الفهرس 
Chapter1:IntroductionOnly 14 pages are availabe for public view
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Abstract
Ultra Wide Band (UWB) wireless communications offers a radically different
approach to wireless communications compared to conventional narrow band
systems. UWB technology received a major assistance in 2002 since the US
federal communication commission (FCC) allowed the authorization of using the
unlicensed frequency band between 3.1 to 10.6 GHz. The UWB has features such
as low cost, small size, more security, low power consumption, Also the FCC
allocated an absolute band width up to 7.5 GHz which is about 110% fractional
band width at the center frequency this large band with spectrum is available for
high data rate communications. UWB antenna with frequency notch characteristics
need to be designed to suppress radiation to obviate interference of UWB system
with the other narrow band systems as WLAN, WiMAX, and X- band. Recently
many UWB monopole antennas with single or multiple notch frequencies to avoid
this interference have been developed. The band-notch characteristics can be
achieved through various slots or slits in the radiating patch, slots in the feed line,
and slots in the ground plane or using parasitic patches. However, these antennas
have fixed band-notch characteristics, and in the cases that there is no interference,
they are unable to utilize all the UWB frequency range. Hence, using
reconfigurable band-notch structure we can improve the performance of the UWB
system. In reconfigurable band-notch UWB antennas, changing the notch
frequency is achieved by using lumped elements such as PIN diodes or varactor
diodes. PIN diodes are used as a switch by applying a dc voltage on its terminals.
UWB antennas with PIN diodes have only two different notch frequencies or less.
Varactor diodes are used as a variable capacitance depending on the applied
reverse bias DC voltage, to achieve different notch frequencies. This thesis focuses on achieving a simple reconfigurable band-notch UWB
antenna. Extensive investigations are also conducted on three different types of
miniaturized UWB antennas.
The First type, a new band notched Ultra-Wide Band (UWB) monopole antenna
using EBG is designed and tested. The Electro-Magnetic Band Gap (EBG) is
loaded besides micro strip line to reject one frequency. Other frequency notches
can be tuned by varying the width of EBG.
The second type, is a simple reconfigurable band-notch UWB antenna using single
varactor diode. A slot in the micro strip line is made and optimized to be loaded
later by a single varactor diode. The frequency band notch is achieved simply by
using a single capacitor element. The re-configurability can be done by using a
variable capacitor or a varactor diode instead of using single capacitor element.
Hence, the notch frequency tuning is achieved by applying a different reverse DC
voltage on the varactor terminals. The effect of changing the varactor position is
also examined. Finite element method (FEM) in the frequency domain and finite
integration technique (FIT) in the time domain are used to simulate the proposed
structures using Ansys HFSS and CST MWS, respectively. Two prototypes of the
proposed antenna with a rectangular slot are fabricated, each with a different single
capacitor element. Their return losses are measured and compared with the
simulated ones. To ensure tunability, two different capacitor elements with
capacitances 0.6 and 1.5 pF are used, which are available in our laboratory. Two
notch frequencies are obtained at 6.1 and 4.3 GHz, respectively. Very good
agreement between measured and simulated results has been observed.
The third type, is a simple reconfigurable band notch UWB antenna using
cylindrical DRA. A slot is made on feed line to be loaded by single varactor diode.
A wide range of frequency band-notches, which cover almost all the narrow band
coexistence systems, can be obtained simply by changing the capacitance value And position. Finite element method (FEM) in the frequency domain and finite
integration technique (FIT) in the time domain are used to simulate the proposed
structures using Ansys HFSS and CST MWS respectively.