Since the isolation of graphene in 2004, a large amount of research has been directed at 2D materials and their applications due to their unique characteristics. This thesis delivers pioneering developments on the applications of graphene and graphene oxide (GO) on electromagnetic ranges such as radio frequency, microwave frequency and THz bands, and specifically 2D materials based antennas, absorbers, sensors and etc. This thesis focuses on exploring electromagnetic applications of monolayer graphene, printed graphene and graphene oxide. In study of monolayer graphene applications, the theoretical and simulation studies are carried out to design tunable terahertz (THz) absorbers, tunable microwave wideband absorbers, and reconfigurable antennas, etc. These studies on the applications of monolayer graphene have proved prospective potentials of graphene in THz sensing, RCS reduction, and reconfigurable antennas. This thesis also presents pioneering advances on electromagnetic applications of printed graphene. Among these works, low-cost highly conductive and mechanically flexible printed graphene is developed for radio frequency (RF) applications. For the first time, effective RF radiation of printed graphene is experimentally demonstrated. Based on these results, applications of printed graphene including RFID (radio frequency identification) tags, anti-tampering RFID, EMI shielding, flexible microwave components such as transmission lines, resonators and antennas, conformable wideband radar absorbers, graphene oxide based wireless sensors, etc. are developed and experimentally demonstrated. This work significantly expands applications of graphene in electromagnetic areas.

Lee Wai Ki. / Thesis submitted in: May 2004. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references (leaves 62-66). / Abstracts in English and Chinese. / Chapter Chapter 1: --- Introduction --- p.8 / Chapter 1.1 --- Motivation --- p.8 / Chapter 1.2 --- Organization of the thesis --- p.10 / Chapter Chapter 2: --- Background Technology --- p.12 / Chapter 2.1 --- Introduction: FUZZY EM CAD formula for impedance of the edge of the patch antenna --- p.12 / Chapter 2.2 --- Fringe field extension of the patch: --- p.12 / Chapter 2.2.1 --- Applying the root of area capacitance formula --- p.12 / Chapter 2.2.2 --- Defining microstrip parallel plate capacitor with infinite substrate --- p.13 / Chapter 2.2.3 --- The parallel plate capacitor formula --- p.14 / Chapter 2.2.4 --- DC fringe field leading to the patch extension --- p.15 / Chapter 2.3 --- Cavity model of the patch --- p.16 / Chapter 2.3.1 --- Cavity model analysis on its internal field --- p.16 / Chapter 2.3.2 --- Input impedance derived from cavity model --- p.19 / Chapter 2.3.3 --- Quality factor of patch antenna --- p.19 / Chapter 2.4 --- Fringe extension applied to cavity model in RF --- p.23 / Chapter Chapter 3: --- Simple one Port wide band multi-layer patch Antenna --- p.24 / Chapter 3.1 --- Introduction --- p.24 / Chapter 3.2 --- Antenna design --- p.25 / Chapter 3.3 --- Measured results --- p.26 / Chapter 3.4 --- Antenna Analysis --- p.29 / Chapter 3.5 --- Conclusion --- p.30 / Chapter Chapter 4: --- Design synthesis of patch antennas of the T-square Probe --- p.31 / Chapter 4.1 --- Introduction --- p.31 / Chapter 4.2 --- The physics interpretation --- p.32 / Chapter 4.3 --- The Smith chart movement by the T-square feed on the patch --- p.33 / Chapter 4.4 --- Conclusion --- p.35 / Chapter Chapter 5: --- Design synthesis of the wideband tuning-fork-shaped feeding for patch antenna --- p.36 / Chapter 5.1 --- Introduction --- p.36 / Chapter 5.2 --- Antenna design --- p.36 / Chapter 5.3 --- The Smith chart movements of the tuning-fork shaped feeding on the patch --- p.37 / Chapter 5.4 --- Conclusion --- p.41 / Chapter Chapter 6: --- "Fork on H-slot feed of multilayer microstrip antenna for wideband, high isolation and low cross polarization" --- p.42 / Chapter 6.1 --- Introduction --- p.42 / Chapter 6.2 --- Antenna analysis - Isolation improvement considerations --- p.44 / Chapter 6.3 --- Antenna design and measured results --- p.46 / Chapter 6.3.1 --- The simulated return loss and current distribution s in various structure of the two port. --- p.47 / Chapter 6.3.2. --- The hardware and the comparison of results --- p.50 / Chapter 6.3.3. --- The simulated properties of the radiation patterns and cross-polarizations --- p.52 / Chapter 6.3.4. --- The comparison of radiation patterns between simulation and hardware --- p.56 / Chapter 6.4 --- Further improvements --- p.58 / Chapter 6.5 --- Conclusion --- p.59 / Chapter Chapter 7: --- Conclusions --- p.60 / Reference --- p.62 / List of Publication --- p.66

