Fractal antenna

Fractal 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 signals 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, [ [ United States Patent: 6452553 ] ] 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 spacefilling curve is in the form of a shrunken fractal helix [ used by permission)] 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.

Log periodic antennas and fractals

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.

Fractal element antennas and superior performance

Antenna elements (as opposed to antenna arrays) made from self-similar shapes were first done by Nathan Cohen, [ [ Fractal Antenna Systems, Inc ] ] then a professor at Boston University, starting in 1988. Cohen's efforts with a variety of fractal antenna designs were first published in 1995 (thus the first scientific publication on fractal antennas), and a number of patents have been issued from the 1995 filing priority of invention (see list in references, for example). Most allusions to fractal antennas make reference to these 'fractal element antennas'.

Many fractal element antennas use the fractal structure as a virtual combination of capacitors and inductors. This makes the antenna so that it has many different resonances which can be chosen and adjusted by choosing the proper fractal design. Note that such resonances may not be related to a particular scale size of the fractal structure: the scaling of the structure does not lead to a one-to-one scaling of resonances. This complexity arises because the current on the structure has a complex arrangement caused by the inductance and self capacitance. In general, although their effective electrical length is longer, fractal element antennas are physically smaller. Fractal element antennas are shrunken compared to conventional designs, and do not need additional components. In general the fractal dimension of a fractal antenna is a poor predictor of its performance and application.

Not all fractal antennas work well for a given application, much as not all conventional antennas are suitable for a given need. Computer search methods in simulation are commonly used to identify which fractal antenna designs best meet the need.

Although the first validation of the technology was published as early as 1995 (see ref.1) recent independent studies continue to show the superiority of the fractal element technology in real-life applications, such as RFID. [ [ RFID Journal - - RFID (Radio Frequency Identification) Technology News & Features ] ]

Fractal antennas, frequency invariance, and Maxwell's equations

A different and also useful attribute of some fractal element antennas is their self-scaling aspect.In 1999, it was discovered (see reference 5) that self-similarity was one of the underlying requirements to make antennas 'invariant' (same radiation properties) at a number or range of frequencies. Previously, under Rumsey's Principle, it was believed that antennas had to be defined by angles for this to be true; the 1999 analysis, based on Maxwell's equations, showed this to be a subset of the more general set of self-similar conditions. Hence fractal antennas offer a closed-form and unique insight into a key aspect of electromagnetic phenomena. To wit: the invariance property of Maxwell's Equations.

Fractal tuned circuits, fractal inductors, fractal loads, fractal counterpoises; fractal ground planes

In addition to their use as antennas, fractals have also found application in other antenna system components including loads, counterpoises, and ground planes. Confusion by those who claim 'grain of rice'-sized fractal antennas arises, because such fractal structures serve the purpose of loads and counterpoises, rather than bona fide antennas.

Fractal inductors and fractal tuned circuits were also discovered and invented simultaneously with fractal element antennas (see reference 1 and reference 2-- patent 7256751). In the near future, fractals will have applications as inductors and tuned circuits. Fractal filters (a type of tuned circuit) are just one example where the superiority of the approach has been proven (see reference 6).

As fractals can be used as counterpoises, loads, ground planes, and filters, all parts that can be integrated with antennas, they are considered parts of some antenna "systems" and thus are discussed in the context of fractal antennas.

ee also

* Waveguide antenna.

General References

*1. Cohen, N., "Fractal Antennas", Communications Quarterly, Summer,1995, p.9.
*2. US Patents: 6104349; 6127977; 6140975; 6445352; 6452553; 6476766; 6985122; 7019695; 7126537; 7145513; 7190318;7215290; 7256751.
*3. A description of the first fractal element antenna, created in 1988, was given in reference 1, and is reproduced at: []
*4. Cohen, N.,"NEC Analysis of a Fractalized Monofilar Helix in the Axial Mode", ACES Conference Proceedings, April 1998, p.1051
*5. Hohlfeld, R., and Cohen, N., "Self-Similarity and the Geometric Requirements for Frequency Independence in Antennae", Fractals, Vol. 7, No. 1 (1999) 79-84.
*6. Hong, J., and Lancaster, M., "Microstrip Filters for RF/Microwave Applications", J. Wiley, New York (2001) p.410-411.

External links

* [ Fractal Antenna Systems website]

Wikimedia Foundation. 2010.

Игры ⚽ Поможем сделать НИР

Look at other dictionaries:

  • fractal antenna — noun An antenna that uses a fractal, self similar design in order to increase the range of frequencies which it can receive …   Wiktionary

  • Fractal analysis — is the modelling of data by fractals.It consists of methods to assign a fractal dimension and other fractal characteristics to a signal, dataset or object which may be sound, images, molecules, networks or other data.Fractal analysis is now… …   Wikipedia

  • Fractal — A fractal is generally 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, [cite book last = Mandelbrot first = B.B. title = The Fractal Geometry of… …   Wikipedia

  • Antenna (radio) — Whip antenna on car …   Wikipedia

  • Microstrip antenna — In telecommunication, there are several types of microstrip antennas (also known as printed antennas) the most common of which is the microstrip patch antenna or patch antenna. A patch antenna is a narrowband, wide beam antenna fabricated by… …   Wikipedia

  • List of fractal topics — This is a list of fractal topics, by Wikipedia page, See also list of dynamical systems and differential equations topics.*1/f noise *Apollonian gasket *Attractor *Box counting dimension *Cantor distribution *Cantor dust *Cantor function *Cantor… …   Wikipedia

  • Parabolic antenna — A parabolic satellite communications antenna at Erdfunkstelle Raisting, the biggest facility for satellite communication in the world, in Raisting, Bavaria, Germany. It has a Cassegrain type feed. A parabolic antenna is an antenna that uses a… …   Wikipedia

  • Dipole antenna — A schematic of a half wave dipole antenna connected to an unbalanced coaxial cable. Better practice is to connect the balanced dipole to the unbalanced line with a balun. A dipole antenna is a radio antenna that can be made of a simple wire, with …   Wikipedia

  • Whip antenna — on car A whip antenna is an antenna consisting of a single straight flexible wire or rod, often mounted above some type of conducting surface called a ground plane.[1] The bottom end of the whip is connected to the radio receiver or transmitter.… …   Wikipedia

  • Discone antenna — Mounted discone antenna designed for VHF and UHF coverage …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”