Sierpinski Gasket: Multiband Fractal Antenna for 4G Systems

Abstract

The evolution of the current systems to the 4G is based more and more on a key idea: interoperability. In the futures systems, a single terminal should be capable to work in anywhere, at any moment and in any interface, resulting in a convergence of services. Like this, the futures systems should be so much interoperable with the futures systems as with the legacy, in way to allow a soft migration among the several air interfaces. With the crescent growth of standards based on access techniques CDMA, the obtaining of the DOA becomes more and more necessary in way to implement SDMA systems. Following this, with the new techniques based on intelligent antennas capable to select the CDMA user wanted (UOA) and to discover the frequency and the delay profile of arrival (FOA and τOA), the use of antennas arrays is configured as indispensable technique in the modern systems. Multimode, multiband operation presents a formidable challenge to mobile phone designers, particularly for the RF parts. Of these, the antennas occupy the largest volume and, hence, have the biggest impact on the (commercially crucial) styling of the device. It is well-known that antenna bandwidth is proportional to volume. However, the space allocated to the antenna(s) has not increased: on the contrary, it is tending to decrease due to the demand for thinner, more highly stylized devices. If this were not enough, there is also increasing pressure on mobile phone manufacturers to improve performance, particularly in countries with areas of low population density, where, due to the large distances involved, cellular coverage is often “patchy.” The multiband antenna must be capable of providing a good gain and bandwidth compatible with the future and current systems. Such antenna should still offer good characteristics regarding its size and weight, so that it could be used in mobile, portable or fixed stations terminals. A natural way for these antennas has been the application of the fractal theory, which allows the project of multiband antennas with reduced sizes. This thesis discus the bowtie antenna geometry which is straightforwardly expanded to one of the simplest fractal antennas: the so-called Sierpinski fractal antenna or Sierpinski gasket. Very basically, the Sierpinski fractal is none other than a bowtie with a specially arranged hole structure. Fractal antennas are not broadband in the conventional sense but rather “multiband”. Detailed analysis of Sierpinski fractal antenna is done with its comparison with bow-tie antenna, the simulation is one based on method of moments (MoM) and is done using MATLAB®. Numerical results of the antenna radiation characteristics, including input impedance, input reflection coefficient, gain, radiated power and radiation pattern, are presented for mode-2 Sierpinski fractal and compared with that of a bowtie antenna. Discussion is also done on the use of fractal arrangements for the design of planar antenna arrays. Iterated Function System (IFS) is used to generate the fractal array (Sierpinski gasket). The antenna arrays are generated using MATLAB®, the resulting radiated field is calculated and comparison of two-dimensional periodic, random and fractal arrays is done in detail.