The main goal of this research is to develop a new type of antenna, called reconfigurable antenna, which can replace multiple antennas required to enhance the effectiveness of a robust communication system. A recongurable antenna integrated with switching elements can dynamically change its properties, namely, frequency of operation, radiation pattern (the three-dimensional coverage of antenna), and polarization (the electrical orientation of the antenna). Depending on the requirement, a single antenna can function as multiple an- tennas, therefore, the name Multi-functional Recongurable Antenna (MRA). United States (US) Public Safety (PS) responders (police, re-ghters, emergency medical services, etc.) can effectively respond to human-made or natural catastrophies if they are equipped with robust communication systems supported by MRA. Wireless implementations of computer accessories (wireless HDMI, wireless storage to external hard-drive, etc.) that require high speed data communication are supported by 60 GHz communications. Equipping these devices with MRA could further increase the speed of communication, thereby resulting in a robust communication. In this work, pin-diodes and Micro Electro Mechanical Switches (MEMS) are integrated on the MRAs to reconfigure (dynamically change) its properties namely frequency and radiation pattern. An MRA capable of operating over 220, 470, 800, 4900 MHz PS bands is designed, manufactured, tested, and characterized. Another MRA capable of changing its radiation pattern over 4.94-4.99 GHz band is designed, manufactured, tested, and characterized. The design of radiation pattern recongurable MRA and Multi-functional Reconfigurable Antenna Array (MRAA) for 60 GHz communication is also accomplished. The MRAA is designed in order to enhance the MRA's capability to receive or transmit more power.

No description available.

A pattern-reconfigurable, low-profile, efficient, electrically small, near-field resonant parasitic (NFRP), Huygens source antenna is presented. The design incorporates both electric and magnetic NFRP elements. The electric ones are made reconfigurable by the inclusion of a set of p-i-n diodes. By arranging these electric and magnetic NFRP elements properly, a set of three Huygens sources are attained, each covering a 120 degrees sector. Pattern reconfigurability is obtained by switching the diodes on or off; it encompasses the entire 360 degrees azimuth range. A prototype was fabricated and tested. The numerical and experimental studies are in good agreement. The experimental results indicate that in each of its instantaneous states at f(0) = 1.564 GHz, the antenna provides uniform peak realized gains, front-toback ratios, and radiation efficiencies, respectively, as high as 3.55 dBi, 17.5 dB, and 84.9%, even though it is electrically small: ka = 0.92, and low profile: 0.05 lambda(0).

