Wireless communication is part of our daily life in several applications, such as cell phones, wireless printers, sensors, etc. Each wireless device requires at least one antenna to communicate with other devices. In 2002, Federal Communications Commission (FCC) assigned a frequency spectrum from 3.1 GHz to 10.6 GHz for ultra-wideband communications. Several narrowband antennas require to cover the entire range. Unlike narrowband antennas, ultra-wideband antennas need to cover the wide frequency band. This research mainly focuses on physically small antenna designs. The first antenna discussed in this dissertation is a dual, triple trident antenna with dimensions 24 mm × 28 mm × 0.785 mm, which will operate from 3 GHz to 12.15 GHz [58]. The first antenna consists of six tridents symmetrical along the vertical direction. The second antenna design is a novel rectangular ring ultra-wideband antenna [59]. Large antennas operate for low frequency, and small antennas work for high frequency. The number of rings increased in wideband antenna to 9 from 4 to check the design methodology. The rectangular ring ultra-wideband antenna has dimensions 24 mm × 26 mm × 1.52 mm. This antenna operates from 3.12 GHz to 12.85 GHz. The third antenna design is an ultra-wideband dual square trident planar antenna. This antenna’s overall size is 26 mm × 24 mm × 1.56 mm [60]. This antenna has impedance bandwidth from 3.65 GHz to 12.50 GHz. The fourth antenna design is an ultra-wideband antenna with a band notch from 5.05 GHz to 5.9 GHz [61]. This antenna consists of two tridents and two split-ring resonators along the microstrip feed line. The overall size of this antenna 26 mm ×24 mm × 1.53mm. Simulations are carried out using the CST microwave studios® to analyze the antenna performance. Experiments are conducted to verify the simulated results using vector network analyzers for impedance and anechoic antenna chamber for radiation characteristics of the antenna. All four antennas are excellent for the wireless device due to their compact size and planar designs.

In the future, space solar power transmission and wireless power transmission will play an important role in gathering clean and infinite energy from space. The rectenna, i.e., a rectifying circuit combined with an antenna, is one of the most important components in the wireless power transmission system. To obtain high power and high output voltage, the use of a large rectenna array is necessary. Many novel rectennas and rectenna arrays for microwave and millimeter-wave wireless power transmission have been developed. Unlike the traditional rectifying circuit using a single diode, dual diodes are used to double the DC output voltage with the same circuit layout dimensions. The rectenna components are then combined to form rectenna arrays using different interconnections. The rectennas and the arrays are analyzed by using a linear circuit model. Furthermore, to precisely align the mainbeams of the transmitter and the receiver, a retrodirective array is developed to maintain high efficiency. The retrodirective array is able to track the incident wave and resend the signal to where it came from without any prior known information of the source location. The ultra-wideband radio has become one of the most important communication systems because of demand for high data-rate transmission. Hence, ultra-wideband antennas have received much attention in mobile wireless communications. Planar monopole ultra-wideband antennas for UHF, microwave, and millimeter-wave bands are developed, with many advantages such as simple structure, low cost, light weight, and ease of fabrication. Due to the planar structures, the ultra-wideband antennas can be easily integrated with other circuits. On the other hand, with an ultra-wide bandwidth, source power can be transmitted at different frequencies dependent on power availability. Furthermore, the ultra-wideband antenna can potentially handle wireless power transmission and data communications simultaneously. The technologies developed can also be applied to dual-frequency or the multi-frequency antennas. In this dissertation, many new rectenna arrays, retrodirective rectenna arrays, and ultra-wideband antennas are presented for microwave and millimeter-wave applications. The technologies are not only very useful for wireless power transmission and communication systems, but also they could have many applications in future radar, surveillance, and remote sensing systems.

