الفهرس 
Problem DefinitionOnly 14 pages are availabe for public view
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Abstract
Antenna arrays are usually designed to obtain directive beams in different applications. Different types of antenna arrays are used such as transmit arrays, and reflectarrays. Reflectarrays have been widely used to take place of the traditional bulky reflector antennas. Frequently, reflectarrays are designed on planner substrates of dielectric materials. The design method of the reflectarrays depends on the segmentation of the array into patches or cells and each patch incurs a phase shift to the incident beam to direct it in a certain direction. The art of designing a reflectarray for a special purpose at a specific frequency is how to select the appropriate unit cell shape, size, and orientation at each position on the reflectarray surface. The design method of the reflectarray begins with the selection of the unit cell shape, the optimization of the unit cell dimensions to work at the required design frequency, and the estimation of the reflection phase curve of the unit cell versus a control parameter for the unit cell dimensions or orientation. This thesis studies the process of reflectarray design subject to certain requirements and constraints. Different unit cells are suggested in this thesis for reflectarray design in the millimeter wave range for proper operation in 5G communication. The characteristics of the suggested unit cells are studied and the reflection phase curves are studied and compared. These reflection phase curves are used to build reflectarrays at 28 GHz with both center feeding and offset feeding. Two different scenarios are considered in the thesis; single beam reflectarrays and double beam reflectarrays. Each designed reflectarray is analyzed from the gain and bandwidth perspectives. A comparison study is given between the designed reflectarrays. Moreover, it has been notices in the literature works that there is a drift of the maximum gain achieved by any reflectarray from the design frequency. A robust solution for this problem is presented in the thesis based on optimization with a proposed phase gradients approach to build hybrid reflectarrays with multiple unit cells. The design with the proposed phase gradients strategy succeeds in achieving a maximum gain at the design frequency. It can also benefit from any unit cell with linear phase characteristics even if the linear portion of the phase characteristics is limited. In addition, a reflectarray design with an all metal cell is presented in the thesis and compared with microstrip planar reflectarrays due to the good linearity of the characteristic phase curves of the metal unit cells. The obtained gain and bandwidth levels from the designed reflectarrays are promising to be used in the suggested 5G applications at the base stations.