Dissertations / Theses on the topic 'Reconfigurable and scanning antenna arrays'

This dissertation proposes novel solutions for important drawbacks of antenna arrays. One of the main contributions of the presented work is size reduction and nulling performance improvement of traditionally large anti-jam global positioning system (GPS) arrays using miniature antennas and electrically small resonators emulating an engineered metamaterial. Specifically, a miniaturized coupled double loop (CDL) dual band antenna is first introduced as a small antenna element of the compact GPS array. The loops that are capacitively coupled using lumped element capacitor, and employ metallic pins around their perimeter to improve the radiation efficiency by achieving a volumetric current distribution. This design is employed for the implementation of a compact 2x2 GPS array by reducing the inter-element spacing between the adjacent elements. However, having the antenna elements in close proximity of each other yields to a high mutual coupling and potentially degrades the nulling performance. The mutual coupling is performed by observing the magnetic field distribution within the array. It is noticed that the mutual coupling can be reduced by using metamaterial resonators. The right hand circular polarization (RHCP) radiation nature of the array complicates the mutual coupling suppression as compared to linear arrays. It is determined that split ring resonator (SRRs) are effective to mitigate the mutual coupling problem if placed strategically around the antenna elements. The study is verified experimentally where the mutual coupling is reduced by more than 10 dB. Lowering the mutual coupling improved the array's nulling capability by increasing the nulls depth by 8 dB as well as enhancing the accuracy of the nulls' locations. The second major contribution of the presented work is to introduce a novel microfluidic based beam-scanning technique for the implementation of low cost mm-wave antenna arrays. Traditionally, beam scanning capability is obtained using mechanical steering of the entire antenna structure or electronic components such as switches or phase shifters. The former is bulky, whereas the latter technique requires integrating substantial and expensive hardware in the array's feed network. For instance, a beam-scanning 1x8 focal plane array (FPA) would employ 7 single pole double through (SPDT) switches in its feed network. If an 8x8 FPA is desired, then 8x7+8 switches are required that results in an efficient design in terms of power loss and cost. In this dissertation, the microfluidic principles are introduced for designing and implementing affordable beam scanning antenna array with high gain radiation. Specifically, a microfluidic-based focal plane array 1x8 (MFPA) is designed and implemented at 30 GHz. The proposed MFPA consists of microfluidic channels connecting reservoirs. Both of the channels and reservoirs are filled with a low loss dielectric solution, and the antenna is formed by using a small volume of liquid metal. The beam scanning capability is obtained by placing the array at the focal point of a microwave lens and moving the antenna among the reservoirs using a micropump. Therefore, the feed network is extremely simplified by avoiding using SPDT switches. In addition, a strategic design methodology for a completely passive resonant based corporate feed network is discussed. The array is characterized numerically and verified experimentally. The simulated and measured performances are in a very good agreement with ±300 FoV and > 21 dB realized gain. However, the array's radiation pattern exhibits high side lobe level (SLL) due to the resonant nature of the introduced corporate feed network. Consequently, new resonant and non-resonant straight based feed networks are introduced to alleviate the high SLL issue. Moreover, they are modeled with appropriate equivalent circuits in order to analyze the array's performance analytically in terms of -10 dB |S11| bandwidth and power loss. The analytical solution is based on the transmission line theory and two ports network analysis. It is verified with the full wave simulations and a very good agreement is observed. Using the straight feed network reduces the SLL to more than 20 dB relative the pattern's peak. This enhancement in the performance is verified experimentally as well by designing, fabricating and testing a 30 GHz MFPA fed using a resonant based straight network. A ±250 FoV is obtained with a SLL < -20 dB and 4% -10 dB |S11| bandwidth.

This dissertation introduces new technologies and techniques for low-cost phased arrays and scanning antennas. Special emphasis is placed on new approaches for low-cost millimeter-wave beam control. Several topics are covered. A novel reconfigurable grating antenna is presented for low-cost millimeter-wave beam steering. The versatility of the approach is proven by adapting the design to dual-beam and circular-polarized operation. In addition, a simple and accurate procedure is developed for analyzing these antennas. Designs are presented for low-cost microwave/millimeter-wave phased-array transceivers with extremely broad bandwidth. The target applications for these systems are mobile satellite communications and ultra-wideband radar. Monolithic PIN diodes are a useful technology, especially suited for building miniaturized control components in microwave and millimeter-wave phased arrays. This dissertation demonstrates a new strategy for extracting bias-dependent small-signal models for monolithic PIN diodes. The space solar-power satellite (SPS) is a visionary plan that involves beaming electrical power from outer space to the earth using a high-power microwave beam. Such a system must have retrodirective control so that the high-power beam always points on target. This dissertation presents a new phased-array architecture for the SPS system that could considerably reduce its overall cost and complexity. In short, this dissertation presents technologies and techniques that reduce the cost of beam steering at microwave and millimeter-wave frequencies. The results of this work should have a far-ranging impact on the future of wireless systems.