Acquisition of ultra-wideband signals by means of array antennas requires essentially frequency-independent radiation characteristics over the entire bandwidth of the signal in order to avoid distortions. Factors contributing to bandwidth limitation of arrays include array factor, radiation characteristics of the array element, and inter-element mutual coupling. Strictly speaking, distortion-free transmission or reception of ultra-wideband signals can be maintained if the magnitude of the radiated field of the array remains constant while its phase varies linearly with frequency over the bandwidth of interest. The existing wideband-array synthesis methods do not account for all factors affecting the array bandwidth and are often limited to considering the array factor and not the total field of the array in the synthesis process. The goal of this study is to present an ultra-wideband array synthesis technique taking into account all frequency-dependent properties, including array total pattern, phase of the total radiated field, element field, element input impedance, and inter-element mutual coupling. The proposed array synthesis technique is based on the utilization of frequency-adaptive element excitations in conjunction with expressing the total radiated field of the array as a complex Fourier series. Using the proposed method, element excitation currents required for achieving a desired radiation pattern, while compensating for frequency variations of the element radiation characteristics and the inter-element mutual coupling, are calculated. An important consideration in the proposed ultra-wideband array design is that the "phase bandwidth", defined as the frequency range over which the phase of the total radiated field of the array varies linearly with frequency, is taken into account as a design requirement in the synthesis process. Design examples of linear arrays with desired radiation patterns that are expected to remain unchanged over the bandwidth of interest are presented and simulated. Two example arrays, one with a wire dipole as its element and another using an elliptically-shaped disc dipole as the element are studied. Simulation results for far-field patterns, magnitude and phase characteristics, and other performance criteria such as side-lobe level and scanning range are presented. Synthesis of two-dimensional planar arrays is carried out by employing the formulations developed for linear arrays but generalized to accommodate the geometry of planar rectangular arrays. As example designs, planar arrays with wire dipoles and elliptical-shaped disc dipoles are studied. The simulation results indicate that synthesis of ultra-wideband arrays can be accomplished successfully using the technique presented in this work. The proposed technique is robust and comprehensive, nonetheless it is understood that the achieved performance of a synthesized array and how closely the desired performance is met also depends on some of the choices the array designer makes and other constraints, such as number of elements, type of element, size, and ultimately cost. / Ph. D.

This thesis presents a novel antenna structure that satisfies the challenging requirements of an air coupled high speed ground penetrating radar (GPR). The desired GPR system is to achieve high spatial resolution and accurate inspection results while scanning at relatively high speed for highway pavement and bridge deck inspection. This work utilizes the Ultra Wide Band (UWB) antenna design to achieve both physical and electrical requirements imposed. The design procedure starts with a short survey to discuss typical UWB antennas used for GPR applications, and various tradeoffs of each type specifically when used for Air Coupled GPR applications. Our structure anatomy is presented, followed by a theory introduction that mainly focuses on achieving good impedance matching throughout the proposed antenna structure. A proof-of-concept MATLAB model is created to evaluate the preliminary physical dimensions that can achieve minimum reflections at antenna's feed point. These dimensions are then used in SolidWorks to create a 3D model that is imported later in HFSS to obtain accurate electromagnetic characteristics. Furthermore, fine tunings are performed to the antenna structure to optimize both gain and impedance matching. The SolidWorks 3-D structural model is finally used for antenna fabrication. The measurements recorded from the field experiments using the prototypes manufactured are compared to the simulation results confirming our initial findings. Both measurements and simulation results demonstrated very small reflection loss across the 700 MHz ~ 6 GHz frequency band with a very high directed gain and radiation efficiency.

