الفهرس 
Chapter 1: IntroductionOnly 14 pages are availabe for public view
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Abstract
Recently, terahertz (THz) technology has gained the interest of
researchers because of its emerging applications in spectroscopy,
communication, medical, military, imaging, sensing, and material
characterization.
This thesis introduces a study for graphene-based surfaces which
make use of its unique electrical, mechanical, optical, and thermal
properties. Graphene electrical conductivity and the effect of changing
the chemical potential (μc) on it, is explained in more details. Several
applications of graphene surfaces in antenna engineering have been
investigated in this thesis. Graphene is used in the design of 7 x 7
frequency selective surface unit-cell elements to enhance the gain of halfwavelength
dipole antenna from 1.4 dBi to 6.6 dBi, at 2.4 THz. The
passband and stopband filtering properties of the graphene FSS structure
are controlled by the graphene chemical potential. Electronic beam
switching is achieved by surrounding dipole antenna with decagon FSS
array with controlled filtering properties. Switching of single or multiple
beams can be obtained. The decagon side walls with biased FSS unit-cell
elements have passband filtering and the unbiased FSS unit-cell elements
have stopband filtering property. The beamwidth of the switched beam is
determined according to the number of the decagon side walls with
biased FSS unit-cell elements. Cylindrical polygon with ten faces covered
by this graphene based FSS unit cell-element is used to switch the beam
radiated from dipole antenna at its center in different directions by
controlling the chemical potential (μc) value on each polygon face.
Graphene based artificial magnetic conductor (AMC) planar array
Abstract
III
consists of 12 x 12 unit-cell elements is designed to act as a ground plane
for the dipole antenna for gain enhancement from 2.8 dBi to 4.68 dBi at 2
THz. It is used to convert the omni-directional dipole pattern into a
directive one.
Metamaterial surfaces based on graphene are investigated at THz
band. The graphene metamaterial (GMM) unit-cell element consists of
graphene two gaps split-ring-resonator (SRR) printed on a thick SiO2
substrate. The metamaterial parameters of the unit-cell element have been
calculated at different graphene chemical potentials and different SRR
gaps. The metamaterial unit-cell element introduces negative ɛr and μr
over a wide frequency band starting from 390 to 550 GHz. A reflectarray
unit-cell element based on the GMM is designed at different frequencies.
The phase compensation of the reflected waves is achieved by changing
the SRR gap width. Three different 13 × 13 GMM reflectarrays are
designed and analyzed at different graphene chemical potentials. A
maximum gain of 22.6, 19, and 21.5 dBi with side lobe level (SLL) is -
11.31/-9.15, -10.98/-5.31, and -7.31/-8.45 dBi in an E/H-plane for
different three reflectarray arrangements. An averaging phase curve is
calculated to construct a single structure GMM reflectarray with
frequency tunable radiation characteristics. A 13 x 13 unit-cell elements
graphene metamaterial reflectarray antenna fed by a circular horn antenna
is designed and analyzed at different graphene chemical potentials. Fullwave
analysis for the graphene metamaterial reflectarray antenna has
been applied using the finite integration technique.
GMM transmitarray is designed for terahertz applications. The
unit-cell element is a multilayered metamaterial structure of a graphene
split ring resonator with two variable gaps. The metamaterial properties
of the unit-cell element are investigated from 0.74 to 0.94 THz for
Abstract
IV
different conductivities. A parametric study of the transmission properties
of the metamaterial unit-cell element is investigated. The radiation
characteristics of 169 unit-cell elements of the three layers GMM
transmitarrays are analyzed for different applied DC voltages. The gain
and side-lobe level of the proposed transmitarray are improved by using
an averaging process on the transmission phase used for array
construction. The transmitarray introduces a high gain of about 18.5 dB at
frequencies 0.83, 0.85 and 0.88 THz for chemical potentials μc = 0.4, 0.5
and 0.8 eV, respectively.