Improved Antenna Design for Mobile Application In VHF Range
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Date
2012
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Addis Ababa University
Abstract
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.
Description
Keywords
Vhf Range