Les besoins techniques et opérationnels des porteurs navals, terrestres et aériens conduisent à la conception et à l'implantation d'un nombre de plus en plus élevé d'antennes dédiées aux communications. Parallèlement, les matériaux composites sont utilisés depuis de nombreuses décennies dans les panneaux structuraux de ces porteurs en raison de leurs qualités naturelles (légèreté, performances mécaniques élevées, insensibilité à la corrosion…). L'objet de ce manuscrit concerne l'étude et le développement de matériaux composites pour des applications antennaires en hyperfréquences. Après un recensement exhaustif des caractéristiques diélectriques des différents éléments constitutifs de ces matériaux composites, la caractérisation diélectrique des matériaux composites fabriqués au Laboratoire a été réalisée via deux méthodes distinctes dans deux bandes de fréquence différentes. Parallèlement, la caractérisation électrique des tissus à base de fibres de carbone a permis d'évaluer leur possible utilisation dans la fabrication des éléments rayonnants. Dans un premier temps, deux topologies antennaires « tout composite » de géométrie carrée à base de tissus de fibres de carbone, de fibres de verre et de résine (polyester ou époxy) ont été conçues, fabriquées et caractérisées. Leurs performances similaires à celles d'antennes métalliques de référence démontrent tout l'intérêt de l'utilisation des matériaux composites en hyperfréquences. Puis, trois topologies antennaires ultra large bande en matériaux « tout composite » ont été développées spécifiquement dans le cadre du projet FUI SAMCOM (/Systèmes Antennaires en Matériaux COMposites/). La première de type Rugby-Ball couvre une octave et demi avec un gain positif et un encombrement limité à λ/4 x λ/4 x λ/10 (longueur x largeur x hauteur). La seconde configuration volumique de type dipôle et d'encombrement λ/3 x λ/3 x λ/10 couvre deux octaves et demi avec un gain toujours positif. Enfin, la troisième de structure planaire a été développée spécifiquement pour la réception de la Télévision Numérique Terrestre (TNT) et sera, à terme, intégrée dans un panneau structural d'un véhicule. / The technical and operational requirements of naval, terrestrial and aerial vehicles lead to the design and installation of a great number of antennas for communications. At the same time, composite materials have been used for many decades in structural panels of vehicles for their intrinsic qualities (lightness, high mechanical performance, insensitivity to corrosion ...). The purpose of this manuscript is the study and engineering of composite materials for antenna applications at microwaves. After an exhaustive survey of the dielectric characteristics of the various elements of composite materials, dielectric characterization of composite materials manufactured in the Laboratory was carried out using two different methods in two different frequency bands. Meanwhile, an analysis of their conductive characteristics allows carbon-fiber tissues to be used in the design of radiating elements. First, two "full-composite" square shaped antennas based on carbon-fiber tissues, glass-fiber tissues and polyester or epoxy resin have been developed, fabricated and measured. Their performance, similar to that of reference metal antennas demonstrates their relevance for microwave applications. Then, three different topologies of ultra wideband "full-composite" antennas have been specifically developed for the SAMCOM (/Antenna Systems in COMposite Materials)/ FUI project. The first, a Rugby-Ball shaped antenna, has one octave and a half of bandwidth with a positive gain and λ/4 x λ/4 x λ/10 dimensions (length x width x height). The second, a 3D dipole antenna with λ/3 x λ/3 x λ/10 dimensions, has two octaves and a half of bandwidth also with a positive gain. At last, the third antenna with a planar structure has been specifically developed for the reception of digital terrestrial television (DTT) and will be, at the end, integrated into a structural panel of a terrestrial vehicle.

The research of this thesis is on the mobile TV antenna designs. There are three antenna designs proposed in this thesis. The first two designs are for portable TV sets. They are different from the traditional straight monopole antenna because the two proposed designs can be built-in with the portable TV set. The third one is for laptop applications. It can be stored inside a laptop when the antenna is not in use, and can be pulled out of the laptop when in operation. Thus the proposed antenna will not affect the appearance of the laptop.

Ultra-wideband (UWB) antennas are one of the most important elements for UWB systems. With the release of the 3.1 - 10.6 GHz band, applications for short-range and high-bandwidth handheld devices are primary research areas in UWB systems. Therefore, the realization of UWB antennas in printed-circuit technologies within relatively small substrate areas is of primary importance. This thesis focuses on the design of a new UWB antenna based on coplanar technology. Compared with microstrip circuitry, coplanar technology achieves easier fabrication and wider antenna bandwidth. Two professional full-wave field solver software packages, HFSS and MEFiSTo-3D, are used as analysis tools to obtain antenna performances. A new printed-circuit antenna in coplanar technology for UWB systems is introduced. The frequency of operation is 3.1 GHz to 10.6 GHz with a VSWR < 2. Nearly omni-directional characteristics in vertical polarization are demonstrated at selected frequencies. Relatively good group delay characteristics are obtained and compare well with other published UWB antenna designs.

