Cette thèse s’intéresse à la conception d’antennes ultra large bande reconfigurables. Cette étude a été motivée par le souhait de regrouper l’ensemble des antennes d’observation présentes sur les satellites en un panneau rayonnant unique afin de pouvoir réduire la taille de ces derniers. Les travaux présentés dans ce mémoire sont donc principalement axés sur la conception d’antennes spirales et sur les améliorations qui peuvent leur être apportées. Ainsi, une nouvelle topologie d’antenne spirale carrée reconfigurable en un réseau de quatre antennes spirales carrées plus petites sur la même ouverture rayonnante est exposée. Cette reconfiguration permet d’augmenter l’efficacité de surface de la structure tout en offrant de nouvelles possibilités d’utilisation à l’antenne et en améliorant ses performances. Les caractéristiques et les performances des deux configurations en états figés sont détaillées. Les maquettes réalisées et les résultats de mesure sont également présentés afin de valider le fonctionnement de l’antenne. Ensuite, différentes améliorations de cette structure sont présentées ainsi qu’une application possible. Enfin, une solution permettant d’améliorer le fonctionnement des antennes spirales imprimées au-dessus d’un plan de masse est décrite. En effet, cette solution permet de supprimer un nul de rayonnement lorsque l’antenne se situe à une demi-longueur d’onde du plan de masse. Sa bande passante d’utilisation peut ainsi être potentiellement doublée sans perdre la moitié de l’énergie comme avec l’utilisation d’absorbants. Cette technique consiste à ajouter un élément rayonnant parasite au-dessus de l’antenne. Cet élément est excité par couplage à l’antenne spirale et rayonne à la fréquence du nul de rayonnement. Cet élément étant faible bande, il ne dégrade pas le fonctionnement de l’antenne aux autres fréquences de la bande passante. Une structure utilisant ce concept a été réalisée afin de valider son fonctionnement. / This thesis focuses on the design of ultrawideband reconfigurable antennas. The objective of this study is to integrate all the antennas of observation on satellites into a single radiating panel and make it reconfigurable. Works presented in this document are focused on the design of spiral antennas and on their possible improvements. Thereby, a new topology of square spiral antenna reconfigurable into an array of four smaller square spiral antennas is shown. This reconfiguration allows increasing the surface efficiency of the structure while offering new possibilities of utilization to the antenna and improving its performance. Characteristics and performance of both configurations in frozen states are presented. Breadboards and measurements are also presented in order to validate the functioning of the antenna. Then, several improvements of this structure are studied and a possible application. Finally, a solution for improving the functioning of spiral antennas printed over a metallic ground plane is presented. This solution permits to remove a null of radiation when the distance between the antenna and the ground plane is a multiple of the half wavelength. In this way, its bandwidth can be doubled without losing the half of the energy like with absorbers. This technique consists in adding a parasitic radiating element over the antenna. This element is fed by coupling to the spiral antenna and radiates at the frequency of the null of radiation. This element is narrowband, so antenna performance remains unchanged at the other frequencies of the bandwidth. A structure using this concept has been made in order to validate its functioning.

This work details the design and fabrication of an ultra-wideband periodic spiral antenna (PSA) with a notch filter embedded directly into the radiating aperture. Prototype fabrication of the PSA reveals long assembly time due to forming the antenna element, therefore modifications are made to allow fabricating the antenna elements on a thin, flexible, Polyimide substrate. A transmission line model is develop to support the updated configuration of the antenna elements. In addition, a symmetric spurline filter is integrated into the arms of the spiral antenna in order to address the common problem of interference in ultra-wideband systems. For the first time, a placement study is conducted to show the optimal location of the filter as a function of frequency. The presented transmission line model demonstrates the ability to decouple the design of the filter and antenna by being able to predict the resonant frequency and achieved rejection after integration of the two. Measured results show a gain rejection of 21 dB along with the ability to tune the resonance of the filter from 1.1 – 2.7 GHz using a lumped capacitor. For high power applications, thermal measurements are conducted, and for the first time, thermal profiles along the top of the antenna are used to show the radiation bands in a spiral antenna. Power tests are successfully conducted up to 40 W across the entire operational bandwidth and up to 60 W for 2 GHz and below. At these elevated power levels, a large voltage is generated across the lumped capacitor used to tune the resonance of the spurline filter; this issue is addressed through the development of a capacitive wedge that is overlapped on top of the spurline stub, which increases the voltage handling to 2,756 V. Measured results reveal a reduced tuning range compared to using lumped capacitors and a gain rejection of greater than 10 dB for all configurations.