2010/2011
The material presented in this thesis is the result of the Ph.D. activity carried on between January 2009 and December 2012 at the Ph.D. school in Information Engineering of the University of Trieste. After a brief introduction on the involved topics, the final objective of this thesis is that of presenting the original results, consisting in the development of power pattern synthesis algorithms for arbitrary antenna arrays including, in particular, arrays for satellite applications. Since the earlier satellite missions of last century, satellite communication systems have received growing attention due to the opportunities they offer and their greater flexibility with respect to alternative solutions adopting other media, such as, for example, fiber optic cables. The enormous spread of satellites, for both military and civilian applications, has been achieved thanks to the experienced technological progress, which has allowed an increase of satellite capacities. The need of constantly increasing the capacity of commercial communications satellites resulted in the continuing evolution of the antenna systems onboard the satellites. The business environment has driven the architecture of satellites' systems towards more efficiency and cost consciousness while at the same time, providing flexible access to a growing diversity of services and customers. Antennas that provide a multiplicity of frequency reuse coverage beams through either spatial or polarization isolation have been developed, resulting in the evolution of satellite antennas from a simple omnidirectional dipole to multiple-beam, dual-polarized configurations with frequency reuse between the beams for increased capacity. These requirements translate into high-gain, high-efficiency antennas with low side-lobe levels and excellent polarization purity. Moreover, since new requirements are often determined after the satellite is operational, antennas adjustable to produce a wide variety of radiation patterns have become popular. These are the so-called multiple-beam antennas, which can adjust their radiation coverage areas according to new demands. Multiple-beam antennas are currently being used for direct-broadcast satellites, personal communication satellites, military communication satellites, and high-speed Internet applications. High-gain multiple-beam antenna systems usually take one of three generic forms: lens, reflector or direct radiating array. Thus, arrays of antennas can be used in multiple-beam systems either to feed other types of antennas, or directly as radiating structures. The material of this thesis is mainly related to the synthesis algorithms for antenna arrays. In particular, many analytical and numerical techniques for the power pattern synthesis of antenna arrays have been carefully studied and analyzed. Some of them are suitable only for linear or rectangular arrays, the others for arrays of more complicated geometries. Furthermore, it is extremely important, for power synthesis techniques in satellite applications, to be able to consider additional constraints. These typically are the phase-only reconfigurability of the radiated beams, the control of the cross-polar patterns, which allows the polarization re-use and/or the control of the cross-polar interference, the dynamic range ratio reduction which comports simpler feeding networks and lower mutual coupling between array elements, and the near-field reduction, which allows to take into account the antennas operating environment. A numerical iterative algorithm has been developed during the Ph.D. school in Information Engineering, suitable for arrays of arbitrary geometry, thus including sparse and conformal arrays, which are often used in satellite applications. The algorithm allows to solve the power pattern synthesis problem, which is an inherently non linear problem. The solution is achieved using the alternating projections algorithm, which is a numerical iterative technique for finding a point of the intersection between two sets. It will be seen that the projections method has previously already been applied to problems of image processing and also in the antenna pattern synthesis. However, the results and the computational burden are strongly related to the projection operators, which in turn, strictly depend on the definition of the adopted distance, thus on the definition of the sets adopted in the formulation of the problem. Thus, the main originality of the developed algorithms consists in an extremely advantageous definition of the sets involved in the solving scheme, which, along with the adopted distance, allow an easy evaluation of the projection operators and thus a simple solving procedure. The thesis is organized as follows. Chapter 1 introduces the satellite antennas, analyzing some solutions adopted in the past. Particular attention is devoted to multiple-beam antennas (MBAs) and in particular to arrays of antennas, which can constitute the feeding system of reflector MBAs, or which can be used as direct radiating antennas themselves. Chapter 2 presents analytical and numerical methods of power pattern synthesis for antenna arrays proposed in the literature. First, the classical analytical methods, suitable for linear arrays of equally spaced elements are presented. Then, numerical iterative methods are analyzed. Attention is devoted to both deterministic and stochastic algorithms. A section is dedicated to the near-field constraint, due to its importance in practical real applications. In fact, taking into account the effect of the antenna operating environment is of fundamental importance: obstacles or mounting platforms, as well as other electronic devices located in proximity of the antenna, may strongly degrade the radiated far-field pattern. Then, Chapter 3 presents the developed algorithm. Precisely, the evolution is described from a synthesis algorithm suitable for arbitrary phase-only reconfigurable arrays to a powerful algorithm for phase-only antenna arrays, including several additional constraints, such as the dynamic range ratio reduction, the cross-polar pattern synthesis and the near-field reduction. Moreover, in its final form, the algorithm also allows to minimize the power radiated in the side-lobe regions of both the co- and cross-polar patterns and the electric energy stored in the near-field region of interest. Numerical results validating the effectiveness of the proposed algorithm are presented in Chapter 4 and the conclusions are summarized in Chapter 5. Finally, the appendix mathematically describes the classical alternating projections method and the genetic algorithms, which have been used as global optimization algorithms for comparison purposes.
Il materiale presentato in questa tesi è il risultato dell'attività svolta durante il dottorato tra gennaio 2009 e dicembre 2012 presso la scuola di dottorato in ingegneria dell'informazione dell'università di Trieste. Dopo una breve introduzione sugli argomenti trattati, l'obiettivo ultimo della tesi è quello di presentare i risultati originali che consistono nello sviluppo di algoritmi di sintesi di potenza per antenne a schiera di geometria arbitraria tra le quali, in particolare, schiere per applicazioni satellitari. Fin dalle prime missioni spaziali del secolo scorso, le comunicazioni satellitari hanno ricevuto attenzione crescente grazie alle opportunità che offrono e alla loro maggior flessibilità rispetto a soluzioni alternative che utilizzano altri sistemi, come ad esempio i cavi in fibra ottica. Grazie agli sviluppi tecnologici avvenuti, che hanno reso possibile un aumento delle capacità dei satelliti, si è sperimentata una vasta diffusione di satelliti per applicazioni militari e civili. La necessità di aumentare costantemente la capacità dei satelliti per comunicazioni commerciali ha comportato una continua evoluzione delle antenne da satellite. L'ambiente commerciale ha spinto l'architettura dei sistemi satellitari verso una miglior consapevolezza di efficienza e costi consentendo, allo stesso tempo, un accesso flessibile a un sempre maggior numero di servizi e di utenti. Sono state sviluppate antenne che consentono una molteplicità di fasci con riutilizzo della frequenza grazie ad isolamento spaziale o di polarizzazione. Questo ha generato un'evoluzione delle antenne da satellite dal semplice dipolo omnidirezionale ad antenne a fascio multiplo, con alto guadagno, alta efficienza, bassi lobi laterali ed elevata purezza di polarizzazione. Inoltre, poichè nuove necessità spesso emergono una volta che il satellite è già operativo, si sono diffuse antenne da satellite configurabili in modo da poter produrre diversi diagrammi di radiazione. Queste sono le così dette antenne riconfigurabili, che possono modificare le regioni coperte in base a nuove necessità. Antenne a fascio multiplo vengono usate correntemente in trasmissioni dirette via satellite, satelliti per comunicazioni personali, satelliti per comunicazioni militari e applicazioni Internet ad alta velocità. I sistemi di antenne a fascio multiplo ad elevato guadagno generalmente sono di uno dei seguenti tre tipi: lenti, riflettori o antenne a schiera. Dunque le antenne a schiera si possono trovare nelle applicazioni satellitari sia come strutture per alimentare altri tipi di antenne, sia come strutture radianti direttamente. Il materiale presentato in questa tesi è principalmente legato agli algoritmi di sintesi per antenne a schiera. In particolare, sono stati attentamente studiati e analizzati diversi metodi, analitici e numerici, per la sintesi di potenza di antenne a schiera. Alcuni di questi sono applicabili solo a schiere lineari o rettangolari, altri a schiere di geometria più complicata. Inoltre, è estremamente importante per gli algoritmi di sintesi di potenza di schiere per applicazioni satellitari essere in grado di considerare vincoli addizionali. Questi tipicamente sono la riconfigurabilità del fascio tramite controllo di sola fase, il controllo del diagramma cross-polare, che permette di ottenere il riutilizzo di polarizzazione e/o di controllare l'interferenza cross-polare, la riduzione della dinamica, che permette l'utilizzo di reti di alimentazione più semplici e un abbassamento del mutuo accoppiamento tra gli elementi della schiera, e la riduzione del campo vicino, che permette di tener conto dell'ambiente in cui opera l'antenna. Durante il dottorato è stato sviluppato un algoritmo numerico iterativo per schiere di geometria arbitraria, perciò comprese le schiere sparse e conformi, spesso impiegate in applicazioni satellitari. L'algoritmo permette di risolvere il problema (intrinsicamente non lineare) di sintesi di potenza. La soluzione è ottenuta mediante l'impiego del metodo delle proiezioni succesive, un metodo numerico iterativo per trovare un punto nell'intersezione tra due insiemi. Tale metodo è stato usato in passato in problemi di elaborazione delle immagini e anche in problemi di sintesi di antenne a schiera. Ciononostante, i risultati e il carico computazionale sono direttamente legati ai proiettori, che a loro volta sono strettamente dipendenti dalla definizione della distanza adottata, dunque degli insiemi coinvolti nel problema. Perciò, la principale originalità degli algoritmi sviluppati consiste in una definizione degli insiemi estremamente vantaggiosa in quanto, assieme alla scelta della distanza, permette di valutare facilmente i proiettori e perciò permette di ottenere una procedura di soluzione semplice. La tesi è organizzata come segue. Il primo capitolo introduce le antenne da satellite analizzando alcune soluzioni utilizzate in passato. Particolare attenzione è rivolta alle antenne a fascio multiplo e in particolare alle antenne a schiera, che possono costituire il sitema di alimentazione di antenne a riflettore multifascio o che possono esse stesse essere usate come elementi radianti. Il secondo capitolo presenta metodi analitici e numerici per la sintesi di potenza per antenne a schiera proposti in letteratura. Dapprima vengono presentati i metodi analitici classici, validi per schiere lineari di elementi equispaziati. Successivamente vengono analizzati i metodi numerici iterativi, sia stocastici, sia deterministici. Una sezione a parte è dedicata al vincolo sul campo vicino, vista la grande importanza che riveste nelle applicazioni pratiche. Infatti è di fondamentale importanza tener conto degli effetti dell'ambiente in cui l'antenna opera in quanto ostacoli o strutture di montaggio, così come altri apparati elettronici in prossimità dell'antenna, possono causare forti interferenze e degradare notevolmente il diagramma di campo lontano. Il capitolo 3 presenta gli algoritmi sviluppati. Precisamente, viene delineata l'evoluzione da un algoritmo di sintesi di potenza per schiere riconfigurabili di geometria arbitraria con controllo si sola fase, a un potente algoritmo di sintesi di sola fase con diversi vincoli addizionali, quali la riduzione della dinamica, la sintesi del fascio cross-polare e la riduzione del campo vicino. Inoltre, nella sua forma finale, l'algoritmo permette di minimizzare la potenza irradiata nelle regioni di lobi laterali di entrambi i diagrammi, co- e cross- polare, e l'energia immagazzinata nella regione di campo vicino presa in considerazione. I risultati numerici che provano l'efficacia del metodo sono presentati nel capitolo 4 e le conclusioni sono riassunte nel capitolo 5. Infine, l'appendice descrive matematicamente il classico metodo delle proiezioni successive e gli algoritmi genetici, che sono stati scelti come termine di paragone tra gli algoritmi di ottimizzazione globale.
XXIV Ciclo
1983

