conductive fractal pattern disposed on a dielectric substrate and are capable of construction in a size measured in centimeters as compared to previous antennas of the same class that measured in meters. One antenna style has a ground plane that is perpendicular to the substrate and another style has a ground plane that is parallel to the substrate. The substrate has a dielectric constant of in the range of about 10 to 600 or more and may be a ferroelectric, such as barium strontium titanate. A bias voltage applied across the substrate can tune the antenna for operation in a particular frequency range. The antenna can be made especially wideband by placing an absorbing material behind the substrate. The fractal pattern may be any fractal pattern, such as Hilbert curve, Koch curve, Sierpinski gasket and Sierpinski carpet. One style of the antenna uses a fractal pattern that has a plurality of segments arranged in a first configuration and a switch disposed to alter the first configuration to one or more other configurations. The antenna elements may also be arranged in a phased array.

Resonant frequency of Hilbert curve fractal antennas

Abstract: An approximate formulation for the resonant frequency of a dipole Hilbert curve fractal antenna (HCFA) is derived here. These can be used as small resonant antennas, useful in VHF/UHF communication. The formulas presented here can be appropriately inverted to obtain the design equations for the antenna, for a given resonant frequency.

Design of reconfigurable fractal antennas and RF-MEMS for space-based systems

Abstract: In this paper, design concepts of reconfigurable and electronically steered antennas based on a new fractal antenna and RF-MEMS devices are presented. As modern telecommunications extend towards higher frequencies, the advantages of employing RF-MEMS switches, phase shifters, and miniaturized fractal antennas become more significant. The input characteristics of the Hilbert curve fractal antenna can be made frequency agile by incorporating RF switches along its length. In addition, due to the large number of connected segments in this antenna geometry, reconfigurable radiation characteristics can be obtained by adding just a few additional line segments to interconnect these through semiconductor or RF-MEMS switches. The beam peak direction can be shifted by 63° and the beam width can be changed by up to 25° by this approach. An electronically steered antenna with micromachined phase shifters using tunable ferroelectric barium strontium titanate thin film is also discussed. These MEMS-based antenna systems find applications in communications satellites and electronically scanned arrays for space-based radars.

Hilbert curve fractal antennas with reconfigurable characteristics

Abstract: Fractal Hilbert curve is one of the most recent geometries to be studied for antennas. This geometry results in an antenna with low resonant frequency compared to other configurations. The antenna consists of line segments arranged in a predictable fractal order, thus enabling easy generation and reproducible results compared to an arbitrary shrinkage of antenna size. This can be modeled using wire segments. An addition of few more interconnecting segments to the geometry is found to result in significant changes in its radiation pattern. With RF switches within these few selected additional segments and the necessary control units, radiation pattern of the antenna can be made adaptively reconfigurable. Similarly, switches connected in series along the length of the antenna result in frequency tuning characteristics.

The Koch island fractal microstrip patch antenna

Abstract: The Koch island fractal patch antenna is introduced in order to reduce the antenna size. By the space-filling property of fractal geometry, this antenna reveals lower resonant frequency than that of a normal square patch antenna. Based on experimental results, it is found that as iteration and iteration factor increases, the resonant frequency of this patch antenna decreases, while maintaining a radiation pattern similar to that of normal square patch.

Fractal FSS: various self-similar geometries used for dual-band and dual-polarized FSS

Abstract: In our attempt to design a frequency selective surface (FSS) that is resonant at two distinct bands, dual-polarized, and has a simple planar design, several self-similar elements based on fractal geometry have been investigated. In this paper these various geometries are presented along with their characteristics.

Modified Sierpinski gasket patch antenna for multiband applications

Abstract: In this paper we present an investigation of the Sierpinski gasket patch antenna and propose a novel technique to improve the multiband behavior of this patch antenna.

Shorted fractal Sierpinski monopole antenna

Abstract: The novel configuration of a shorted fractal Sierpinski gasket antenna is proposed. The new configuration is similar to the inverted L antenna and the shorted loop monopole. Using only half the Sierpinski gasket structure, the symmetrical side is folded over to be parallel to the ground plane. While the 50/spl Omega/ feed remains at the apex, a shorting pin is placed at the far end of the gasket. A planar configuration of this design is also demonstrated.

Analysis of microstrip fractal patch antenna for multi-band communication

Abstract: The square microstrip fractal patch antenna in a Sierpinski carpet and the effects of its elements are analysed. The calculated results show that the multi-band frequency operation of the proposed antenna results from the driven element and not from the parasitic fractal elements.

Genetically engineered dual-band fractal antennas

Abstract: Fractal antenna engineering concepts have been successfully combined with genetic algorithms to develop a powerful design optimization tool. The genetic optimization approach developed can simultaneously optimize the geometry of a fractal antenna, locations of loads, component values of loads, and the projected length of the fractal antenna. The results suggest that a 30-55% size reduction can be achieved by optimizing the fractalization and loading of a given antenna. The knowledge gained as a result of this study is directly applicable to the design of miniature fractal antennas.

