الفهرس 
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Abstract
Microstrip patch antennas are used in a wide range of applications due to their low cost, conformability, light weight, small volume, case of manufacture, and ability to be integrated with microwave integrated circuits (MICs). Due to the above advantages of patch antennas, they have become very popular in various applications ranging from aircrafts, rockets, spaceships, vehicular communications, and remote sensing to radiators in biomedical applications. The present thesis is concerned with the analysis of the popular patch antennas (rectangular, square, circular and annular-ring) over isotropic (homogeneous and inhomogeneous), uniaxial anisotropic dielectric and fenite substrates using the FDTD method. Different categories of problems have been successfully solved using this scheme. Several absorbing boundary conditions (ABCs) technique such as; Mur’s first order ABC, local ABC, and the perfectly matched layer (PML) ABC are used to terminate patch antennas under consideration. The time domain response, the return loss, the input impedance and the radiation patterns of the above patch antennas are obtained. It has been shown that the results obtained by the FDTD of the patch antennas under consideration are found to be in good agreement with the published theoretical and experimental data. The most serious shortcoming of the patch antenna is its narrow bandwidth. Different techniques were used to overcome this problem. The two straightforward techniques are the use of gap-coupled parasitic patches and the stacked patches. In this work, the above mentioned techniques besides the hybridization of them are considered. 10 -dB return loss-bandwidth of 40% has been achieved for stacked gap-coupled circular patch antennas on isotropic substrates. Also, 27 % 10-dB return loss bandwidth has been achieved for the stacked gap- coupled ring patch antennas on isotropic substrates. The problems of both the rectangular patch antenna over a multi-layer substrate and the two- Iayer (EMC) rectangular patch antenna are also studied. from the numerical results obtained by the FDTD method it can be concluded that the two-layer (EMC) patch provides an increase in the bandwidth by 2.8 times in the case of a single layer patch. In addition, one can read significant improvement in the E-plane pattern of the above structures. The effect of changing the air gap layer thickness of the above antennas is studied. from the obtained numerical results, one can find significant improvement in the E-plane pattern of multi-layer patch as the air gap layer thickness is increased. However, for the two- layer (EMC) rectangular patch antenna one can observe that the 10-dB return loss bandwidth is decreased and the 3- dB beam width of that antenna is increased as the air gap layer thickness is increased. In the present work, the concept of cxtcrnal substrate perforation is applied to rectangular and circular patch antennas over inhomogeneous isotropic substrates to overcome the problem of surface waves and to enhance the performance of the above patch antennas. Two approaches based on removal of the substrate under the patch or etching spaced periodic dielectric or air holes in the substrate are considered.