الفهرس | Only 14 pages are availabe for public view |
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. |