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Abstract
Antenna design plays an important role in wireless communication systems. Most of the recent systems require antennas that have compact small sizes, low profile with broadband performance and high efficiency as well as capability to be embedded in integrated circuits.
The main purpose of this thesis is to study, design and implement planar slot antennas with fractal shapes. The two-presented designs in this thesis are mainly using Sierpinski fractal shapes together with slot topology to develop antennas either with broadband or circularly polarized performance.
One of the new shapes introduced in antenna designs is the fractal shape. Fractal shapes are composed of similar structures with different scales. This shape makes them a good candidate to design multi-band antennas. From this comes the main aim of thesis to improve the bandwidth of fractal shapes especially the Sierpinski fractal family, which is commonly known by its multi-band behavior.
On the other side, Slot antennas show a better performance over patch antennas. Slot antennas exhibit a broadband performance, high efficiency and ease in fabrication and can be easily embedded with integrated circuits. From the above shown advantages, Slot antennas appear to be a good candidate to develop the multi-band behavior of Sierpinski family to a broadband one.
The first proposed antenna uses a slot version of Sierpinski shape to develop a broadband antenna. This is done by converting the ordinary Parany patch shape (one of the Sierpinski family) to a slot shape. Then some extra triangle slots are added to the Parany slot shape till reach the final design form. The final design is implemented on dielectric constant of 2.17 and height 0.787mm and fed using microstrip line using proximity-feeding technique. The design is performed using the 3D electromagnetic simulators HFSS® and Zeland. The design has flare angle of 90? and height 20 mm. The measured antenna shows a broadband performance of 60% in the range of 3 to 5.57 GHz for antenna return loss less than 10 dB (S11< –10 dB). The antenna shows an average gain of 2.5 dBi and efficiency of 94% as well as stable radiation patterns all over the band.
The second design in this thesis also uses the slot Sierpinski structures to design a circularly polarized antenna. First four Slot Sierpinski triangles of flare angle of 90? are grouped to create a square symmetrical fractal shape. These created shapes can be considered a new family of fractal shapes where its iteration changes by changing the basic Sierpinski unit forming it. Then an asymmetry is introduced to obtain a circularly polarized antenna. The design is performed also using the 3D electromagnetic simulators HFSS® and Zeland. The antenna is fabricated on dielectric constant 3.5 and height 0.76mm. The proposed configuration provides a compact area of 20 x 20 mm², a 3dB axial ratio bandwidth of 28% in the range from 8.6 to 11.4 GHz. The antenna also has high radiation efficiency of 97% and average gain of 4 dBi all over the operating band.