الفهرس 
Chapter1 : IntroductionOnly 14 pages are availabe for public view
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Abstract
Reconfigurability can be obtained by using reconfigurable materials like graphene, plasma, and water or through switchable elements like positive intrinsic diodes and microelectromechanical systems. Reconfigurability also can be added to the antenna using supporting surfaces such as artificial-magnetic conductors, frequency-selective surfaces, and metamaterial surfaces.
At first different designs of frequency reconfigurable antennas are introduced. The first design is a frequency reconfigurable antenna based on transformer oil as a substrate for a four-arms center-fed antenna at microwave frequency bands. Transformer oil enables the proposed antenna to operate at different frequencies over a wide range from 5.21 GHz to 6.56 GHz. The second technique for frequency reconfigurability depends on graphene material that used to design a frequency tunable dipole antenna for THz applications. Using graphene allows the dipole antenna to operate over a wide band of 1.0 THz ranging from 0.2 THz to 1.2 THz.
Pattern reconfigurable antennas will also be introduced at microwave and terahertz bands. Using four PIN diodes with a four-arms center-fed antenna and a substrate of relative permittivity εr = 2.2 switches its radiation pattern into different four directions with a gain of maximum value of 8.72 dBi and HPBW of 45o at an operating frequency of f = 5.21 GHz. As well as the pattern reconfigurability of a designed dipole antenna is obtained at a frequency of f = 1.45 THz band using a 19 x 19 graphene-based AMC array by varying its conductivity. The proposed antenna’s radiation pattern is switched over the angle range with a maximum gain value of 4.34 dBi.
Antenna polarization reconfigurability between LP and CP will be obtained through AMC surfaces with different materials. The first one is a design based on a graphene artificial magnetic conductor surface. The graphene material’s controllable conductivity allows the change of electromagnetic wave polarization left-hand and right-hand circular polarization (CP) through electrical DC biasing. The gain enhancement of a V-shaped dipole antenna is achieved by backing it with an AMC array. The polarization conversion bandwidth is 19.44% for 7x7 AMC array. The second antenna used a single and dual-band FSS unit-cell elements and photoconductive switches. The single-band FSS unit-cell element exhibits frequency reconfigurability between 0.62 THz and 0.7 THz. The dual-band FSS-based unit-cell element exhibits frequency reconfigurability between (0.42 THz and 1.03 THz) when the switches are turned ON and (0.51 THz and 0.865 THz) when the switches are turned OFF. The FSS-based unit-cell element had a capability of polarization conversion over two bands from 0.46 THz to 0.56 THz and from 0.82 THz to 0.91 THz. It is then arranged in a 7 x 7 array and used as a reflector for a dipole antenna, enhancing its gain to 8.48 dBi and converting its polarization from LP to CP at 0.82 THz.
At the end of the thesis, two antenna characteristics are controlled simultaneously, obtaining multiple reconfigurable antennas. The designs of the proposed oil-based frequency reconfigurable antenna and the PIN diodes-based pattern reconfigurable antenna are combined, producing a frequency-pattern reconfigurable antenna.