Le plasma est un gaz ionisé qui possède des caractéristiques physiques intéressantes dans le domaine des hyperfréquences. En simplifiant, on peut le caractériser comme un milieu diélectrique dispersif dont la permittivité est fonction de deux paramètres : la pulsation plasma (wp) et la fréquence de collision électron-neutre (Vp). En pratique, ces paramètres dépendent principalement de la densité électronique du gaz et de sa pression. Ainsi, en contrôlant les caractéristiques du plasma, on contrôle sa permittivité diélectrique, ce qui permet d’envisager son application dans le domaine de la reconfigurabilité en hyperfréquence.Parmi les topologies pouvant générer une décharge plasma, nous nous sommes focalisés sur l’utilisation de topologies récentes, à savoir les microdécharges plasma. Ces microdécharges sont intéressantes de par leur facilité d’intégration dans un dispositif RF : petite taille, stabilité, température proche de la température ambiante et perspectives d’utilisation à plus haute pression, voire à la pression atmosphérique.Devant la difficulté de modéliser précisément l’effet du plasma sur une onde guidée, une approche expérimentale a été privilégiée. Deux dispositifs de mesure ont ainsi été conçus pour caractériser cette interaction : une ligne de transmission microruban classique et une inversée intégrant une microdécharge en leurs centres. Grâce au protocole expérimental mis en œuvre, les paramètres S de la ligne de transmission sont obtenus et comparés à ceux des lignes sans plasma dans une large gamme paramétrique, qu’il s’agisse de la pression du gaz, de la fréquence ou encore du courant injecté à la décharge. Les résultats obtenus montrent deux phénomènes particulièrement intéressants: un déphasage de l’onde électromagnétique en présence de la décharge plasma et / ou une absorption importante de la puissance par la décharge.Deux dispositifs antennaires ont finalement été conçus en exploitant ces résultats. Le premier est une antenne imprimée accordable en fréquence dans une plage de l’ordre du pourcent, grâce à une décharge plasma contrôlée.Le plasma modifie alors la constante diélectrique entre les deux conducteurs constitutifs de l’antenne. Le second dispositif est une antenne anneau imprimée qui peut protéger son récepteur d’une attaque microondes de forte puissance. Ainsi, lorsqu’un champ incident dépasse un seuil prédéfini, réglable dans une certaine mesure par une tension continue externe, une décharge plasma apparaît au sein de l’élément rayonnant. Elle crée alors de la désadaptation et de l’absorption qui limitent de façon non linéaire la puissance restituée à l’accès. / Plasma is an ionized gas with physical characteristics that are of interest to the microwave domain. To simplify, we can characterize it as a dispersive medium whose dielectric permittivity depends on two parameters :the plasma pulsation wp and the electron-neutral collision frequency Vp. These two parameters depend mainly on the electron density of the gas and its pressure. If we can control the characteristics of the plasma, we can also control its dielectric permittivity, which allows us to consider the plasma for applications in the field of microwave reconfigurability.Among the structures that can generate a plasma discharge, we have focused on the use of recent topologies,known as plasma microdischarges. These microdischarges are of interest because of the possibility of easily integrating them into a RF device : small size, stability, temperature near room temperature and potential use at high pressures, including at atmospheric pressure.Given the difficulties in accurately modelling the effects of the plasma on a guided wave, an experimental approachwas preferred. Two measuring devices have been designed to characterize this interaction : a conventional microstrip transmission line and an inverted microstrip transmisison line, both including a microdischarge in their centers. With this experimental characterization, the S-parameters of the transmission line with the plasma are obtained and compared to those without plasma as a function of a wide range of parameters, such as gas pressure,frequency and current injected into the discharge.The results show two particularly interesting phenomena : a phase shift of the electromagnetic wave in presence of the plasma discharge and/or an important absorption of the incident power by the discharge. Two devices have been designed to exploit these results. The first is a frequency tunable microstrip patch antenna over a range of the order of one percent. In that case, the plasma changes the dielectric constant between the two conductors of the antenna. The second is a microstrip ring patch antenna that can protect the receiver from a high-power microwave (HPM) attack. When an incident electric field exceeds an adjustable preset threshold (tuned by an external DCvoltage source), a plasma discharge appears in the radiating element. The plasma then creates a mismatch and an absorption effect that limits, in a non-linear way, the received power at its input.

Nous étudions la mise en oeuvre d ‘antenne à balayage électronique dédiés aux applications de communications par satellite géostationnaire. Les structures développées sont adaptées pour être embarquées dans un avion ou un train. L'architecture de l'antenne développée est constituée d’un double réseau linéaire dans deux dimmensions transverses. Le balayage dans chaque réseau linéaire est assuré par des lignes coplanaires à métamateriaux contrôlées par varactor. Nous porposons de nouvelles méthodes de caracterisation des discontinuités en ligne coplanaire pour la conception de la ligne. De plus, un système de prélèvement d'énergie a dû être conçu afin d'alimenter des éléments rayonnants et testé avec différentes antennes patch. Enfin, nous envisageons la co-intégration des structures rayonnantes et des lignes CRLH ainsi que le contrôle électronique par les diodes. / We are studying the implementation of 'Scanning Antenna dedicated to the applications of satellite communications geostationary. The structures developed are suitable for to be on board an airplane or a train. The architecture of the antenna developed consists of a double linear network in two transverse dimmensions. The scan in each network is provided by the lines coplanar to metamaterials controlled by varactor. We porposons of new methods characterization of discontinuities coplanar online for the line design. In addition, a energy harvesting system has be designed to feed radiating elements and tested with patch different antennas. Finally, we are considering co-integration radiating structures and CRLH lines as well as control electronic by the diodes.