Design of antenna arrays for present day requirements has to take into account both mechanical and electrical aspects. Mechanical aspects demand the antennas to have low profile, non-protruding structures, structures compatible to aerodynamic require­ments and so on. Electrical aspects may introduce several constraints either due to. technical reasons or due to readability conditions in practice. Thus, arrays of modern requirements may not fall into the category of linear or planar arrays. Further, due to the nearby environment, the elements will generate complicated individual patterns. These issues necessitate the analysis and synthesis of antenna arrays which are arbi­trary as far as the orientation, position or the element pattern are concerned. Such arrays which may be called arbitrary arrays are being investigated in this thesis. These investigations have been discussed as different aspects as indicated below: Radiation Characteristics of Arbitrary Arrays Radiation fields of an arbitrarily oriented dipole are obtained. Such fields are plotted for typical cases. Further, methods for transforming the electromagnetic fields are discussed. Having obtained the field due to an arbitrary element, the fields due to an arbitrary array are obtained. Factors controlling the radiation fields, like, the curvature in the array and element pattern are investigated. Radiation patterns of circular and cylindrical arrays are plotted. Synthesis of a Side Lobe Topography Requirements of a narrow beam pattern generated by an antenna array are identified. A problem of synthesizing such a pattern using an arbitrary array is formulated. The envelope of the side lobe region which may be called, the side lobe topography (sit), is included in the computation of the covariance matrix. This problem which has been formulated as a problem of minimizing a quadratic function subjected to a system of linear constraints is solved by the method of Lagrangian multipliers. An iterative procedure is used to satisfy all the requirements of the pattern synthesis. The procedure has been validated by synthesizing linear arrays and is used to synthesize circular and parabolic arrays. Patterns with tapered sit, Taylor-like sit have been synthesized. Asymmetric patterns are also synthesized. Role of sit is brought out. Shaped Beam Synthesis Synthesis of shaped broad beams is discussed. Amplitude constraints are formulated. Phase distribution is linked with the phase centre. Quadratic problems thus formu­lated are solved by the Lagrangian method of undetermined multipliers. An iterative procedure is made use of to synthesize flat topped beams as well as cosecant squared-patterns using linear arrays as well as circular arrays. Reasonable excitation dynamic has been obtained. Optimum phase centres obtained by trial and error are made use of. Effects of the Frequency and Excitation on the Synthesized Patterns In general, synthesized patterns can be sensitive towards any specific parameter either excitation or to frequency or any such parameter. Several methods can be used to observe these issues. In this thesis, these effects are also studied. Using a specific array configuration, to synthesize a specified radiation pattern, frequency is changed by 10% from the design frequency and the pattern is computed. Similarly, excitation phase distribution is rounded to the nearest available phase distribution using a digital phase shifter (say 8 bit) and the resulting pattern is computed. Further, excitation dynamic is also controlled by boosting the amplitudes of the array elements which are less than the permissible (i.e. the maximum excitation/allowed dynamic). Effects of these variations are also recorded. It appears that reasonable patterns can be obtained, in spite of significant variations in these parameters in most of the cases. Reconfigurable Arbitrary Arrays It would be very useful if a single array configuration can be used for different ap- plications. This may be either for the different phases of a single application or for different applications that may be required at different times. Attempts are made to synthesize a variety of patterns from a single array. Such arrays which may be called as reconfigurable arrays can be of much use. Obviously, the excitations are different for different patterns. Both narrow beams, as well as shaped broad beams, with different side lobe topographies have been synthesized using a single array.

Antennas enable wireless communication by transmission and reception of electromagnetic (EM) signals, which carry information is space. Signal reception and hence the quality of service depends significantly on the antenna properties, e.g. radiation pattern, operational frequency, and polarization. Legacy antennas, with their fixed properties, fail to adapt to the changing environment and degrade signal quality. Reconfigurable antennas (Ras) capable of changing their properties dynamically increase the capacity and data rate of wireless systems while offering a compact design. However, these advantages come at the cost of increased complexity compared to legacy antennas. Therefore it is important to design Ras with minimal complexity. To that end, this dissertation focuses on the development of a novel approach, three different Ras operation at three different frequency bands have been designed, fabricated and characterized. First RA works at the 5GHz band (4.9-5.1GHz) and obtains on current beam steering and 3-dB beam width variability. An algorithm to choose the optimum mode of operation has also been developed. The design approach introduced in first RA has been exploited to design the second RA, which achieves beam steering and beam width variability for two polarizations and operates a the 28 GHz band (27.5-28.3 GHz). The third RA operates at the 3GHz band and simultaneously reconfigures impedance and radiation patterns.