Yim, Ho Yan. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2007. / Includes bibliographical references (leaves 125-128). / Abstracts in English and Chinese. / Abstract --- p.ii / 論文摘要 --- p.iv / Acknowledgement --- p.vi / Table of Content --- p.vii / List of Figures --- p.x / List of Tables --- p.xiv / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Filter --- p.3 / Chapter 1.2 --- Antenna --- p.4 / Chapter 1.3 --- Outline of the Thesis --- p.6 / Chapter Chapter 2 --- Basic Theories in Filter and Patch Antenna Design --- p.7 / Chapter 2.1 --- Microwave Filter Design --- p.7 / Chapter 2.1.1 --- Transfer Functions --- p.8 / Chapter 2.1.2 --- Lowpass Prototype Filters and Elements --- p.14 / Chapter 2.1.3 --- Filter Transformations --- p.18 / Chapter 2.1.4 --- Admittance Inverter --- p.21 / Chapter 2.2 --- Antenna Concepts --- p.23 / Chapter 2.2.1 --- Microstrip Antenna --- p.23 / Chapter 2.2.2 --- Patch Antenna Design --- p.24 / Chapter 2.2.3 --- Polarization --- p.28 / Chapter Chapter 3 --- Review of Conventional Dual-band Filter Designs --- p.33 / Chapter 3.1 --- Bandstop / bandpass Filters in a Cascade Connection --- p.33 / Chapter 3.2 --- Stepped Impedance Resonator --- p.34 / Chapter 3.3 --- Tunable Transmission Zero for Spurious Responses Suppression --- p.36 / Chapter 3.4 --- Comparison --- p.38 / Chapter Chapter 4 --- Novel Dual-band Filter Design with Equal Bandwidth --- p.39 / Chapter 4.1 --- Introduction --- p.39 / Chapter 4.2 --- Frequency Behavior of Shunt Stubs --- p.39 / Chapter 4.3 --- Dual-band Resonator with Paralleled Stubs --- p.42 / Chapter 4.4 --- Dual-band Admittance Inverter --- p.47 / Chapter 4.5 --- Dual-band Filter Realization --- p.51 / Chapter 4.5.1 --- Simulation Examples --- p.54 / Chapter 4.5.2 --- Comparison of Simulation results --- p.60 / Chapter 4.5.3 --- Experimental Results --- p.64 / Chapter Chapter 5 --- Novel Dual-band Filter Design with Unequal Bandwidth --- p.70 / Chapter 5.1 --- Introduction --- p.70 / Chapter 5.2 --- Dual-band Resonator using Step-Impedance Line --- p.70 / Chapter 5.3 --- Dual-band Admittance Inverter --- p.74 / Chapter 5.4 --- Dual-band Filter Realization --- p.75 / Chapter 5.4.1 --- Comparison of Simulation Results --- p.81 / Chapter 5.4.2 --- Experimental Results --- p.85 / Chapter Chapter 6 --- Review of Conventional CP Antenna Designs --- p.91 / Chapter 6.1 --- Degenerated Mode Patch --- p.91 / Chapter 6.2 --- CP Stacked Microstrip Patch Antenna Array --- p.92 / Chapter 6.3 --- Coplanar Waveguide-fed Slot Antenna --- p.93 / Chapter 6.4 --- Dual-band CP antenna fed by 2 different 90° hybrid couplers --- p.95 / Chapter Chapter 7 --- Novel New Dual-band CP Antenna Design --- p.96 / Chapter 7.1 --- Introduction --- p.96 / Chapter 7.2 --- Dual-band CP Patch Antenna --- p.96 / Chapter 7.2.1 --- Slotted Square Patch Antenna --- p.96 / Chapter 7.2.2 --- Slotted Cross Patch Antenna --- p.99 / Chapter 7.2.3 --- Simulation Results: Slotted Cross Patch Antenna --- p.101 / Chapter 7.3 --- Dual-band Quadrature Hybrid --- p.104 / Chapter 7.3.1 --- Simulation Results: Dual-band Hybrid Coupler --- p.107 / Chapter 7.4 --- Dual-band CP Antenna Realization --- p.113 / Chapter 7.4.1 --- Antenna Configuration --- p.113 / Chapter 7.4.2 --- Measurement Setup --- p.114 / Chapter 7.4.3 --- Experimental Results --- p.115 / Chapter Chapter 8 --- Conclusions and Recommendations for Future Work --- p.123 / Chapter 8.1 --- Filter --- p.123 / Chapter 8.2 --- Antenna --- p.123 / Chapter 8.3 --- Recommendations for future work --- p.124 / References --- p.125 / Author's Publications --- p.128 / Acronyms and Abbreviations --- p.129

