الفهرس 
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Abstract
This thesis proposes the analysis and design of reconfigurable metamaterials (MMs) for controlling and guiding electromagnetic waves. MM is a synthetic material that has negative permittivity and permeability in the same frequency spectrum. It possesses unique properties not seen in natural materials, allowing it to improve antenna parameters such as gain, bandwidth, and wave polarization manipulation.
Today, transmitting and receiving systems are under more strain than ever before due to the need for increased functionality in a small space. This difficulty can be solved by using reconfigurable antennas. Changing the frequency, polarization, or radiation characteristics of an antenna allows it to be reconfigured. To achieve this modification, many strategies that redistribute antenna currents and therefore modify the electromagnetic fields of the antenna’s effective aperture are utilized. This notion can dramatically reduce the number of components in communication systems, as well as their hardware complexity and cost.
Reconfigurable antennas are designed using the properties of graphene material. Antennas with beam-switching capability allow transmitting directive beams with the same frequency in different directions to serve multiple applications. They have drawn interest in radar, smart tracking, satellite, navigation, and mobile systems.
First, a reconfigurable monopole antenna with dimensions 75×75 mm2 residing on an electromagnetic bandgap (EBG) is proposed. Monopole antenna operates at 5 GHz, which is loaded by EBG, and the intended EBG provides a bandgap in the range of frequency from 4 to 9.8 GHz. A coaxial cable feeds the monopole antenna and is connected to the inner wire. A single monopole denotes matching bandwidth from 4.6 GHz to 5.3 GHz, with a gain of 8 dBi. The antenna is designed for 4G/5G applications in tracking and healthcare systems. Graphene material is used to achieve a reconfigurable beam between four monopole antennas. The beam is switched toward the direction of biasing monopole at four different angles (+45o,0o, -45o,180o). Four monopole antennas structure is proposed and offered 7.82 dBi constant gain in all four beam directions and gives the same reflection coefficient band. Eight monopole antenna structures are located at 0o,45o, 90o,135o,180o, 225o, 270o, and 315o with little decrease in gain to 7.2dBi.
Second, the application of Ridge Gap Waveguide (RGWG) substrate formed by metamaterial unit cell mushroom for enhancing the Dielectric Resonator Antenna (DRA) performance is proposed. The designed RGWG introduces bandgap behaviour in the frequency band from 45 to 92 GHz and operates at 60 GHz. Hemispherical Dielectric Resonator Antenna (HDRA) is combined with the RGWG substrate by crossed slots, one of these slots is rotated by 45o in a clockwise direction to achieve left-hand circular polarization (CP), and the other is rotated by 135oin anticlockwise direction to achieve right-hand CP. For switching between the crossed slots, graphene material is used. The HDRA has 0.98 GHz CP bandwidth and 7 dBi gain when using a single element HDRA structure. To improve the gain and axial ratio, 2×1 HDRA MIMO elements are used to enhance the gain and CP bandwidth to 8.31dBi and 1GHz, respectively. 2×2 MIMO antenna structure is designed by placing two elements of 2×1 configuration orthogonal to each other to enable achieving a perfect transmission coefficient, diversity gain, envelop correlation coefficient, and multiplexing efficiency.
In addition, a new design of linear polarized circle spiral antenna is proposed to achieve circular polarization by using spiral characteristics. Two armchairs are arranged above a slotted plate to form an antenna structure. The reflection coefficient of a single spiral antenna element is offered matching band 1.2 GHz around 60 GHz.
Finally, different shapes of PMA (Perfect Metamaterials Absorber) are proposed. A single PMA unit cell based on a T-shape resonator is suitable for X-band applications. A dual resonances PMA structure is becoming a prime technology for many presents and future wireless communication systems. The absorber is used to reduce the radar cross-section (RCS) and improve the stealth ability of objects.
In metamaterial absorber designs, graphene sheets are utilized to modify the propagation path of electromagnetic waves and improve the absorption performance of structures. The dual-band graphene structure is used graphene material to obtain a wide dual-band, the design contains two T-shapes of graphene with similar dimensions h2×h1=8.2mm×3mm on top of the FR-4 substrate. The structure has two double bands matching the first band from 9.1GHz to 10.1GHz, and the second band from 12.5GHz to 13GHz. The absorption peak reached 88% in the first band and 85% in the second band. The triple band graphene absorber contains four T-shapes of graphene every two T-shapes have similar dimensions. The proposed structure gives absorption wide peaks at 9.5, 13.5, and 15.6 GHz with the absorption of 92.5, 99.8, and 97%, respectively.