To meet the ever increasing demand of high data rate, millimeter-wave (mm-wave) wireless communication has become an area of intense research due to the capability of offering very broad bandwidth. However, the propagation losses increase as a function of operation frequency. Therefore, there is need for antenna systems with high gain and beam-steering capability at elevated frequencies, which comes at the expense of high cost and increased complexity. This dissertation demonstrates the design, micro-fabrication, and characterization of two different antennas and two different antenna arrays. A broadband patch antenna operating within (57-66) GHz band, which works as a building block to create a multifunctional reconfigurable antenna (MRA) that is capable of beam steering in three directions pertaining to θ ∈{-30°, 0°, 30°}; Φ=90°. These standalone antennas were then put in a linear formation to create a 2x8 planar array and a 4x1 multifunctional reconfigurable antenna array (MRAA) to increase the gain further and to offer wider bandwidth. The proposed novel MRA and MRAA possess variable element factors, which potentially can feature as the main building blocks of mm-wave reconfigurable wireless communication systems with reduced cost and complexity.

Adaptive array antennas use has been limited to non-commercial applications due to their high cost and hardware complexity. The implementation cost of adaptive array antennas can be kept to a minimum by using cost effective antennas, reducing the number of elements in the array and implementing efficient beamforming techniques. This thesis presents techniques for the design of adaptive array antennas which will enable their cost effective implementation in wireless communication systems. The techniques are investigated from three perspectives, namely, reconfigurable antenna design, wide scan array design and single-port beamforming technique. A novel single-feed polarisation reconfigurable antenna design is proposed in the first stage of this study. Different polarisation states, namely, linear polarisation (LP), left-hand circular polarisation (LHCP) and right-hand circular polarisation (RHCP), are achieved by perturbing the shape of the main radiating structure of the antenna. The proposed antenna exhibits good axial ratio (< 3 dB at 2.4 GHz) and has high radiation efficiency in both polarisation modes (91.5 % - LHCP and 86.9 % - RHCP). With a compact single feeding structure, the antenna is suitable for implementation in wireless communication devices. The second stage of the study presents the design procedure of wide scan adaptive array antennas with reduced number of elements. Adaptive array antennas with limited number of elements have limited scanning range, reduced angular scanning resolution and high sidelobe levels. To date, design synthesis of adaptive array antennas has been targeted on arrays with a large number of elements. This thesis presents a comprehensive analysis of adaptive array antennas with less than 10 elements. Different array configurations are analysed and various array design parameters such as number of elements, separation between elements and orientation of the elements are analysed in terms of their 3 dB scan range. The proposed array, the 3-faceted array, achieves a scanning range up to ±70°, which is higher than ±56° obtained from the Uniform Linear Array. The faceted arrays are then evaluated in the context of adaptive beamforming properties. It was shown that the 3-faceted array is suitable for adaptive array applications in wireless communication systems as it achieves the highest directivity compared to other faceted structures. The 3-faceted array is then synthesised for low sidelobe level. Phase correction together with amplitude tapering technique is applied to the 3-faceted array. The use of conventional and tuneable windowing techniques on the 3- faceted array is also analysed. The final stage of the study investigates beamforming techniques for the adaptive array antenna. In the first part, beamforming algorithms using different performance criteria, which include maximum signal-to noise-ratio (SINR), minimum (mean-square Error) MSE and power minimisation, are evaluated. In the second part, single-port beamforming techniques are explored. In previous single-port beamforming methods, the spatial information of the signals is not fully recovered and this limits the use of conventional adaptive beamforming algorithms. In this thesis, a novel signal estimation technique using pseudo-inverse function for single-port beamforming is proposed. The proposed polarisation reconfigurable antenna, the 3-faceted array antenna and the single-port beamforming technique achieve the required performance, which suggests the potential of adaptive array antennas to be deployed commercially, especially in wireless communication industry.

Recently, reconfigurable antennas have attracted significant interest due to their high adaptation with changing system requirements and environmental conditions. Reconfigurable antennas have the ability to change their radiation pattern, frequency or polarization independently according to the application requirements. In this thesis, three different reconfigurable antenna structures have been designed
beam-steerable meanderline antenna, dual circularly polarized meanderline antenna and dual-frequency slot-dipole array. Traveling wave meanderline antenna arrays are investigated in detail and a beam-steerable traveling wave meanderline antenna array has been introduced for X-band applications. Beam-steering capability of the antenna array has been achieved by loading the antenna elements with varactor diodes. Theoretical analysis and computer simulations of the proposed antenna have been verified with experimental results. Radiation direction of the 8-element meanderline array can be rotated 10°
by changing the varactor diode&rsquo
s bias voltage from 0V up to 20V. Also, a polarization-agile meanderline antenna array has been designed and simulated. Polarization of the circularly polarized meanderline array can be altered between right hand circularly polarized and left hand circularly polarized by using RF MEMS switches. The third type of reconfigurable antenna investigated in this thesis is a dual frequency slot-dipole array operating at X- and Ka-band. Electrical length of the slot dipoles has been tuned by using RF MEMS switches. Antenna prototypes have been manufactured for &lsquo
on&rsquo
and &lsquo
off&rsquo
states of RF MEMS switches and it has been shown that the operating frequency can be changed between 10 GHz and 15.4 GHz.

De nos jours, les communications sans fil sont devenues un moyen incontournable et universel d'échange d'un large éventail d'informations entre différents systèmes, certains d'entre eux étant en mouvement comme des drones parmi tant d'autres. Dans le contexte de cette thèse nous considérons une liaison entre un projectile et une station de base. La géométrie de la structure ainsi que les contraintes aérodynamiques d'un tir balistique impliquent l'utilisation d'antennes patchs dans la partie conique à l'avant du projectile. Ce type d'antenne est facile à intégrer à une plate-forme en tant que réseau conformé tout en respectant les contraintes d'encombrement. Ces communications doivent être fiables et discrètes dans un environnement perturbé ou hostile. Les diagrammes de rayonnement du réseau d'antennes doivent présenter des caractéristiques spécifiques, notamment dans le cas particulier d'objets volants et possédant une rotation en roulis (rotation autour de son axe) qui impliquent l'utilisation d'un réseau phasé et commuté par rapport à sa position. Une antenne qui présenterait un rayonnement fixe assurerait une liaison avec un interlocuteur, mais rayonnerait également dans d'autres directions sensibles ce qui pourraient interférer avec la communication principale. La solution qui consiste à activer et désactiver des sous-réseaux verticaux afin d'orienter le lobe principal dans la plan orthogonal à la pointe semble être en accord avec les contraintes de la structure tournante. Un réseau conique a été étudié puis 2 prototypes ont été fabriqués, dont un à l'ISL. Les sous-réseaux sont répartis de manière égale autour de la pointe de façon à pouvoir rayonner dans toutes les directions. De plus, chaque sous-réseau est composé de trois éléments ce qui permet d'orienter également le lobe principal dans le plan longitudinal de la pointe (le long de l'axe du projectile) grâce à un dépointage électronique. Un système électronique de formation de faisceaux a été développé dans le but de contrôler 12 éléments rayonnants. Le réseau d'antennes ainsi que le circuit de répartition ont été caractérisés dans un premier temps de manière indépendante afin d'optimiser les lois de phase nécessaires à dépointer le lobe à partir des pondérations mesurées. Au final, le réseau de 12 éléments associé à son système d'alimentation dédié a été mesuré dans les chambres anéchoïques de DGA-MI et de l'ISL et les mesures sont en accord avec les simulations
Nowadays wireless communications have become a useful and universal mean to exchange a wide range of information between different systems, some of them being moving, as UAVs among others. In this context we consider here the link between a projectile and a base station. The shape of the structure and the aerodynamic constraints involve the use of patch antennas in the conical front part. This class of antenna is easy to be integrated into the platform as a conformal array, while respecting space constraint. Communications have to be reliable and discrete in disturbed or hostile environment. Antennas array radiation patterns must have some specific characteristics, in particular in the case of flying objects with spin which involves the use of a switched phased array considering its roll position. A fixed-radiation pattern antenna may presents a relevant level or gain toward the interlocutor, but also toward sensitive directions, in which may be located others systems, interfering with the current communication. The solution to switch on and off vertical sub-arrays to steer the beam in the azimuthal plane seem convenient ant fitting the requirements of rotating platform. A conical phased array was studied and two prototypes were manufactured, one at ISL. Sub-arrays are distributed around the conical shape in order to be able to radiate in each direction. Moreover, each sub-array are composed of three radiating elements allowing to steer the main antenna beam in many direction (along the projectile fuze axes). A beam forming network was developed to control the 12 radiating elements conical array. The antenna array and the feeding network were characterized independently in order to optimized the phase of each radiating element. Finally, measurements were done on the whole system in the DGA-MI and ISL anechoic chambers and are in good agreement with simulation results