by Chong Man Yuen. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1997. / Includes bibliographical references (leaves 125-128). / Dedication / Acknowledgements / List of Figure / List of Table / List of Appendix / Chapter 1. --- Introduction / Chapter 1.1 --- Background / Chapter 1.2 --- Ultra-Wide Band Antenna / Chapter 1.3 --- Finite Element Method (FEM) / Chapter 1.3.1 --- Domain Discretization / Chapter 1.3.2 --- Formulation of Variational Method / Chapter 2 --- Theory / Chapter 2.1 --- Variational principles for electromagnetics / Chapter 2.1.1 --- Construction of Functional / Chapter 2.2 --- Artificial Boundary / Chapter 2.2.1 --- Absorbing Boundary Conditions / Chapter 2.2.2 --- Perfectly Matched Layer (PML) / Chapter 2.3 --- Edge Basis Function / Chapter 2.4 --- Slotline Analysis / Chapter 3 --- Implementation of FEM / Chapter 3.1 --- Formulation of Element matrix / Chapter 3.2 --- Mesh Generation / Chapter 3.3 --- Assembly / Chapter 3.4 --- Incorporation of Boundary Conditions / Chapter 3.5 --- Code Implementation / Chapter 4 --- Finite Element Simulations / Chapter 4.1 --- Slotline / Chapter 4.2 --- Artificial Boundary of the domain / Chapter 4.3 --- Slotline Taper Junction / Chapter 4.4 --- Slotline Bowtie Junction / Chapter 5 --- Conclusion / Appendix A1 / Appendix A2 / Appendix A3 / Bibliography

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1980. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / by William Howard Hanot. / M.S.

En focalisant le rayonnement dans les directions utiles, les antennes directives ouvrent de nouvelles perspectives pour les applications sans-fil en termes de sélectivité spatiale, d'impact environnemental électromagnétique et de modes d'utilisation. Cependant les techniques classiques pour augmenter la directivité aboutissent souvent à une augmentation de la taille de l'antenne rendant difficile l'intégration dans les petits objets communicants. Cette difficulté est particulièrement critique pour les gammes de fréquences inférieures au gigahertz, lorsque l'on vise une intégration dans des objets dont les dimensions sont limitées à quelques centimètres. Le contrôle du rayonnement reste un enjeu important pour les radiocommunications futures afin de réduire les pollutions électromagnétiques qui limitent l'acceptabilité des communications sans-fil et la cohabitation des systèmes. L'état de l'art récent dans le domaine des antennes miniatures a montré de nouvelles perspectives pour l'établissement de super-directivité ; c'est-à-dire pour dépasser la directivité naturelle faible des systèmes antennaires miniatures. Ces perspectives reposent sur l'utilisation de réseaux d'antennes parasites miniatures pour construire un rayonnement directif. De plus, les activités de recherche dans le domaine des antennes actives ces dernières années permettent d'envisager une approche moderne aux problématiques liées à la directivité des antennes miniatures. Ces travaux de thèse ont pour objectif d'évaluer les perspectives d'améliorations qu'apporte l'électronique active aux problématiques des antennes miniatures directives. Des circuits au comportement particulier sont notamment mis en œuvre et évalués expérimentalement pour concrétiser ces nouvelles perspectives. / Directive antennas, used to focus the radiation in useful directions, offer new perspectives for wireless applications in terms of spatial selectivity, electromagnetic environmental impact and possible uses. Nevertheless, usual techniques to enhance antennas’ directivity lead to larger antennas and their integration into small objects would be difficult. That becomes critical when antennas working at less than 1 GHz frequencies have to be integrated in small objects (around few centimeters). Radiation control through directive antennas is being an important issue for the future communications. This kind of antennas allows reducing electromagnetic pollutions which limit wireless systems and communicants objects cohabitation. Recent state of the art shows new perspectives to establish small antennas with super directive radiation using parasitic antenna arrays. A super directive antenna is a small antenna that exceeds its natural and low directivity. Moreover, these last few years, researches on active antennas and associated results could be considered for modern approach to deal with small and directive antennas’ issues. In this work, we propose to evaluate the enhancement perspectives brought by the active electronic circuits to solve the small and directive antennas’ issues. Typically, special active circuits are designed and experimentally evaluated to materialize those antennas perspectives.

