Improved Antenna Design for Mobile Application In VHF Range

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Addis Ababa University


The wireless industry is witnessing an volatile emergence today in present era. Today’s antenna systems demand versatility and unobtrusiveness. Operators are looking for systems that can perform over several frequency bands or are reconfigurable as the demands on the system changes. Some applications require the antenna to be as miniaturized as possible. Fractal plays a prominent role for these requirements. Fractals have non-integral dimensions and their space filling capability could be used for miniaturizing antenna size and their property of being self-similarity in the geometry leads to have antennas which have a large number of resonant frequencies. Fractal antennas also have Multiband performance is at non-harmonic frequencies. Fractal antennas have improved Impedance, improved SWR(standing wave ratio) performance on a reduced physical area when compared to non fractal Euclidean geometries. Fractal antennas show Compressed Resonant behavior. At higher frequencies the Fractal antennas are naturally broadband. Polarization and phasing of Fractal antenna is possible. In many cases, the use of fractal element antennas can simplify circuit design. Often fractal antenna do not require any matching components to achieve multiband or broadband performance. Perturbation could be applied to shape of fractal antenna to make it to resonate at different frequency. In this thesis Koch fractal, Sierpinski Triangle, Sierpinski Carpet ,Julia fractal with different iterations have been generated using MATLAB. Koch fractal of length 5.1c.m. with different iterations as a monopole antenna have been simulated using MATLAB and EZNEC code which is a MININEC code, and show the desirable advantages of fractal antennas. Different three iteration Koch fractal monopoles have been studied for GSM900 and GSM1800 bands .The Koch monopole exhibits excellent performance at 925 MHz and 1800Mhz and has radiation properties nearly identical to that of traditional, straight-wire monopoles at that frequency. The greatest advantage of the Koch monopole design is compactness. A size reduction of nearly 50% was achieved over the straight-wire, , λ / 4 free-space monopole. This is highly significant for applications such as GSM cellular phones. Since it is half the size of the traditional monopole, it could easily be completely integrated within the case of the phone, eliminating the protruding monopoles commonly seen on many cellular phones. Since the radiation pattern is highly uniform and identical to that of a traditional λ / 4 monopole, it could be used in nearly any type of wireless communications receiver. The very similar gain to the traditional λ / 4 monopole is another benefit of the design. Another beneficial of fractal antennas is fractal antennas are in form of a PCB. Thus the Koch monopole presents an excellent, compact solution to the traditional straight-wire monopole.



Vhf Range