Les travaux de cette thèse s’intéressent à un nouveau concept d’antenne reconfigurable offrant un bon compromis entre performances, complexité et coût. Ce concept, qualifié d’hybride, vise à combiner les avantages des réseaux d’antennes lacunaires et des antennes à éléments parasites. Cette hybridation est une alternative à la complexité des réseaux d’antennes conventionnels pour répondre aux exigences d’une architecture modulaire, générique et reconfigurable. L’intérêt majeur de ce concept est de proposer une architecture d’antenne permettant de réduire la complexité du circuit de formation des faisceaux (par la réduction du nombre d’éléments rayonnants à alimenter) tout en adressant les problématiques d’adaptation (TOS actif) des éléments excités. Ceci est permis grâce à la présence d’éléments parasites qui permettent de gérer la diffusion des couplages sur l’antenne. Cette thèse décrit le principe du concept hybride et propose une évaluation de ses potentialités. Par la suite, une définition des éléments à mettre en œuvre pour réaliser une preuve de concept est effectuée, en mettant l’accent sur l’importance de la caractérisation expérimentale. Les performances d’un prototype d’antenne hybride reconfigurable sont ensuite présentées afin de valider les développements et conclure sur cette solution innovante
The work of this thesis aims to investigate a new concept of reconfigurable antenna allowing a good trade-off between performances, complexity and cost. This concept is called ‘hybrid’ because it is based on the capabilities of thinned arrays and parasitic element antennas. It is an alternative to classical antenna arrays and their complexity. The proposed concept has a modular architecture, and a good versatility for reconfigurable beams. The main advantage of this hybrid antenna is the simplicity of its beam formation network (BFN) which requires only a few number of excited elements. The antenna uses parasitic elements to manage the effects of couplings between the electromagnetic access. The problematic of active VSWR is also solved at the antenna level, avoiding the use of additional components in the BFN. This work details the principle of the reconfigurable hybrid antenna concept. The potentialities are evaluated. The elements required to realize a proof of concept are then defined, using a dedicated experimental setup. A prototype is manufactured and the performances have been checked to validate this innovative concept

Floating-gate transistors similar to those used in FLASH and EEPROM can be used to build reconfigurable analog arrays. The charge on the floating gate can be modified to pass or block a signal in a cross-bar switch matrix, or it can be finely tuned to eliminate a threshold difference across a chip or set a bias. By using such a compact and versatile reconfigurable analog memory element, the number of analog circuit components included on an integrated circuit that is field-programmable is significantly higher. As a result, large-scale FPAAs can be built with the same impact on analog design that FPGAs have had on digital design. In my research, I investigate the areas floating-gate transistors can be used to impact FPAA design and implementation. An FPAA can be broken up into two basic components, elements of connection and elements of computation. With respect to connection, I show that a floating-gate switch can be used in a cross-bar matrix in place of a transmission gate resulting in less parasitic capacitance and a more linear resistance for the same size transistor. I illuminate the programming issues relating to injecting a floating-gate for use as a switch, including the drain selection circuitry and rogue injection due to gate induced drain leakage. With respect to computation, I explain how a Multiple-Input Translinear Element, or MITE, can be augmented to fit in an FPAA framework. I also discuss two different MITE implementations compatible with CMOS technology, a subthreshold MOS design and a BJT MITE that uses a lateral BJT. Beyond FPAA components, I present two alternative FPAA systems. The first is a general purpose reconfigurable analog system that uses standard analog design components that have been augmented with floating-gates. The second FPAA is built upon MITE circuits, and is focused on supporting direct system synthesis. I conclude with a discussion of a future large-scale MITE FPAA.

La demande toujours croissante de connectivité et de débit de données requiert une rupture dans la conception des futurs réseaux de communication et systèmes radio. Plusieurs applications émergentes en bande millimétrique, notamment les réseaux mobiles de cinquième génération (5G) et les communications satellites, exigent des antennes large bande qui assurent une grande couverture angulaire, tout en étant à la fois compactes, facilement intégrables et à bas coût.Cette thèse propose des systèmes antennaires multifaisceaux large bande et à très grande couverture angulaire, appelés «Continuous Transverse Stub Antenna» (CTS), pour réaliser un bon compromis de l’ensemble de ces objectifs. L’architecture de l’antenne comprend un réseau de fentes longues excitées par un réseau d’alimentation en chandelier, basé sur des guides d’onde à plans parallèles. Cette structure est excitée par un formateur de faisceaux quasi-optique co-intégré. La première partie du manuscrit présent des nouveaux modèles numériques qui facilitent la conception de chaque sous-système de l’antenne et permettent l’analyse des performances globales, soit en termes d’adaptation, soit en termes de diagrammes de rayonnement. Ces outils sont exploités pour la conception d’antenne et pour étudier les limites en balayage. La thèse se poursuit en présentant de nouvelles solutions technologiques et de nouveaux design pour intégrer les antennes CTS dans des modules multicouches planaires et à faible profil. La conception et la caractérisation de deux antennes intégrées en technologie LTCC pour des points d’accès 5G à 60 GHz sont discutées. L’une des deux est à faisceau fixe, l’autre est à balayage électronique, avec une couverture de ±40°, de faibles lobes secondaires et un niveau élevé de recoupement des faisceaux. Enfin, nous proposons l’association de radomes polarisants planaires à faible profil aux antennes CTS, pour réaliser des systèmes rayonnants en polarisation circulaire. Une méthodologie systématique pour la conception de polarisateurs à très large bande est présentée, ainsi qu’un design couvrant entièrement la bande Ka pour des applications satellites
The ever-growing demand for fast and seamless connectivity shows the need of new wireless standards and technologies. Novel broadband, wide-angle scanning antennas achieving an optimal trade-off among size, gain, efficiency and costs are crucial to the development of emerging applications at millimeter waves, such as fifth-generation (5G) mobile networks and satellite communications. In this thesis, multibeam parallel-fed continuous transverse stub (CTS) array antennas are proposed as possible candidates for future mm-wave communications and are developed to tackle these requirements. The antenna architecture comprises an array of long slots, a corporate feed network based on parallel plate waveguides (PPWs) and an integrated quasi-optical beamformer. First, novel numerical models for the analysis of each subsystem and of the overall antenna, are presented, which enable an efficient and modular design of CTS antennas. These tools are exploited to derive design guidelines and assess the scanning performance. Then, novel design and technological solutions for the integration of CTS antennas in flat, low-profile multilayer modules are discussed. The design and characterization of two prototypes in LTCC technology, for 60-GHz mobile access points are presented: a fixed beam array and a switched-beam antenna with a field of view of ±40°, low SLLs and high beam overlap. Finally, planar linear-to-circular polarization converters are proposed to realize circularly polarized CTS antenna systems. A procedure to achieve an ultra-wideband, low-loss polarization conversion is outlined and a design for Ka-band satellite application is presented