Conformal antennas have widespread applications in communication systems for vehicular bodies, aircrafts, and spacecrafts etc. They are non-protruding and can arbitrarily take any shape on the surface where they are etched. This thesis is a summary of two main projects. The first project employs a conformal array of four S-band and four GPS-band antennas for sub-payload of a sounding rocket. The sub-payload is a small cylinder and therefore the eight conformal antennas are based on curved patch geometry. The second project employs a conformal antenna for a CubeSat. The antenna is based on a cavitybacked slot and therefore can be conveniently integrated around the surface-mount solar cells of the CubeSat. Such an integration has enormous merits for CubeSat because there is no competition between the antennas and solar cells for the limited surface real estate. The antenna design operates UHF band with circular polarization, making it the first UHF nondeployed antenna for CubeSats. For both projects, problems such as isolation, impedance bandwidth, axial ratio bandwidth, and EMI shielding have been analyzed and resolved. This thesis work yields a prototype-ready design for the first project, and a final prototype and measurements for the second project.

This thesis work presents an innovative solution for small satellite antennas by integrating slot antennas and solar cells on the same panel to save small satellite surface real estate and to replace deployed wire antennas for certain operational frequencies. The two main advantages of the proposed antenna are: 1) the antenna does not require an expensive deployment mechanism that is required by dipole antennas; 2) the antenna does not occupy as much valuable surface real estate as patch antennas. The antenna design is based on using the spacing between the solar cells to etch slots in these spaces to create radiating elements. The initial feasibility study shows it is realistic to design cavit-backed slot antennas directly on a solar panel of a cube satellite. Due to the volume of the satellite, it is convenient to design antennas at S band or higher frequencies. Although it is possible to design integrated solar panel antennas in lower frequencies, such research is not the scope of this thesis work. In order to demonstrate and validate the design method, three fully integrated solar panel antennas were prototyped using Printed Circuit Board (PCB) technology (PCB is a common solar panel material for small satellites). The first prototype is a circularly polarized antenna. The second is a linearly polarized two-element antenna array. The third prototype is a dual band linearly polarized antenna array. Measured results agree well with simulations performed using Ansoft's High Frequency Structure Simulater (HFSS). The thesis also presents a feasibility study of optimization methods and reconfigurable solar panel antenna arrays. The optimization study explores methods to use genetic algorithms to find optimal antenna geometry and location. The reconfigurable study focuses on achieving different antenna patterns by switching on and off the slot elements placed around the solar cells on solar panels of a cube satellite. It is shown that the proposed integrated solar panel antenna is a robust and cost-effective antenna solution for small satellites. It is also shown that given a solar panel with reasonable size, one can easily achieve multiple antenna patterns and polarization by simple switching.