This dissertation demonstrates the design of reversibly self-morphing novel liquid crystalline elastomer (LCE) antennas that can dynamically change electromagnetic performance in response to temperature. This change in performance can be achieved by programming the shape change of stimuli-responsive (i.e., temperature-responsive) LCEs, and using these materials as substrates for reconfigurable antennas. Existing reconfigurable antennas rely on external circuitry such as Micro-Electro-Mechanical-Systems (MEMS) switches, pin diodes, and shape memory alloys (SMAs) to reconfigure their performance. Antennas using MEMS or diodes exhibit low efficiency due to the losses from these components. Also, antennas based on SMAs can change their performance only once as SMAs response to the stimuli and is not reversible. Flexible electronics are capable of morphing from one shape to another using various techniques, such as liquid metals, hydrogels, and shape memory polymers. LCE antennas can reconfigure their electromagnetic performance, (e.g., frequency of operation, polarization, and radiation pattern) and enable passive (i.e., battery-less) temperature sensing and monitoring applications, such as passive radio frequency identification device (RFID) sensing tags. Limited previous work has been performed on shape-changing antenna structures based on LCEs. To date, self-morphing flexible electronics, including antennas, which rely on stimuli-responsive LCEs that reversibly change shape in response to temperature changes, have not been previously explored. Here, LCE antennas will be studied and developed. Also, the metallization of LCEs with different metal conductors and their fabrication process, by either electron beam (E-Beam) evaporation or optical gluing of the metal film will be observed. The LCE material can have a significant impact on sensing applications due to its reversible actuation that can enable a sensor to work repeatedly. This interdisciplinary research (material polymer science and electrical engineering) is expected to contribute to the development of morphing electronics, including sensors, passive antennas, arrays, and frequency selective surfaces (FSS).

This thesis presents the design, fabrication, and measurement of tunable frequency microstrip antennas using RF MEMS (Microelectromechanical Systems) technology. The integration of RF MEMS components with radiators enable to implement tunable systems due to the adjustable characteristics of RF MEMS components. In the frame of this thesis, different types of structures have been investigated and designed. The first structure consists of a microstrip patch antenna which is loaded with a microstrip stub whose length is controlled by RF MEMS switches. In the other structure, the length of a microstrip patch antenna is changed by connecting a metal plate using RF MEMS switches. The third structure is composed of a microstrip patch antenna and a microstrip stub on which RF MEMS variable capacitors are placed periodically to control the resonant frequency. In order to maintain an easier integration with RF MEMS capacitors, another structure consisting of a microstrip patch antenna and a coplanar waveguide (CPW) stub which is loaded with variable RF MEMS capacitors is designed. The final structure is a dual frequency CPW-fed rectangular slot antenna whose resonant frequencies are shifted by RF MEMS variable capacitors placed on a short circuited stub inserted inwards the antenna. The fabrication of CPW-fed rectangular slot antenna is completed in the MEMS fabrication facilities of METU using RF MEMS process based on electroforming on glass substrate. The measurement results show that RF MEMS components might be a proper solution to obtain tunable frequency antenna structures.