L’évolution rapide des communications sans fil et reconfigurables demande des systèmes antennaires avancés qui sont capables de satisfaire des besoins en termes d’agilité des diagrammes, un fort gain et un fonctionnement large bande. Afin de répondre à ces nouveaux besoins, la solution proposée dans cette thèse est basée sur l’ARFFR proposée par le laboratoire XLIM pour obtenir un compromis très intéressant en termes de performances / consommation énergétique / coût. Ces travaux ont notamment été utilisés dans le cadre d’une thèse (2012-2015) pour démontrer la faisabilité sur un premier démonstrateur à base de monopoles à 2.45 GHz en simple polarisation. Dans cette thèse, nous avons visé à introduire ce concept d’ARFFR pour gérer les problématiques des réseaux d'antennes périodiques. Deux axes principaux ont été développés au cours de ces travaux. Le premier axe consiste à montrer l’intérêt de ce concept à gérer la problématique de ROS actif du panneau tout en minimisant le nombre d’accès alimentés au BFN grâce à la présence des charges appliquées aux éléments parasites, sans avoir à rajouter des circulateurs derrière chaque élément rayonnant. La deuxième partie de ces travaux s’intéresse à exploiter les propriétés de ce concept d’ARFFR pour diffuser l’énergie des lobes de réseau en définissant des contraintes sur le niveau de lobes secondaires. Un prototype a été étudié et réalisé permettant de valider expérimentalement les potentialités de ce concept
The fast development of wireless communication led to an increasing demand for new developments on antennas. These developments were backed by an urgent need for more complex architectures due to the need of reconfigurability in terms of frequency, reliability, radiation pattern and power consumption. In order to cover those needs, this work is based on an original reconfigurable antenna with a simplified feed network developed by XLIM laboratory, to offer an attractive tradeoff in terms of performances, complexity and cost. This new architecture is based on previous works from the laboratory (2012-2015) and a first proof of concept working at 2.45 GHz. The work proposed for this PhD is based on the development of this new architecture to manage the problems of periodic antenna arrays. Two main axes were developed during this work. The first axis consists to demonstrate the interest of this concept to manage the active VSWR of each excited element using loads connected to the parasitic elements, avoiding the need for circulators, while reducing the complexity of feed network. The second part of our work is dedicated to illustrating the potentialities of these antennas to reduce the grating lobes, while defining a constraint on the level of sidelobes. A manufactured prototype is presented in order to experimentally validate the potentialities of these antennas

De par les caractéristiques uniques de l'Internet des objets (IoT), telles qu'un volume massif de données, des contraintes de ressources strictes et des niveaux d'activité hétérogènes, les futures infrastructures IoT sans fil doivent intégrer des solutions d'auto-organisation intelligentes pour fonctionner efficacement dans l'environnement IoT dynamique.Dans ce contexte, cette thèse présente le développement de systèmes d'antennes intégrés reconfigurables innovants capables de s'adapter à de tels réseaux IoT sans fil dynamiques et polyvalents.Dans un premier temps, ce manuscrit de thèse traite de la conception d'antennes adaptées à une intégration dans des terminaux IoT lorsque des propriétés de rayonnement spécifiques ou des opérations multi-bandes sont nécessaires. Les structures d'antennes et les techniques d'intégration sont présentées pour les applications IoT à bande unique et multibande. Dans ce cadre, une méthodologie de conception basée sur une antenne à structure unique multi-accès et une antenne à polarisation circulaire omnidirectionnelle miniaturisée pour les applications IoT sont décrites. Ensuite, une approche basée sur les réseaux de neurones pour estimer les performances de petites antennes compte tenu des contraintes pratiques est présentée. Comme preuve de concept, le cas des antennes imprimées intégrées dans des terminaux compacts est étudié.Dans une seconde partie, la thèse porte sur le développement d'antennes reconfigurables compactes et peu gourmandes en énergie. Afin de permettre de nouvelles applications, telles que les communications portables, et d'offrir des performances supérieures dans une variété d'environnements d'intégration, une antenne flexible et reconfigurable est présentée. Pour garantir un fonctionnement fiable, les antennes flexibles doivent en effet conserver des caractéristiques radioélectriques ou de rayonnement approprié et ceci, malgré la modification de leur structure créée par la flexibilité. Le mécanisme de reconfiguration de l'antenne proposée pour les contraintes évoquées permet le décalage de sa résonance, la rendant ainsi capable de maintenir une adaptation d'impédance acceptable sur toute la bande de fonctionnement même lorsqu’elle est repliée.Une antenne compacte reconfigurable à gain et rapport avant/arrière élevés pour le filtrage spatial dans les réseaux IoT est ensuite proposée. Le mécanisme de reconfiguration est basé sur l'utilisation d'un commutateur SP4T à faible pertes d’insertion et à faible résistance, qui peut être contrôlé numériquement par un microcontrôleur, comme l'exigent les applications IoT. Une antenne à réseau parasite, avec faisceau orientable électroniquement (ESPAR, pour electronically steerable parasitic array radiator), à base d’éléments rayonnants de type fentes adaptée aux applications IoT est ensuite présentée. Le travail décrit en profondeur la procédure de conception de l'antenne, en abordant également la mise en œuvre pratique du mécanisme de reconfiguration, et se concentrant sur la réalisation du prototype et sa caractérisation expérimentale.Enfin, une méthodologie de synthèse de réseaux d'antennes parasites est proposée. Cette méthode est basée sur l'utilisation d'un algorithme de type PSO (Particle Swarm Optimizer), qui optimise de manière itérative les impédances complexes des charges connectées sur les éléments parasites jusqu'à ce que le comportement en rayonnement souhaité soit obtenu. Afin d'évaluer la capacité de la méthode à atteindre les objectifs souhaités, la méthodologie est utilisée pour optimiser la directivité, le rapport avant/arrière et le gain d’antennes à réseau parasite compactes destinées aux appareils IoT. Les valeurs des impédances de charge identifiées avec cette approche sont intégrées dans les structures d'antenne pour réaliser le réseau d'antennes parasites. La reconfiguration peut alors être simplement obtenue en réalisant une permutation circulaire des valeurs de la charge sur les éléments parasites
Because of the unique characteristics of the Internet of things (IoT), such as massive volume of data, stringent resource constraints, and heterogeneous activity levels, future wireless IoT infrastructures must integrate smart self-organizing solutions to efficiently operate in the dynamic IoT environment.Within this context, this thesis presents the development of innovative integrated reconfigurable antenna systems capable of adapting to such dynamic and multi-purposed wireless IoT networks.As a first step, the thesis covers the design of antennas suitable for integration in IoT terminals when specific radiation properties or multi-band operations are needed. Both antenna structures and integration techniques are presented for single and multi-band IoT applications. Next, a design methodology based on a multi-access single structure antenna and a miniaturized omnidirectional circularly polarized antenna for IoT applications are presented. Successively, an approach based on Neural Networks (NN) to estimate the performance of small antennas given practical constraints is presented. As proof of concept, the case of printed antennas integrated into compact terminals is considered.In the second part, the thesis focuses on the development of compact and low-power-consuming reconfigurable antennas. In order to enable new applications, such as wearable communications, and to deliver higher performance in a variety of integration environments, a flexible, reconfigurable antenna is presented. To guarantee reliable operation, flexible antennas must maintain proper electrical or radiation characteristics despite the variation of their structure given by the flexibility. Consequently, the reconfiguration mechanism of the proposed antenna allows the shift of the antenna resonance, making the antenna capable of maintaining an acceptable impedance matching over the operating band even when the antenna is folded.A compact high gain and front-to-back ratio pattern reconfigurable antenna for spatial filtering in IoT networks is then proposed. The reconfiguration mechanism is based on the use of a low-insertion, low-on resistance SP4T switch, which can be numerically controlled by a microcontroller, as required by IoT applications. Successively, a slot-based electronically steerable parasitic array radiator (ESPAR) antenna suitable for IoT applications is presented. The work describes in-depth the design procedure of the antenna, addressing the practical implementation of the reconfiguration mechanism, and focusing on the realization of the prototype and its experimental evaluation.Finally, a methodology for synthesizing parasitic antenna arrays is proposed. The method is based on the use of a Particle Swarm Optimizer (PSO), which iteratively optimizes the parasitic element loads until the desired pattern behavior is obtained. In order to assess the method's ability to address the desired goals, the methodology is used to optimize the directivity, the front-to-back ratio, and the gain of compact parasitic array antennas for IoT devices. The impedance loads values identified with this approach are integrated into the antenna structures to realize the parasitic antenna array. Reconfiguration can then simply be obtained by rotating the load's values over the parasitic elements

