Artificial magnetic materials (AMMs) are a type of metamaterials which are engineered to exhibit desirable magnetic properties not found in nature. AMMs are realized by embedding electrically small metallic resonators aligned in parallel planes in a host dielectric medium. In the presence of a magnetic field, an electric current is induced on the inclusions leading to the emergence of an enhanced magnetic response inside the medium at the resonance frequency of the inclusions. AMMs with negative permeability are used to develop single negative, or double negative metamaterials. AMMs with enhanced positive permeability are used to provide magneto-dielectric materials at microwave or optical frequencies where the natural magnetic materials fail to work efficiently. Artificial magnetic materials have proliferating applications in microwave and optical frequency region. Such applications include inversely refracting the light beam, invisibility cloaking, ultra miniaturizing and frequency bandwidth enhancing low profile antennas, planar superlensing, super-sensitive sensing, decoupling proximal high profile antennas, and enhancing solar cells efficiency, among others. AMMs have unique enabling features that allow for these important applications. Fundamental limitations on the performance of artificial magnetic materials have been derived. The first limitation which depends on the generic model of permeability functions expresses that the frequency dispersion in an AMM is limited by the desired operational bandwidth. The other constraints are derived based on the geometrical limitations of inclusions. These limitations are calculated based on a circuit model. Therefore, a formulation for permeability and magnetic susceptibility of the media based on a circuit model is developed. The formulation is in terms of a geometrical parameter that represents the geometrical characteristics of the inclusions such as area, perimeter and curvature, and a physical parameter that represents the physical, structural and fabrication characteristics of the medium. The effect of the newly introduced parameters on the effective permeability of the medium and the magnetic loss tangent are studied. In addition, the constraints and relations are used to methodically design artificial magnetic material meeting specific operational requirements. A novel design methodology based on an introduced analytical formulation for artificial magnetic material with desired properties is implemented. The synthesis methodology is performed in an iterative four-step algorithm. In the first step, the feasibility of the design is tested to meet the fundamental constraints. In consecutive steps, the geometrical and physical factors which are attributed to the area and perimeter of the inclusion are synthesized and calculated. An updated range of the inclusion's area and perimeter is obtained through consecutive iterations. Finally, the outcome of the iterative procedure is checked for geometrical realizability. The strategy behind the design methodology is generic and can be applied to any adopted circuit based model for AMMs. Several generic geometries are introduced to realize any combination of geometrically realizable area and perimeter (s,l) pairs. A realizable geometry is referred to a contour that satisfies Dido's inequality. The generic geometries introduced here can be used to fabricate feasible AMMs. The novel generic geometries not only can be used to enhance magnetic properties, but also they can be configured to provide specific permeability with desired dispersion function over a certain frequency bandwidth with a maximum magnetic loss tangent. The proposed generic geometries are parametric contours with uncorrelated perimeter and area function. Geometries are configured by tuning parameters in order to possess specified perimeter and surface area. The produced contour is considered as the inclusion's shape. The inclusions are accordingly termed Rose curve resonators (RCRs), Corrugated rectangular resonators (CRRs) and Sine oval resonators (SORs). Moreover, the detailed characteristics of the RCR are studied. The RCRs are used as complementary resonators in design of the ground plane in a microstrip stop-band filter, and as the substrate in design of a miniaturized patch antenna. The performance of new designs is compared with the counterpart devices, and the advantages are discussed.

The concept for a novel new antenna design is presented and investigated for application to ground penetrating radar (GPR). The proposed new antenna design is called the shielded magnetic bowtie antenna (MBA). As the name suggests, it is predominately constructed from a bowtie-shaped volume of magnetic material that is fed from the centre of the structure by a small magnetic loop antenna. This thesis develops the magnetic antenna concept and investigates its potential for GPR predominately through numerical modelling. However, a significant part of the investigation concentrates on validating the numerical modelling technique developed to study the shielded MBA by comparing the results with measurements obtained from a scale model constructed to operate in the watertank antenna test facility, a controlled environment for GPR antenna research. The broadband properties required for GPR antennas are achieved uniquely with the shielded MBA design by a combination of the antenna shape being defined in terms of angles and an inherent magnetic loss mechanism within the antenna material structure. The design also affords an intrinsically placed antenna shield that has the potential for mitigating problems typically experienced with shielding electric dipole antennas. Antenna shielding is an important consideration for GPR antenna designers, especially given the recent US government (FCC) changes that restrict radiated energy emissions within the regulated spectrum used by GPR systems. In addition to providing the intended directional radiation properties, the magnetic antenna shield also provides an elegant solution for a low-loss wideband balun, allowing the antenna to be effectively fed from an unbalanced coaxial transmission line. Other important aspects of the proposed design are discussed in relation to the requirements for GPR antennas. Numerical models of the magnetic antenna concept show encouraging bandwidth results. For example, from a simple comparison with an equivalent sized electric bowtie antenna model, the effective gain bandwidth of the magnetic antenna is found to be at least 3-octaves compared to approximately 2-octaves for the electric bowtie. The shielded magnetic antenna achieves a gain of approximately 2 dB, compared to 5 dB for the unshielded electric bowtie antenna. However, it is noted that the magnetic antenna models contain significantly more loss compared to the electric bowtie model. The shielded MBA design emerged from a theoretical investigation of electrically small GPR antennas, given that the initial thesis objective was to investigate ways of improving low frequency GPR antennas. In general, GPR systems are operated with electric dipole antennas, such as the electric bowtie. Interestingly, the electrically small antenna investigation revealed that only the small magnetic loop (i.e., magnetic dipole) antenna can be constructed to approach, arbitrarily closely, the fundamental bandwidth limit for small antennas. This surprising and counter intuitive result is shown to be theoretically achievable with the use of magnetic materials. For the small loop antenna, energy stored within the antenna structure can be avoided by filling the antenna sphere with a perfect magnetic material. This theoretical argument is discussed and supported by numerically modelled results. The electrically small antenna investigation presented in this thesis extends to include the influence that proximity to a lossy dielectric half-space has, on improving the antenna impedance bandwidth. This investigation is of general interest for GPR; it is performed numerically and supported by measurements conducted on an experimental loop antenna situated at various heights above the ground. These results provide support for the hypothesis that a magnetic antenna may experience less influence from near-field changes in the dielectric properties of the ground compared to the equivalent sized electric field antenna.