abstract: Flexibility, reconfigurability and wearability technologies for antenna designs are presented, investigated and merged in this work. Prior to the design of these radiating elements, a study is conducted on several flexible substrates and how to fabricate flexible devices. Furthermore, the integration of active devices into the flexible substrates is also investigated. A new approach of designing inkjet-printed flexible reconfigurable antennas, based on the concept of printed slot elements, is proposed. An alternate technique to reconfigure the folded slot antenna is also reported. The proposed radiator works for both Wireless Local Area Network (WLAN) and Worldwide Interoperability for Microwave Access (WiMAX) applications. The flexible reconfigurable antenna is also redesigned to resonate at both (2.4/5.2 GHz) for WLAN devices and its Multiple-Input Multiple-Output (MIMO) configuration is reported. Two orthogonal elements are used to form the MIMO antenna system for better isolation. The wearability of the proposed flexible reconfigurable radiator is also discussed. Since wearable antennas operate close to the human body, which is considered as a lossy tissue, an isolation between the radiating elements and human body is required to improve the radiation characteristics and to reduce the Specific Absorption Rate (SAR). The proposed antenna is redesigned on an Artificial Magnetic Conductor (AMC) surface that also functions as a ground plane to isolate the radiator from the human body. To examine its performance as a body-worn device, it is measured at different positions on the human body. Furthermore, simulations show that the SAR level is reduced when using the AMC surface. The proposed wearable antenna works for both Wireless Body Area Network (WBAN) and WiMAX body-worn wireless devices. Electromagnetic bandgap (EBG) structures are used to suppress surface wave propagation in printed antennas. However, due to the presence of vias, not all of them can be utilized in flexible radiators. Thus, a Perforated High Impedance Surface (PHIS) is proposed which suppresses the surface waves without the need of vias, and it also serves as a ground plane for flexible antennas. The surface wave suppression and the antenna applications of the proposed PHIS surface are discussed. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2017

In recent years, multi-functional reconfigurable antennas (MRA) has attracted much attention in wireless communication. The reconfigurable antenna can adapt itself with changing system conditions, and it can provide different multi-functionalities which can give better system performances. Instead of using multiple antennas, a single reconfigurable antenna can provide the same performance and occupy less space. By using the parasitic layer technique, an antenna can be turned into a reconfigurable antenna. The main objective of this thesis is to study radiation pattern reconfiguration of the horn antenna by using the parasitic layer concept. The MRA consists of a single horn, dielectric loaded truncated pyramid (DLTP), and the parasitic layer. The antenna that is chosen in this thesis is the horn antenna because it provides high directivity. DLTP is used for magnification purpose. The results show that three modes of operations that provide better performances compared to the single horn antenna are achieved.

The reconfigurable aperture (RECAP) is a reconfigurable antenna consisting of a dense array of electronically controlled elements, which can be manipulated to support many antenna functions within a single architecture. RECAPs are explored herein as an enabling technology for future software defined and cognitive radio architectures, as well as compact wireless devices supporting many bands and services. First, the concept of a parasitic RECAP is developed and analyzed for various communication applications. This begins with the analysis of existing RECAP topologies (e.g. planar and parasitic) using a hybrid method combining full wave simulations and network analysis. Next, a performance versus complexity analysis is performed to assess the use of a parasitic RECAP for the most critical communications functions: pattern synthesis, MIMO communications and physical-layer wireless security. To verify simulation results, a prototype parasitic RECAP is also built and deployed in real propagation environments. Given the potential of adaptive and reconfigurable architectures for providing enhanced security, an idealized reconfigurable antenna is analyzed, resulting in the concept of secure array synthesis. The objective is to find optimal array beamforming for secure communication in the presence of a passive eavesdropper in a static line-of-sight (LOS) channel. The method is then extended to the case of multipath propagation environments. The problem is solved by casting it into the form of a semi-definite program, which can be solved with convex optimization. The method is general and can be applied to an arbitrary array topology with or without antenna mutual-coupling. Due to complexity of the problem, initial attention has been restricted to idealized reconfigurable antennas (smart antennas), where excitation amplitude and phase at each element can be controlled independently. Lastly, reconfigurable antennas are investigated as a solution to support the emerging application of over-the-air (OTA) testing in a low-cost and compact way, resulting in the concept of the reconfigurable over-the-air chamber (ROTAC). First, an idealized two-dimensional ROTAC is analyzed, revealing that the fading distribution, spatial correlation, frequency selectivity, and multipath angular spectrum can be controlled by proper specification of the random loads. Later, a prototype of ROTAC is built to study the fading statistics and angular characteristics of the multipath fields inside a practical chamber.