Yes / A compact planar monopole antenna is proposed for ultra-wideband applications. The antenna has a microstrip line feed and band-rejected characteristics and consists of a ring patch and partial ground plane with a defective ground structure of rectangular shape. An annular strip is etched above the radiating element and two slots, one C-shaped and one arc-shaped, are embedded in the radiating patch. The proposed antenna has been optimized using bio-inspired algorithms, namely Particle Swarm Optimization and the Firefly Algorithm, based on a new software algorithm (Antenna Optimizer). Multi-objective optimization achieves rejection bands at 3.3 to 3.7 GHz for WiMAX, 5.15 to 5.825 GHz for the 802.11a WLAN system or HIPERLAN/2, and 7.25 to 7.745 GHz for C-band satellite communication systems. Validated results show wideband performance from 2.7 to 10.6 GHz with S11 ˂ -10 dB. The antenna has compact dimensions of 28 × 30 mm2. The radiation pattern is comparatively stable across the operating band with a relatively stable gain except in the notched bands. / This work was supported in part by the United Kingdom Engineering and Physical Science Research Council (EPSRC) under Grant EP/E022936A, TSB UK under grant application KTP008734 and the Iraqi Ministry of Higher Education and Scientific Research.

As ubiquitous wireless communication becomes part of life, the demand on antenna miniaturization and interference reduction becomes more extreme. However, antenna size and performance are limited by radiation physics, not technology. In order to understand antenna radiation and energy storage mechanisms, classical and alternative viewpoints of radiation are discussed. Unlike the common sense of classical antenna radiation, it is shown that the entire antenna fields contribute to both radiation and energy storage with varying total energy velocity during the radiation process. These observations were obtained through investigating impedance, power, the Poynting vector, and energy velocity of a radiating antenna. Antenna transfer functions were investigated to understand the real-world challenges in antenna design and overall performance. An extended model, using both the singularity expansion method and spherical mode decomposition, is introduced to analyze the characteristics of various antenna types including resonant, frequency-independent, and ultra-wideband antennas. It is shown that the extended model is useful to understand real-world antennas. Observations from antenna radiation physics and transfer function modeling lead to both corrections and extension of the classical fundamental-limit theory on antenna size. Both field and circuit viewpoints of the corrected limit theory are presented. The corrected theory is extended for multi-mode excitation cases and also for ultra-wideband and frequency-independent antennas. Further investigation on the fundamental-limit theory provides new innovations, including a low-Q antenna design approach that reduces antenna interference issues and a generalized approach for designing an antenna close to the theoretical-size limit. Design examples applying these new approaches with simulations and measurements are presented. The extended limit theory and developed antenna design approaches will find many applications to optimize compact antenna solutions with reduced near-field interactions. / Ph. D.

Yes / In this article, a novel uniplanar ultra‐wideband (UWB) stop frequency selective surface (FSS) was miniaturized to maximize the gain of a compact UWB monopole antenna for microwave imaging applications. The single‐plane FSS unit cell size was only 0.095λ × 0.095λ for a lower‐operating frequency had been introduced, which was miniaturized by combining a square‐loop with a cross‐dipole on FR4 substrate. The proposed hexagonal antenna was printed on FR4 substrate with coplanar waveguide feed, which was further backed at 21.6 mm by 3 × 3 FSS array. The unit cell was modeled with an equivalent circuit, while the measured characteristics of fabricated FSS array and the antenna prototypes were validated with the simulation outcomes. The FSS displayed transmission magnitude below −10 dB and linear reflection phase over the bandwidth of 2.6 to 11.1 GHz. The proposed antenna prototype achieved excellent gain improvement about 3.5 dBi, unidirectional radiation, and bandwidth of 3.8 to 10.6 GHz. Exceptional agreements were observed between the simulation and the measured outcomes. Hence, a new UWB baggage scanner system was developed to assess the short distance imaging of simulated small metallic objects in handbag model. The system based on the proposed antenna displayed a higher resolution image than the antenna without FSS.