В работе представлены результатыисследования метода, который позволяет увеличить полосу частот электрически малой антенны с помощью “нефостеровской цепи”на основе операционного усилителя. Были получены графики, которые позволяют оценить входное реактивное сопротивление и полосу частот электрически малой антенны с представленным методом расширения полосы частот. / The paper presents the results of a study of the method, which makes it possible to increase the frequency band of an electrically small antenna by means of a "Non-foster circuit"with operational amplifier. The graphs were obtain, which allow estimating the input reactance and the bandwidth of an electrically small antenna with the method of bandwidth extension represented.

В работе представлены результатыисследования метода, который позволяет увеличить полосу частот электрически малой антенны с помощью “нефостеровской цепи”.Также были представлены классические методы расширения полосы частот антенны с помощью индуктивности и колебательного контура, чтобы сравнить их эффективность с исследуемым методом. Были получены графики, которые позволяют оценить входное реактивное сопротивление и полосу частот электрически малой антенны со всеми представленными методами расширения полосы частот. / The paper presents the results of a study of the method, which makes it possible to increase the frequency band of an electrically small antenna by means of a "Non-foster circuit". Also, classical methods for extending the frequency band of the antenna with the help of inductance and a vibrational circuit were presented to compare their effectiveness with the method being studied.

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Characteristic modes (CMs) provide deep insight into the electromagnetic behaviour of any arbitrarily shaped conducting structure because the CMs are unique to the geometry of the object. We exploit this very fact by predicting a perhaps surprising number of important antenna metrics such as resonance frequency, radiation efficiency and antenna Q (bandwidth) without needing to specify a feeding location. In doing so, it is possible to define a collection of objective functions that can be used in an optimizer to shape-synthesize antennas without needing to define a feed location a priori. We denote this novel form of optimization “feedless” or “excitation-free” antenna shape synthesis. Fundamentally, we are allowing the electromagnetics to dictate how the antenna synthesis should proceed and are in no way imposing the physical constraints enforced by fixed feeding structures. This optimization technique is broadly applied to three major areas of antenna research: electrically small antennas, multi-band antennas and reflectarrays. Thus, the scope of applicability ranges from small antennas, to intermediate sizes and concludes with electrically large antenna designs, which is a testament to the broad applicability of characteristic mode theory. Another advantage of feedless electromagnetic shape synthesis is the ability to synthesize antennas whose desirable properties approach the fundamental limits imposed by electromagnetics. As an additional benefit, the feedless optimization technique is shown to have greater computational efficiency than traditional antenna optimization techniques.

Characteristic modes (CMs) provide deep insight into the electromagnetic behaviour of any arbitrarily shaped conducting structure because the CMs are unique to the geometry of the object. We exploit this very fact by predicting a perhaps surprising number of important antenna metrics such as resonance frequency, radiation efficiency and antenna Q (bandwidth) without needing to specify a feeding location. In doing so, it is possible to define a collection of objective functions that can be used in an optimizer to shape-synthesize antennas without needing to define a feed location a priori. We denote this novel form of optimization “feedless” or “excitation-free” antenna shape synthesis. Fundamentally, we are allowing the electromagnetics to dictate how the antenna synthesis should proceed and are in no way imposing the physical constraints enforced by fixed feeding structures. This optimization technique is broadly applied to three major areas of antenna research: electrically small antennas, multi-band antennas and reflectarrays. Thus, the scope of applicability ranges from small antennas, to intermediate sizes and concludes with electrically large antenna designs, which is a testament to the broad applicability of characteristic mode theory. Another advantage of feedless electromagnetic shape synthesis is the ability to synthesize antennas whose desirable properties approach the fundamental limits imposed by electromagnetics. As an additional benefit, the feedless optimization technique is shown to have greater computational efficiency than traditional antenna optimization techniques.