Historical, well developed, procedures for RF design have minimal emphasis on exploring the third dimension due to the difficulty of fabrication. Recent material advancements applicable to 3D printing have brought about low-loss thermoplastics with excellent mechanical properties. Research into depositing conductive inks onto arbitrary 3D shapes has achieved resolutions better than 50 μm with conductivity values approaching that of copper cladding. The advancements in additive manufacturing have improved reliability and repeatability of three dimensional designs while decreasing fabrication time. With this design approach other considerations, such as stability and strength, can be concentrated on during the structure design to realize new shapes. The next step in the future of RF research will encompass designing and further understanding the benefits and consequences of using all three dimensions. This could include meandering an antenna element around other electronic components to make the overall package size smaller or integrating an antenna array into a wing. The design and analysis of the periodic spiral antenna (PSA) takes a look at a specific case of full volume utilization. In this application meandering in the z-dimension allowed the design to become smaller and more efficient than what is achievable with planar methods. This thesis will go into detail on the characterization of the periodic spiral antenna. To exemplify the benefits of meandering in the z-dimension a loop antenna is presented and benchmarked against other miniaturization techniques. Measured results of two different PSA models are presented and remarks on improving fabrication are given. When an antenna is used as a transmitter incident power will cause thermal generation so a study was conducted to understand how material properties can govern the amount of heat generated.

This thesis presents the designs of Ultra-wideband (UWB) monopole antennas, textile monopole antennas and transparent UWB textile antennas using planar technology for body-centric wireless communications (BCWC). A planar antenna designed using offset-fed and slotted ground plane to extend the operating bandwidth for the industrial, scientific and medical (ISM)band and UWB is proposed. Results show that the antenna can achieve a bandwidth from 2.38 to 14.5 GHz with omni-directional radiation patterns in the E-plane. Agroup of nine planar UWB monopole antennas using different radiator shapes such as triangle, rectangle, square, annual ring, circle, horizontal ellipse, vertical ellipse, pentagon and hexagon for BCWC is studied using computer simulation and measurement. Results show that the monopole antenna having a vertical-elliptical-shape radiator has a relatively better performance than other monopole antennas. Three textile antennas fabricated on fabric materials are studied. The first design is a triple-band textile antenna for wireless-local-area network (WLAN) and worldwide interoperability for microwave access (WiMAX) wireless communication applications. The radiator is composed of two branches and a short stub to generate the resonances at about 2.45, 3.5 and 5.5 GHz, respectively. Simulated and measured results show that the three frequency bands can be set independently. The second design is an UWB antenna consisting of a circular radiator, a tapered feed line and a slotted ground plane. Results show that the antenna can achieve a bandwidth of 3 to 12 GHz. The third design is a compact belt-loop UWB antenna with microstrip-fed. The antenna has a simple elliptical-shaped radiator, a three-step staircase on both sides of the feed line and a slot on the ground plane. It has a very compactsize of 11×40=440 mm2and can still achieve a bandwidth of 3.1 to 12.8 GHz. To emulate the on-body conditions, the two UWB antennas are studied in the bending and crumpling conditions due to the curvature of human body. Results show that both UWB textile antennas have quite stable performances throughout the UWB band. The two UWB textile antennas are re-designed using a transparent conductive film (TCF)as the radiator and ground plane on fabric substrate. Results show that the measured reflection coefficients of transparent antennas agree well with the simulated results. However, the measured radiation patterns have large discrepancies with the simulated results, which are mainly due to the uncertain electric properties of TCF in radio frequency. Results show that the antennas have a better performance, in terms ofbandwidth, peak gain and radiation efficiency ,than those of other transparent antennas studied before, making our proposed antennas suitable for body-centric wireless communications. / published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