Fracton vibration modes in the Sierpinski microstrip patch antenna

Abstract: The localization properties of mass fractal patches are described in this paper for the Sierpinski patch antenna. The localization of the electrical current results in a patch antenna that has two localized modes with a frequency ratio of two and a directivity of 12.2 dB and 14.7 dB respectively.

Fractal antenna research at University of Birmingham

Abstract: The use of fractal geometry in electromagnetics has been a recent topic of interest. In antenna applications, the Minkowski loop, the Koch curve monopole, the Koch island patch, the Sierpinski carpet and the Sierpinski gasket have been reported. In particular, the fractal Sierpinski gasket monopole antenna which demonstrates a log periodic resonant property. Although the fractal structure from these mathematical functions could provide attractive multiband performance, it has become clear that such geometry requires further modification to enhance their application. However, perturbation effectively varies the structural properties, and hence electrical properties. In this paper, we present two recent developments of these fractal monopole antennas at the University of Birmingham. The first development describes the multiband behaviour of a perturbed fractal Sierpinski gasket and a perturbed Parany monopole antenna. Both antennas have a periodic ratio of 0.75 and 0.775 respectively. The first antenna demonstrates four operating bands while the latter design involves eight bands. Two methods are presented to demonstrate improvements to the inherently poor input impedance match of these antennas with a 50 /spl Omega/ port. These improved feeding methods will allow further flexibility to the application of these multiband antennas. The second development looks into an alternative multi-level structure antenna which may provide bandwidth improvements without sacrificing antenna performance. The design consists of a set of self similar circular rings, as an alternative to the triangular fractal Sierpinski gasket monopole antenna. A comparison of both antennas with scale factor of 0.5 is described.

The fractal loop antenna: a comparison of fractal and non-fractal geometries

Abstract: Fractal antennas have been shown to demonstrate repetitive multi-band or log-periodic behavior that has been attributed to the self-similar scale factor of the antenna's geometry. Additionally, fractal loop antennas have been shown to demonstrate improved impedance and SWR performance in a reduced physical area when compared to non-fractal Euclidean geometries. The purpose of this paper is to numerically model fractal and non-fractal loop antennas occupying the same physical area in an effort to understand whether the fractal geometry of the loop is the significant parameter in determining the loop performance. It is demonstrated through numerical modeling that the fractal geometry is not the critical factor in determining the loop performance and in fact, non-fractal geometries offer similar and in some cases, improved performance over their fractal counterparts.

Shorted fractal Sierpinski monopole antenna

Abstract: A novel configuration of a shorted fractal Sierpinski gasket antenna is proposed. Using only half the structure of a conventional Sierpinski gasket, the antenna is folded over to be parallel to the ground plane, to form an element that is, in some ways, similar to the inverted L antenna. A shorting pin is then placed at the far end of the antenna. A quasi log periodic resonance behaviour is observed.

An improved microstrip Sierpinski carpet antenna

Abstract: The boundary integral method coupled with the segmentation method have been used for the first time to analyzed Sierpinski carpet antennas of different order. The close agreement between calculated and measured results for resonant frequency and input return loss indicates that this technique can predict the impedance characteristic accurately. A novel double layered stacked microstrip Sierpinski carpet fractal antenna using a photonic bandgap structure is also presented. This proposed antenna has improved the impedance bandwidth five fold compared to an ordinary microstrip fractal antenna and its radiation pattern is improved due to the removal of unwanted radiation caused by the surface wave.

Analysis and bandwidth enhancement of Sierpinski carpet antenna

Abstract: The boundary integral method coupled with the segmentation method have been used for the first time to analyze Sierpinski carpet antennas of different orders. As is evident from the close agreement between calculated and measured results for the resonant frequency and input return loss, this technique is found to predict the impedance characteristic accurately. A novel stacked microstrip Sierpinski carpet fractal antenna using a photonic bandgap structure is also presented. Compared to an ordinary microstrip fractal antenna, which has a maximum bandwidth of 2%, the proposed antenna has a higher input impedance bandwidth of about 9%. The radiation patterns of the proposed antenna are improved due to the removal of unwanted radiation caused by the surface wave. The experimental measurement results of the proposed antenna are presented in this paper. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 31: 13–18, 2001.

Analysis of a microstrip antenna with fractal multilayer substrate using iterative method

Abstract: A microstrip antenna with fractal multilayer substrates is studied by using an iterative method based on the concept of waves. A two-dimensional fast Fourier transformation algorithm is introduced to simplify calculations and accelerate the convergence with reduced central processing unit time. Good agreements are obtained with already published results on fractal antenna. © 2001 John Wiley & Sons, Inc. Int J RF and Microwave CAE 11: 212–218, 2001.