Ultra Wideband (UWB) communication has recently drawn considerable attention from academia and industry. This is mainly owing to the ultra high speeds and cognitive features it could offer. The employability of UWB in numerous areas including but not limited to Wireless Personal Area Networks, WPAN's, Body Area Networks, BAN's, radar and medical imaging etc. has opened several avenues of research and development. However, still there is a disagreement on the standardization of UWB. Two contesting radios for UWB are Multiband Orthogonal Frequency Division Multiplexing (MB-OFDM) and DS-UWB (Direct Sequence Ultra Wideband). As nearly all of the reported research on UWB hasbeen about a very narrow/specific area of the communication system, this thesis looks at the end-to-end performance of an MB-OFDM approach. The overall aim of this project has been to first focus on three different aspects i.e. interference, antenna and propagation aspects of an MB-OFDM system individually and then present a holistic or an end-to-end system analysis finally. In the first phase of the project the author investigated the performance of MB-OFDM system under the effect of his proposed generic or technology non-specific interference. Avoiding the conventional Gaussian approximation, the author has employed an advanced stochastic method. A total of two approaches have been presented in this phase of the project. The first approach is an indirect one which involves the Moment Generating Functions (MGF's) of the Signal-to-Interference-plus-Noise-Ratio (SINR) and the Probability Density Function (pdf) of the SINR to calculate the Average Probabilities of Error of an MB-OFDM system under the influence of proposed generic interference. This approach assumed a specific two-dimensional Poisson spatial/geometric placement of interferers around the victim MB-OFDM receiver. The second approach is a direct approach and extends the first approach by employing a wider class of generic interference. In the second phase of the work the author designed, simulated, prototyped and tested novel compact monopole planar antennas for UWB application. In this phase of the research, compact antennas for the UWB application are presented. These designs employ low-loss Rogers duroid substrates and are fed by Copla-nar Waveguides. The antennas have a proposed feed-line to the main radiating element transition region. This transition region is formed by a special step-generating function-set called the "Inverse Parabolic Step Sequence" or IPSS. These IPSS-based antennas are simulated, prototyped and then tested in the ane-choic chamber. An empirical approach, aimed to further miniaturize IPSS-based antennas, was also derived in this phase of the project. The empirical approach has been applied to derive the design of a further miniaturized antenna. More-over, an electrical miniaturization limit has been concluded for the IPSS-based antennas. The third phase of the project has investigated the effect of the indoor furnishing on the distribution of the elevation Angle-of-Arrival (AOA) of the rays at the receiver. Previously, constant distributions for the AOA of the rays in the elevation direction had been reported. This phase of the research has proposed that the AOA distribution is not fixed. It is established by the author that the indoor elevation AOA distributions depend on the discrete levels of furnishing. A joint time-angle-furnishing channel model is presented in this research phase. In addition, this phase of the thesis proposes two vectorial or any direction AOA distributions for the UWB indoor environments. Finally, the last phase of this thesis is presented. As stated earlier, the overall aim of the project has been to look at three individual aspects of an MB-OFDM system, initially, and then look at the holistic system, finally. Therefore, this final phase of the research presents an end-to-end MB-OFDM system analysis. The interference analysis of the first phase of the project is revisited to re-calculate the probability of bit error with realistic/measured path loss exponents which have been reported in the existing literature. In this method, Gaussian Quadrature Rule based approximations are computed for the average probability of bit error. Last but not the least, an end-to-end or comprehensive system equation/impulse response is presented. The proposed system equation covers more aspects of an indoor UWB system than reported in the existing literature.

Characteristic modes (CMs) provide deep insight into the electromagnetic behaviour of any arbitrarily shaped conducting structure because the CMs are unique to the geometry of the object. We exploit this very fact by predicting a perhaps surprising number of important antenna metrics such as resonance frequency, radiation efficiency and antenna Q (bandwidth) without needing to specify a feeding location. In doing so, it is possible to define a collection of objective functions that can be used in an optimizer to shape-synthesize antennas without needing to define a feed location a priori. We denote this novel form of optimization “feedless” or “excitation-free” antenna shape synthesis. Fundamentally, we are allowing the electromagnetics to dictate how the antenna synthesis should proceed and are in no way imposing the physical constraints enforced by fixed feeding structures. This optimization technique is broadly applied to three major areas of antenna research: electrically small antennas, multi-band antennas and reflectarrays. Thus, the scope of applicability ranges from small antennas, to intermediate sizes and concludes with electrically large antenna designs, which is a testament to the broad applicability of characteristic mode theory. Another advantage of feedless electromagnetic shape synthesis is the ability to synthesize antennas whose desirable properties approach the fundamental limits imposed by electromagnetics. As an additional benefit, the feedless optimization technique is shown to have greater computational efficiency than traditional antenna optimization techniques.