الفهرس 
METHODS OF SOLUTION THE FINITEOnly 14 pages are availabe for public view
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Abstract
This thesis addresses the ground curvature effect on the characteristics of dielectric resonator antennas. The study is done in two parts. In The first part,the effects of ground curvature on the Characteristics of different elements of dielectric resonator antenna (DRA) are investigated. The first to be considered is the characteristics of cylindrical dielectric resonator antenna (CDRA)mounted on superquadric ground plane and again on triangular ground plane.To study the ground shape effect on radiation characteristics of the CDRA in different planes, the reflection coefficient, the input impedance, the copolarization and the cross-polarization characteristics are determined. Next, the characteristics of the CDRA on superquadric cylindrical body are analyzed.Curvature effects on radiation characteristics of CDRA in different planes are considered. The reflection coefficient, the input impedance, the co-polarization and the cross-polarization characteristics, gain of the antenna, are worked out for different values of ν ”squareness parameter”. Then the effect of changing the aspect ratio B/A on the reflection coefficient and the input impedance has been stdied. The effect of the ground plane cylindrical curvature on circular polarization CDRA element is determined, and then compensation of this effect by two methods is presented. At the end of this part the characteristics of hemispherical dielectric resonator antenna (HDRA) mounted on or embedded in spherical ground plane are investigated. Curvature effects on radiation characteristics of hemispherical DRA are evaluated. The co-polarization and the cross-polarization characteristics are analyzed. The structure of a superstrate-loaded hemispherical DRA is treated. The superstrate layer is loaded directly on the hemispherical DRA. The results obtained for the reflection coefficient, the input impedance and the radiation pattern in different planes are analyzed as functions of ground sphere radius and superstrate permittivity. Also, the effects of the spherical curvature on the characteristics of circular polarization DRA element mounted on or embedded in spherical structure are studied. The second part is devoted to using the previous results to consider
suitable applications of DRA over curved structures.The first application is that in some communication systems antennas are used on curved structures to get omnidirectional patterns. So, DRA
elements are used to get omnidirectional pattern suitable for mobile systems.
By studying the radiation characteristics of hemispherical dielectric resonator
antenna (HDRA) elements mounted on or embedded in a hollow circular
cylindrical ground structure, the performance of the DRA array which operates
at about 1.8 GHz is investigated. Factors influencing the array performance,
such as the number of elements and element spacing are explained. A
perforated dielectric technique is used to design the array from a single
dielectric sheet. The overall profile of the antenna can be significantly reduced.
The radiation patterns with respect to the number of DRA elements are
depicted. Then, the previous discussions are repeated for spherical ground
plane for comparison.
The second application considered is direction finding systems. By
studying HDRA array mounted on or embedded in a hollow circular cylindrical
ground structure and CDRA array mounted on or embedded in a pyramidal
ground structure, it has been possible to make use of such array in direction
finding systems. In the proposed arrays, only one DRA element is active and
the others are kept acting as parasitic. The direction of the received signal will
be determined using the relation between the received signals relative strengths
at each element of the array.
The third application is proposing a more compact handheld RFID
reader. The DRA mounted on cylindrical ground plane is investigated for
handheld RFID reader applications at 5.8 GHz. The simplicity of the structure
makes it practical in terms of cost, space, and ease of fabrication. The radiation
characteristics of the antenna in free space and in the presence of a proposed
compact reader device model and human hand are determined. The antenna is
circularly polarized and exhibits peak gain of 7.62 dB at 5.8 GHz with high
front to back ratio of 15.5 dB. Using the same reader device model, a
sequentially fed 2×2 DRA array mounted on the same cylindrical ground plane
is used for RFID reader antenna at 5.8 GHz. The array introduces high gain of
9.36 dB at 5.8 GHz with high front to back ratio of 10.48 dB. The 2×2 DRA
array elements exhibit circular polarization over a frequency band of 1.1 GHz.
The axial ratio is 1.1 dB at 5.8 GHz. The proposed reader model is simple and
has a small size compared with that in the case of planar ground plane case.
The fourth application considered is DRA reflectarray. For using
cylindrical and spherical dielectric resonator (DRA) reflectarray, a full-wave
analysis is carried out to study the case. The required phase shift for each DRA
element was realized by adjusting the height of the DRA element. Full-wave
analysis using the finite integration technique (FIT) is applied. The results are
validated by comparing it with that determined by the transmission line method
(TLM) and finite the element method (FEM).