碩士
國立彰化師範大學
電機工程學系
104
A design for beam steering antenna arrays is described. The radiating element of the array is mainly composed of dual coplanar slotted-patch antennas, a metallic reflector, and several PIN diodes embedded in the slots. By controlling the states of the diodes, the operation of the slotted-patch antennas can be switched among three modes. These operation modes can generate three radiation beams respectively directed to ɸ = 0°, 40°, and −40° in the H-plane. Based on the pattern reconfigurable antenna element, a three-sector triangular array operated at 2.2 GHz is developed. The measured results demonstrate that the sector array can provide nine radiation beams which are steerable over a full 360° in the azimuthal plane; in addition, each switched beam has a half-power beamwidth of about 60° and a cross polarization level of lower than -20 dB. In the other hand, a linear array operated at 2.2 GHz is developed. The measured results demonstrate that the gains of three modes have 10.7 dB almost. Compared with simulated results, it has less than 3.5 dB. The main reason of losses is ohmic and transmission. A design for arrays with beam-steering capability in the azimuthal plane is described. The array is a four-sector antenna configuration,and each sector element can generate unidirectional radiation with circular polarization (CP). A reconfigurable 1 × 4 power divider with broadband operation is designed and used to excite the sector elements. By controlling PIN diodes, the divider can offer 11 states for the four outputs, and each state is corresponding to one CP radiation pattern of the array. Prototypes for the sector array and the tunable divider are, respectively, constructed, and the experimental results of the integrated structure demonstrate that, in addition to the beam-steering capability, the array can also generate bidirectional and omnidirectional radiation patterns between 1.9 and 2.3 GHz. Moreover, these steerable beams and radiation patterns have a cross polarization of less than −18 dB for all azimuthal angles.

This thesis examines a series of near-field antenna arrays used to perform subwavelength focusing and subwavelength imaging outside the extreme near field. For this purpose, slot and dipole arrays have been designed to produce a subwavelength focal spot at a distance of a quarter wavelength from the array. The dipole arrays are then used as scanning probes to produce images with subwavelength resolution based on perturbations in the scattered field. Unlike negative-refractive-index metamaterial superlenses, the imaging resolution is not affected by losses in the array. Furthermore, the arrays are simple to fabricate and are frequency scalable up to Terahertz frequencies and beyond. A near-field analogue to classic antenna-array theory called ``shifted beam theory'' is presented as a design tool. Based on the linear independence of element field patterns in the near field, this theory is very intuitive and provides a simplified way to calculate the element current weights necessary to generate a given target near-field pattern. Two-dimensional near-field subwavelength focusing is demonstrated using a slotted transmission-screen, or ``meta-screen'', under plane-wave incidence. At a distance of a quarter wavelength, the transverse electric field was measured in experiment to have a full-width half-maximum beamwidth of 0.40 by 0.27 wavelengths. This is compared to a single slot transmission-screen which had a beamwidth of 0.60 by 0.58 wavelengths. Broadside and end-fire dipole arrays are used to perform subwavelength imaging in one and two dimensions, respectively. The experimental minimum resolvable separation between two objects at a quarter-wavelength distance was 0.26 wavelengths using the end-fire array probe, as compared to 0.43 wavelengths for a single monopole probe. For an experiment using eight objects scattered over a one-square-wavelength area, however, the array probe imaging resolution remained around 0.25 wavelengths while the baseline monopole probe was no longer able to resolve any of the objects. Experiments were also conducted using objects buried behind a dielectric barrier as well as objects immersed within a dielectric. These results were consistent with the resolution improvements observed in the free-space resolution experiments.

Conventional microstrip antenna feeding techniques using microstrip transmission lines or coaxial probes limit the bandwidth to a few percent due to feed radiation and reactive mismatch. Proximity-coupled feeds can be used as an alternative to direct contact feeds on thick substrates by coupling to an embedded microstrip line or by stacking several patches. Proximity coupled element bandwidths of up to 25% have been achieved with single patch elements, but no models presented thus far can predict the effects of inter-element coupling upon resonant frequency and bandwidth. This paper presents an infinite array analysis which is applied to three types of proximity coupled rectangular microstrip elements. The spectral dyadic Green's function for a two layer grounded dielectric slab is used so that all surface wave and mutual coupling effects are included. A method of moments with three types of expansion modes is used to efficiently solve for the unknown current distribution, and a model for microstrip traveling wave feed lines in an infinite array is described. Theoretical results are presented for scanning input impedance as a function of substrate parameters, array spacing, and element geometry. Experimental data from a waveguide simulator and an 11 x 11 array are shown to validate the analysis.

