Improved Antenna Design For Mobile Application In Vhf Range

The wireless industry is witnessing an volatile emergence today in present era.rnToday’s antenna systems demand versatility and unobtrusiveness. Operators arernlooking for systems that can perform over several frequency bands or arernreconfigurable as the demands on the system changes. Some applications require thernantenna to be as miniaturized as possible. Fractal plays a prominent role for thesernrequirements. Fractals have non-integral dimensions and their space filling capabilityrncould be used for miniaturizing antenna size and their property of being self-similarityrnin the geometry leads to have antennas which have a large number of resonantrnfrequencies. Fractal antennas also have Multiband performance is at non-harmonicrnfrequencies. Fractal antennas have improved Impedance, improved SWR(standingrnwave ratio) performance on a reduced physical area when compared to non fractalrnEuclidean geometries. Fractal antennas show Compressed Resonant behavior. Atrnhigher frequencies the Fractal antennas are naturally broadband. Polarization andrnphasing of Fractal antenna is possible. In many cases, the use of fractal elementrnantennas can simplify circuit design. Often fractal antenna do not require anyrnmatching components to achieve multiband or broadband performance. Perturbationrncould be applied to shape of fractal antenna to make it to resonate at differentrnfrequency.rnIn this thesis Koch fractal, Sierpinski Triangle, Sierpinski Carpet ,Julia fractalrnwith different iterations have been generated using MATLAB. Koch fractal of lengthrn5.1c.m. with different iterations as a monopole antenna have been simulated usingrnMATLAB and EZNEC code which is a MININEC code, and show the desirablernadvantages of fractal antennas. Different three iteration Koch fractal monopoles havernbeen studied for GSM900 and GSM1800 bands .The Koch monopole exhibitsrnexcellent performance at 925 MHz and 1800Mhz and has radiation properties nearlyrnidentical to that of traditional, straight-wire monopoles at that frequency. The greatestrnadvantage of the Koch monopole design is compactness. A size reduction of nearlyrn50% was achieved over the straight-wire, , λ / 4 free-space monopole. This is highlyrnsignificant for applications such as GSM cellular phones. Since it is half the size ofrnthe traditional monopole, it could easily be completely integrated within the case ofrnthe phone, eliminating the protruding monopoles commonly seen on many cellularrnphones. Since the radiation pattern is highly uniform and identical to that of arntraditional λ / 4 monopole, it could be used in nearly any type of wirelessrncommunications receiver. The very similar gain to the traditional λ / 4 monopole isrnanother benefit of the design. Another beneficial of fractal antennas is fractal antennasrnare in form of a PCB. Thus the Koch monopole presents an excellent, compactrnsolution to the traditional straight-wire monopole.

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