With the rapid of growth of wireless connectivity more demand is placed on the need for innovative technologies capable of satisfying increasing user demand and network capacity. Adaptive antennas systems or most commonly known as Smart Antennas are expected to be implemented in the next generation of wireless systems. Their implementation avails in dynamic adaptation to spatial and temporal conditions affecting the quality of communication, while offering tremendous flexibility to wireless providers. However one of the major challenges facing Smart Antenna technology is the inherent complexity of the antenna structure, associated control algorithm and implemented RF components possibly contributing to the delay of commercial interest. This thesis will present various adaptive antenna configurations that utilize an embedded dielectric in order to achieve significant size reduction and mechanical rigidity while maintaining favorable electromagnetic performance. In order to constrict the lateral ground plane dimension, a cylindrical shaped hollow ground skirt was attached to the antenna structures effectively compromising between effective beam forming in the azimuth plane and physical size. The complexity of these antenna structures requires a more contemporary design approach which involved computer modeling using a commercial available Finite Element software package and optimization using a developed generic Genetic Algorithm based optimization program. A dielectric embedded 7-element monopole array antenna featuring switched parasitic elements is presented and optimized for maximum vertically polarized gain in the horizontal plane, producing an antenna structure with a radial length of less then 0.25λ and total height of 0.4&alamba which was shown to radiate a main lobe beamwidth of 80 degrees with an absolute gain of 4.8dBi at 2.45GHz. Further on a dielectric embedded 7-element monopole array antenna featuring parasitic elements terminated with finite set of terminating reactive loads is presented with a radial length of less then 0.25&alambda and total height of 0.4&alambda. The antenna structure and reactive load combination were optimized for maximum horizontal gain producing a principal main lobe with a measured gain of 5.1dBi and beamwidth of 110 degrees at 2.48GHz. Finally it was shown single and dual radiation lobes maybe produced when active monopoles elements are placed eccentric in a circular shaped dielectric material. A circular array of elements embedded in a dielectric material was realized with measured gains of single and dual beam radiation at 2.45GHz was shown to be 5.18dBi and 3.65Bi respectively with corresponding beamwidths of 78.5 degrees and 53 degrees.

The application of the finite-difference time-domain (FDTD) method for the numerical analysis of complex electromagnetic problems related to wireless communications is considered. Since exact solutions to many complex electromagnetic problems are difficult, if not impossible, the FDTD method is well suited to modelling a wide range of electromagnetic problems. Structures considered include single and twin-slot antennas for millimetre-wave applications, monopole antennas on mobile handsets and chokes for the suppression of currents on coaxial cables. Memory efficient techniques were implemented for the split-field perfectly matched layer (PML) absorbing boundary condition. The frequency-domain far-field transformations were used for the calculation of far-field radiation patterns. Dipole, slot and mobile handset antenna benchmark problems verified the accuracy of the FDTD implementation. The application of slot antennas for millimetre-wave imaging arrays was investigated. An optimal feed network for an offset-fed single-slot antenna was designed for the X band with numerical and experimental results in excellent agreement. A twin-slot antenna structure reduced surface wave coupling by 7.6 dB in the substrate between coplanar waveguide-fed slot antenna elements in a planar array. The reduction of substrate surface waves for the twin-slot antenna allows for closer element spacings with less radiation pattern degradation in array applications. Suppression techniques for currents flowing on the exterior surface of coaxial cables were investigated. These include the use of ferrite beads and a quarter-wave sleeve balun. The frequency dependent behaviour of ferrite based chokes showed highly resonant effects which resulted in less than 5 dB of isolation at the resonant frequencies of the bead. An analysis of air-gaps between the ferrite bead and cable are shown to be extremely detrimental in the isolation characteristics of ferrite bead chokes. An air-gap of 0.5 mm can reduce the isolation effectiveness of a bead by 20 dB. The first rigorous analysis of a quarter-wave sleeve balun is presented, enabling an optimal choke design for maximum isolation. A standard 0.25[symbols] sleeve balun achieved 10.9 dB isolation with [symbols]=4, whereas a choke of optimal length 0.232[symbols] had an isolation of better than -20 dB. Several techniques for the measurement of antenna characteristics of battery powered handsets were compared and perturbation effects associated with the direct connection of a coaxial cable to a mobile handset was quantified. Significant perturbation in both return loss and radiation pattern can occur depending on cable location on the handset chassis. The effectiveness of ferrite chokes in any location was marginal. However, the application of an optimal quarter-wave sleeve balun in the centre of the largest plane of the handset, orthogonal to the primary polarisation resulted in minimal perturbation of both radiation patterns and return loss.