碩士
國立交通大學
電信研究所
85
This project is to design, fabrication and measure the Ku-band phase-shifterless beam-scanning active antenna arrays. The beam scanning in linear arrays of antenna-coupled oscillators can operate at desired frequency range with in-phase and stable, then the end elements be slightly detuning frequency to provide continuously phase variation between the elements without phase shifter. Mutual coupling technique is utilized to enable them to synchronize to a common frequency through the phenomenon of injectionThis project is based on the circuit designed by Dr. York*s group of UCSB and Prof. Itoh*s group. In this phase- shifterless beam-scanning antennas arrays, it was shown that a constant phase progression can be established by slightly detuning the peripheral arrays elements, while maintaining mutual synchronization.An experiment for the beam-scanning antenna arrays has been carried out. The oscillation frequency is measured at about 16.7 GHz. It has continuously scan the radiation pattern from . An effective radiation power (ERP) of 85mW、349mW、1789mW is obtained for single-unit, two-unit and four-unit active antenna array.

碩士
國立交通大學
電信工程研究所
105
This thesis studies the reconfigurable hybrid beamforming architecture with dual-polarized phased antenna arrays for millimeter wave (mmWave) communication systems. Traditionally, to implement a MIMO antenna array system, every single antenna requires a RF chain which is a very expensive and high power consumption approach to achieve large-scale multi-antenna array system. In contrast, the hybrid beamforming architecture is a rather cost-effective option since less RF chains are needed. Besides, it not only compensates high path loss in mmWave, but also exploits the degree of freedom in signal processing. Furthermore, we use dual-polarized patch antenna to reduce the effect from the dead zone of single-polarized patch antenna and from the high spatial correlation issue in mmWave communication systems. For the traditional fixed hybrid beamforming system, the connecting of RF chains and antenna arrays is fixed. When the channel conditions or the positions of users change, the system may not achieve the best quality of communication. Based on the traditional architecture, this thesis proposes a reconfigurable hybrid beamforming architecture. Combine the analog multiplexers between RF chains and antenna arrays, let it can dynamically adjust the connecting of RF chains and antenna arrays and conduct space-time code or spatial multiplexing and design their corresponding baseband precoder. Finally, design a training flow to let the system can choose the best operating mode. By the simulation results, the system will adjust to the best operating modes according to the training flow for different channel conditions and the capacity will significantly increase. Comparing with the fixed architecture, the reconfigurable one is more flexible and has another degree of freedom to increase the capacity. For the next generation mobile communication, it is one of the potential techniques.

Indiana University-Purdue University Indianapolis (IUPUI)
This thesis proposes a reconfigurable phased array of antennas for wireless power transfer. The array finds use in many applications, from drone destruction (for defense) to wireless charging of robots and mobile devices. It utilizes a novel feeding architecture to greatly reduce the number of high cost elements (such as amplifiers and phase shifters) as well as the quantity of unused resources in the system. Upon the instruction of the CPU, the array can separate into any number of subarrays, each of which transmits power to a single receiver, steering its beam as the receiver changes location. Currently dormant elements in the array can be used to provide position information about the receivers, either via Radar, or by listening for beacons pulses from the receiver. All of this is made possible, with only 4 amplifiers and 3 phase shifters, by the proposed 4-Bus Method. The source signal is divided into four buses, which are respectively phase shifted by 270 degrees, 180 degrees, 90 degrees, and 0 degrees (no shifter required) and then amplified. The CPU calculates, based on the number and positions of the receivers / targets, what the amplitude and phase excitation must be at each element. Any phase and amplitude which could be required can be achieved by simply adding together appropriate quantities of the correct two buses. In order to achieve this, the key piece is the variable power divider. These differ from Wilkinson dividers in that the dividing ratio can be changed via an applied DC voltage. Therefore, at each junction, by properly diverting the power levels on each phase bus to their proper location, complete delocalization of both amplifiers and phase shifters can be achieved. A method has also been developed which helps overcome the limitations of each variable power divider. That is, in certain instances, it may be desirable to pass all the power to a single output port or the other, which is not a possibility inherently possible with the device. With the use of a unique combination of RF switches, the nodes achieve much enhanced flexibility. Finally, an intensive study is carried out, in an attempt to yield greater understanding, as well as quick, useful approximations, of the behaviors of both rectangular and hexagonal arrays of various sizes and beam steering angles for wireless power.

In modern wireless communication and radar systems, filters play an important role in getting a high-quality signal while rejecting spurious and neighboring unwanted signals. The filters with reconfigurable features, such as tunable bandwidths or switchable dual bands, also play a key part both in realizing the compact size of the system and in supporting multi-communication services. The Chapters II-IV of this dissertation show the studies of the filters for microwave communication. Bandpass filters realized in ring resonators with stepped impedance stubs are introduced. The effective locations of resonant frequencies and transmission zeros are analyzed, and harmonic suppression by interdigital-coupled feed lines is discussed. To vary mid-upper and mid-lower passband bandwidths separately, the characteristic impedances of the open-circuited stubs are changed. Simultaneous change of each width of the open-circuited stub results in variable passband bandwidths. Asymmetric stepped-impedance resonators are also used to develop independently controllable dual-band (2.4 and 5.2 GHz) bandpass filters. By extending feed lines, a transmission zero is created, which results in the suppression of the second resonance of 2.4-GHz resonators. To determine the precise transmission zeros, an external quality factor at feeders is fixed while extracting coupling coefficients between the resonators. Two kinds of feed lines, such as hook-type and spiral-type, are developed, and PIN diodes are controlled to achieve four states of switchable dual-band filters. Beam-scanning features of the antennas are very important in the radar systems. Phase shifters using piezoelectric transducers and dielectric leaky-wave antennas using metal strips are studied in the Chapters V-VII of this dissertation. Meandered microstrip lines are used to reduce the size of the phase shifters working up to 10 GHz, and reflection-type phase shifters using piezoelectric transducers are developed. A dielectric film with metal strips fed by an image line with a high dielectric constant is developed to obtain wide and symmetrical beam-steering angle. In short, many techniques are presented for realizing reconfigurable filters and large beam-scan features in this dissertation. The result of this work should have many applications in various wireless communication and radar systems.

Yes
The paper presents a technique to enhance the isolation between adjacent radiating elements which is common in densely packed antenna arrays. Such antennas provide frequency beam-scanning capability needed in Multiple-Input Multiple-Output (MIMO) systems and Synthetic Aperture Radars (SARs). The method proposed here uses a metamaterial decoupling slab (MTMDS), which is located between radiating elements, to suppress mutual-coupling between the elements that would otherwise degrade the antenna efficiency and performance in both the transmit and receive mode. The proposed MTM-DS consists of mirror imaged Eshaped slits engraved on a microstrip patch with inductive stub. Measured results confirm over 9–11 GHz with no MTM-DS the average isolation (S12) is -27 dB; however, with MTM-DS the average isolation improves to -38 dB. With this technique the separation between the radiating element can be reduced to 0.66λo, where λ0 is free space wavelength at 10 GHz. In addition, with this technique there is 15% improvement in operating bandwidth. At frequencies of high impedance match of 9.95 GHz and 10.63 GHz the gain is 4.52 dBi and 5.40 dBi, respectively. Furthermore, the technique eliminates poor front-to-back ratio encountered in other decoupling methods. MTM-DS is also relatively simple to implement. Assuming adequate space is available between adjacent radiators the MTM-DS can be fixed retrospectively on existing antenna arrays, which makes the proposed method versatile.
Partially supported by innovation programme under grant agreement H2020-MSCA-ITN-2016 SECRET- 722424 and the financial support from the UK Engineering and Physical Sciences Research Council (EPSRC) under grant EP/E022936/1.