This thesis investigates omnidirectional and directional ultra wideband (UWB) antennas for communication and microwave imaging applications. To reduce interference with existing technologies, monopole antennas with efficient band-stop functions are introduced. Single and double slots acting as series resonators are used. Reduction in the antenna gain in the stop-band regions of about 19.5 dB is achieved. Central metal removal and ground plane size effects on the antenna performance are investigated. To eliminate signal distortion caused by such monopole antennas, phase centre behaviour over the entire frequency band of operation is investigated at different principle planes, which have not been done before. This study will also show how these antennas act in different communication scenarios and where the radiation will be coming from at different frequencies. The effect of including different slots with different shapes on the performance of phase centre of these antennas is also investigated. Different methods to minimize the antenna phase centre movement are studied. Novel microstrip antennas with UWB impedance and radiation pattern bandwidth and low cross polarization components are introduced to work over the frequency band from 3 to 20 GHz. The antennas introduced are double-layer structures in which the radiator is sandwiched between two identical partial ground planes or a partial ground plane is sandwiched between two radiators. Results show a significant reduction in the cross polarization components at all frequencies. A novel high gain UWB Vee dipole antenna with a UWB coaxial balun feed is introduced to cover the existing and future UWB communication applications. Different type of loadings such as a reflecting ground below the antenna, a dielectric sleeve over the UWB balun and conical dielectrics between the Vee plates are also used and studied that show enhanced gains and lower sidelobes. A miniaturized-type UWB Vee dipole antenna is also investigated for microwave imaging applications. The antenna has a small radiation aperture which makes it a good candidate for array type applications. Full wave analysis of studied antennas are done using Ansoft HFSS, finite-element-methods based software. Experimental investigations are done to confirm the accuracy of simulated results.

This thesis investigates omnidirectional and directional ultra wideband (UWB) antennas for communication and microwave imaging applications. To reduce interference with existing technologies, monopole antennas with efficient band-stop functions are introduced. Single and double slots acting as series resonators are used. Reduction in the antenna gain in the stop-band regions of about 19.5 dB is achieved. Central metal removal and ground plane size effects on the antenna performance are investigated. To eliminate signal distortion caused by such monopole antennas, phase centre behaviour over the entire frequency band of operation is investigated at different principle planes, which have not been done before. This study will also show how these antennas act in different communication scenarios and where the radiation will be coming from at different frequencies. The effect of including different slots with different shapes on the performance of phase centre of these antennas is also investigated. Different methods to minimize the antenna phase centre movement are studied. Novel microstrip antennas with UWB impedance and radiation pattern bandwidth and low cross polarization components are introduced to work over the frequency band from 3 to 20 GHz. The antennas introduced are double-layer structures in which the radiator is sandwiched between two identical partial ground planes or a partial ground plane is sandwiched between two radiators. Results show a significant reduction in the cross polarization components at all frequencies. A novel high gain UWB Vee dipole antenna with a UWB coaxial balun feed is introduced to cover the existing and future UWB communication applications. Different type of loadings such as a reflecting ground below the antenna, a dielectric sleeve over the UWB balun and conical dielectrics between the Vee plates are also used and studied that show enhanced gains and lower sidelobes. A miniaturized-type UWB Vee dipole antenna is also investigated for microwave imaging applications. The antenna has a small radiation aperture which makes it a good candidate for array type applications. Full wave analysis of studied antennas are done using Ansoft HFSS, finite-element-methods based software. Experimental investigations are done to confirm the accuracy of simulated results.

Thesis (Ph.D.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2008. / Committee Chair: Manos M. Tentzeris; Committee Co-Chair: John Papapolymerou; Committee Member: Andrew F. Peterson; Committee Member: Chang-Ho Lee; Committee Member: John D. Cressler; Committee Member: Joy Laskar.

The continual increase of wireless technologies in the world has motivated the use of phased arrays to mitigate radio frequency interference (RFI). There are many methods of performing beamforming for RFI rejection, but they are traditionally physically large and complicated solutions. Phased arrays need to be shrunk and made cheaper for them to see widespread use. This work presents several compact phased array receivers for different applications. The first part of this thesis presents a software GPS processor for a digital beamforming GPS receiver. The receiver is small enough to be flown on drones and enables GPS signals to be processed and a user’s position to be determined. Using digital beamforming, it can operate even under poor conditions such as intentional jamming, RFI, and large multipath effects. Next, this work builds a frontend RF chain for a true time delay phased array receiver. The receiver uses analog true delay delay chips to mitigate radio frequency interference in sensitive instruments. True time delay allows for analog beamforming over a wide bandwidth, but compact true time delay solutions are new and untested. The receiver allows these solutions to be properly vetted in a full system. The chain uses novel compact wideband antennas for L-band frequencies and traditional low cost amplifiers and filters. The last section of this thesis updates the open-source CASPER project to fully support RF system-on-chips. CASPER is an open-source framework for radio astronomy instruments. It speeds up the design and implementation of radio astronomy instruments on compact platforms and makes them easier to interact with. This work expands the framework to use the transmit abilities of advanced RF system-on-chip platforms. With this expansion, full duplex systems such as communications and radar can now also use CASPER. A full loopback beamforming test built on CASPER demonstrates both transmit and receive beamforming.

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