Universitat Politecnica De Catalunya (UPC)
Electromagnetics And Photonics Engineering Group (EEF), C/ Jordi Girona 1-3
08034 Barcelona, Spain
The increasing range of wireless telecommunication services and related applications is driving the attention to the design of multifrequency (multiservice) and miniature antennas. Through such a kind of antennas, telecom operators and equipment manufacturers can reduce the visual impact of their cellular networks and integrate the several services into a single, compact system respectively.
The design of multiband and small antennas has been for decades a challenging problem in the field of electromagnetics engineering. Basically, there is a natural, physical trade-off between the antenna size and the operating wavelength that severely constraints the antenna behavior. The overall size of the antenna is directly linked to the wavelength such that either a multiwavelength operation and a size reduction becomes difficult. Although several approaches have been widely proposed in the literature, all of them have been based on particular solutions for specific applications.
The development of the first multiband fractal-shaped antennas at the Universitat Politècnica de Catalunya back in 1994 opened a wide-scope of new chances in the development of multifrequency and small antennas. Relying on the particular geometrical properties of fractals, such a novel technology defies the traditional constraints of classical antennas. Fractals are self-similar objects which roughly means that they are composed only by multiple copies of themselves at several scales. The early works of the EEF team from the UPC demonstrated that such particular features become imprinted on the electromagnetic behavior of the antenna when it is fractally shaped. Similarly, it is suspected that another significant property of fractals, their fractional dimension, plays a key role in the enhanced performance of small fractal antennas. Again, the same team from the UPC was the first to show in 1997 that by fractally shaping an antenna a significant size reduction could be achieved while increasing, at the same time, the radiation resistance, operating wavelength and bandwidth of the antenna. Owing to the 'pathological' geometrical features of fractals, one might even suspect that the classical fundamental limits on small antennas established by H.Wheeler and L.J.Chu in the middle 40's might not apply to fractal shaped antennas, becoming a most interesting and challenging scientific and engineering research topic.
Beyond the theory of fractal-shaped antennas, this technology has found applications in real telecommunication environments. In 1997 the university and a private company joined their efforts to create the Fractus® Antennas, the first antennas based on the fractal technology that operate simultaneously at GSM 900 MHz and DCS 1800 MHz. Such base-station antennas were designed to operate in a micro-cell environment and were awarded in December 1998, by the EuroCASE with the IST Grand Prize.
The aim of the talk is to give an broad overview on the fractal technology and to introduce some of the most recent advances and applications in the field.
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