UHF fractal antennas

Abstract: The use of fractal antenna techniques to reduce the size of a UHF linear dipole is investigated and discussed. Fractal designs are derived using an empirical method and a genetic algorithm based method. While both achieve size reduction, the latter design shows the most promise from a size reduction and design methodology standpoint, since simulation is inherent in the design process and discretely loaded designs are possible.

Scaling property of the Koch fractal dipole

Abstract: The increased interest in fractal antennas is due to their possible application in multi-band wireless communication devices. The fractal antenna is formed by applying a generator shape repetitively at a constant scale factor and results in an antenna with log-periodic characteristics. By utilizing the selfsimilar nature of the fractal shape, one can develop some fast approximation techniques.

Design of reconfigurable fractal antennas and RF-MEMS for spaced-based communication systems

Abstract: In this paper, design concepts of reconfigurable and electronically steered antennas based on a new fractal antenna and FR-MEMS devices are presented. The input characteristics of the Hilbert curve fractal antenna can be made frequency agile by incorporating RF-MEMS switches along its length. In addition, due to the large number of connected segments in this antenna geometry, reconfigurable radiation characteristics can be obtained by adding just few additional line segments to interconnect these through semiconductor or RF-MEMS switches. The beam peak direction can be shifted by 63 degree(s) and the beam width can be changed by up to 25 degree(s) by this approach. An electronically steered antenna with micromachined phase shifters using tunable ferroelectric barium strontium titanate thin film is also discussed. These MEMS based antenna systems find applications in communications satellites and electronically scanned arrays for space-based radars.

An efficient recursive procedure for calculating the driving point impedance of linear and planar fractal arrays

Abstract: A methodology is introduced in this paper for exploiting the self-similarity in the geometrical structure of fractal arrays to develop fast algorithms for calculating the impedance matrix and driving point impedance of such arrays. Two specific examples of fractal arrays are considered, namely, triadic Cantor linear arrays and Sierpinski carpet planar arrays.

Circuit board has electrically conducting structure in at least one defined area forming planar antenna terminated by at least one resistance in an at least approximately reflection-free manner

Abstract: The circuit board (17) has at least one insulating layer with electrically conducting structures on at least one side, whereby the electrically conducting structure in at least one defined area of the board forms a planar antenna (20) that is terminated by at least one resistance (22) in an at least approximately reflection-free manner. The antenna is in the form of a slot or fractal antenna.

Experiences on multiband fractal antennas

Abstract: This paper presents the development of a multiband fractal antenna based on the Sierpinski triangle. By changing the structure, upper bands may be selected over a number of multiple frequencies. This property is based on Pascal triangle properties. The paper also develops an explanation of why fractal antennas have constant radiation properties at multiband frequencies. Finally, some impedance and radiation measurements are presented.

A modification of the small loop approximation for fractal and bent wire loop antennas

Abstract: The small loop approximation has been previously applied to the fractal loop and it was concluded that fractal loop antennas do not obey the generalizations of the small loop approximation because of their fractal geometry. In this work, the small loop approximation and its applicability to fractal and other bent wire loop antennas is re-evaluated. It is demonstrated that the small loop approximation for the radiation resistance of a small loop is valid for loops with fractal or bent wire geometries, when these loops meet all of the small loop criteria. In applying the small loop approximation criteria to these loop antennas, a modification of the small loop area limit is presented that allows an approximate determination of the frequency at which fractal and other bent wire loop antennas can be considered electrically small.

Improving the performance of the method of moments for the analysis of fractal antennas

Abstract: Fractal antennas present some particular properties as self-similarity, miniaturization and localized vibration modes that result in high directive microstrip patch antennas with multiband behavior. These fractal properties will be used here to simplify the numerical analysis of fractal antennas with the Method of Moments. The adaptive meshing of the geometry and a recursive procedure that makes use of the concept of macro basis functions will be presented as some possibilities of improving the computational requirements in the analysis of fractal antennas. The recursive procedure applied in the analysis of a Sierpinski patch antenna discretized in 1700 unknowns gives a reduction factor of six in memory and nine in CPU time respect to the Method of Moments traditional solution.

RF MEMS and reconfigurable conformal fractal antennas

Abstract: Antennas with the capability to adaptively change any of its characteristics are called reconfigurable antennas. Although originally conceived for satellite broadcast antenna applications, the same philosophy is applicable top many telecommunication antennas. With the large increase in modem communication equipment, reliance on higher frequencies is bound to increase. RF-MEMS based systems and reconfigurable antennas using these would be increasingly useful in such cases. In this paper, two fractal based antennas are introduced, along with concepts to incorporate reconfigurability into these. It is expected that such antenna systems may replace most of the existing antenna systems in the near future.