Faculty of Physics - University of Bucharest

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Conference: Bucharest University Faculty of Physics 2001 Meeting

Section: Atomic and Molecular Physics; Astrophysics

Title:

Fractal Antennae - Invited Lecture

Authors:

Mircea V. Rusu

Affiliation:

Faculty of Physics, University of Bucharest

E-mail

Keywords:

Abstract:

Since their first description in the 1970s and used in description of a variety of natural phenomena by physicist, chemists, etc., the repeating geometric figures called fractals have been embraced by math fans, graphic artists, and computer scientists. Fractals are geometric shapes whose edges repeat over a variety of scale sizes so the shape looks the same viewed from a distance or close-up. The fractal design of antennas and arrays results from the blend of two apparently disjoint disciplines: electromagnetic theory and geometry. From the early spiral and log periodic antennas developed in the early sixties, and from the works of Benoit Mandelbrot on fractal geometry, the fractal design of antennas appears as a natural way to explore for a multifrequency operation and for an antenna size reduction. Fractal antenna development has a natural evolution from the early work on antennae. In the 40s. L.J.Chu and H.Wheeler establish a fundamental limit on the performance of small antennas. In the 60s. researchers at the University of Illinois, University of California, and Ohio State University introduce the concept of frequency independent antennas. The self-scaling concept gives place to the log periodic dipole array and to the spiral antennas. In 70s. B. Mandelbrot coins the term Fractal. Such a name is used to describe a family of geometrical objects that defy the traditional rules of the Euclidean geometry. In 80s. D.Jaggard et al. coins the term Fractal Electrodynamics. The interaction of fractal bodies and electromagnetic waves are investigated and some relationships between common fractal properties and the scattered electromagnetic waves are established. In 90s. the first reported fractal multiband antennas are introduced by researchers the Universitat Politecnica de Catalunya from the University of Boston. Between 1996 1998 the first reported experimental results on fractal multiband antennas are published by the Electromagnetics and Photonics Engineering research team from the Universitat Politecnica de Catalunya. In 1998 the Koch monopole becomes the first reported fractal small antenna that improves the features of some classical antennas in terms of bandwidth, resonance frequency and radiation resistance. In the same year the Fractal Team from the Electromagnetics and Photonics Engineering group (UPC), in cooperation with FractusTM the Fractal AntennasTM company from the Sistemas Radiantes F.Moyano S.A. group, develop the first commercial multiband fractal shape antennas for GSM DCS cellular phone systems. Some of the design was already patented. Researches on fractal systems were carried out at the Physics Faculty from Bucharest University since 80s. Our investigations started with the problem of electromagnetic waves scattering on fractal surfaces and structures, and ended in the 1999 by studying and designing fractal antennae for cars in collaborations with the Opel Factories from Germany. The systems were subject to a patent pending to Opel. The lecture will be focused on the main aspects of fractal electrodynamics related to the antennae design, and will describe some of the results obtained in our department.