Academic literature on the topic 'Reconfigurable and scanning antenna arrays'

This paper presents a design of a wide-angle scanning planar array based on a reconfigurable antenna with four radiation patterns for 5G applications. The pattern-reconfigurable antennas (PRAs), capable of switching into four radiation patterns with the help of PIN diodes, constitute the basic elements of the planar array. By exciting each port individually and combining the scans of the PRAs operating at four symmetrical modes in four quadrant subspaces, the main beam of the proposed scanning planar array can scan subspaces I, II, III, and IV by directing the main lobe from -65° to 65° with side lobes less than -7 dB, while supporting a 3 dB scanning coverage of up to 83.5° for each quadrant in the elevation plane. Due to its compactness, simpler biasing network, and more significant beam-scanning coverage, the scanning array by using four-mode PRAs has better performance, via simulation and measurement result agreement.

In this work, a flexible and reconfigurable feeding network design for a nonuniform aperture on circular concentric ring arrays is proposed and analyzed. The network subsystem delivers coherent in-phase outputs with a Gaussian-like amplitude distribution, in a modular and basic topology based on sets of alternated power combiners and dividers. A complete antenna system in a monobeam configuration with a coherent network based on grouped inputs (blocks) per ring for an aperiodic concentric ring array with beam scanning and beam shaping properties is synthesized and analyzed. Additionally, a comparative analysis based on nonuniform and uniform concentric ring arrays fed by the proposed coherent network configuration is conducted and assessed. The optimization of the aperiodic layout on the antenna aperture (radii and interelement antenna spacings) is done by the differential evolution algorithm. Numeric experimentation demonstrates the performance advantages and capabilities of the proposed coherent network configuration with a nonuniform aperture over its uniform counterpart, with an improvement in average equal to −8.7 dB of side lobe level and 3.9 dB of directivity. Furthermore, the numeric examples show a complexity reduction on the coherent feeding network configuration based on the number of control signal inputs compared with a conventional phased antenna array; in the proposed configuration, the main beam is steered and shaped with N-1 control feeding ports per ring in this antenna system.

In this paper, on the basis of multifunctional reconfigurable pixel antenna (RPA) elements, a novel linear sparse array with an attractive compound reconfigurability is presented. It has the potential advantages of its beam scanning with low gain fluctuation, low sidelobe in two orthogonal planes, and polarization reconfigurable performance. Specifically, an RPA with simultaneous polarization and pattern reconstruction capabilities, consisting of the driven patch and the parasitic pixels on the same layer of dielectric substrate, is firstly designed, which can work in several operation modes corresponding to steerable beam directions θ=0°;θxoz=25°, 45°;θyoz=15° with two circular polarizations in X-band. Cross-slot coupling feed is used to improve polarization reconstruction capability and reduce the complexity of hybrid reconstruction topology optimization. Then, those RPAs are integrated into the 1×8 linear sparse array to realize the reconfiguration of two circular polarizations and beam steering in xoz- and yoz-plane. Simulation results show that the gain fluctuation and sidelobe level of the array during beam scanning have significant advantages over the previous phased array, and the generation of antenna grating lobes is avoided. Moreover, both RPA element and RPA array prototypes have been fabricated and measured to testify the efficiency. The measured results agree well with the simulated ones, which indicates the application potential in the field of modern wireless communication system of the proposed linear sparse array.

A dual-polarized continuous transverse stub (CTS) K-band antenna with reconfigurable four beams and low profile is proposed based on substrate-integrated-waveguide (SIW) design. It consists of a line source generator (LSG) on the bottom surface, a spherical-wave to plane-wave transforming part on the middle layer, and CTS radiators on the top surface. Particularly, the LSG has four SIW-based H-plane horns, and a chip is integrated to switch among the two pairs of horns, so as to transfer the quasi-TEM waves on the bottom surface by a ±10° deflection angle to the middle layer for the CTS radiators on the top surface, resulting in four reconfigurable scanning beams with 10° for two polarizations. The measurements show that it realizes four reconfigurable beams with a 25.8 dBi gain at 24 GHz, verifying the design. The proposed antenna takes into account the advantages of reconfigurable multi-beam, dual polarization, low side lobes, low profile, and high gain, which can be applied to K-band sensing, especially for wind profile radars.

A novel thinned array with symmetric distribution along the array center is proposed in this paper. The proposed symmetric thinned array is based on the theory of unequally spaced array and the amplitude of each element in the array can be changed by introducing the weighted function. The pattern of the proposed array can be properly adjusted by changing the weighted function and the amplitude of the weighted factor, which obviously releases new degrees of freedom in array design. It has advantages such as low side lobe level (SLL) in the visible region, no grating lobes, and low nearby side lobe level (NSL), which has good potential for wide-angle scanning. Both simulation and experiment have been done; the experiment results show that, by applying this novel symmetric thinned array with pattern reconfigurable quasi-Yagi antenna, the scanning range of the array is −70°~70° inH-plane with SLL almost −10 dB below the maximum of the main beam. The 3 dB beam-width coverage is −86°~86°, which means that the proposed array can realize the entire upper-space beam coverage and restrain the SLL at the same time.

A reconfigurable electromagnetic surface has been studied to realize the adjustable orbital angular momentum (OAM) beams for real-time wireless communication and dynamic target detection in the future. OAM mode switching realized by many previous designs suffers from low gains without OAM beam scanning. In this article, a 1-bit reconfigurable reflectarray antenna is designed, fabricated, and tested for the real-time control of OAM mode switching and large-angle vortex beam scanning in three-dimensional space. The proposed reflectarray surface is composed of 1-bit electronically reconfigurable cells, and the size is 24 λ × 24 λ with 2304 units. The reconfigurable element is designed by using a radiation patch loading a PIN diode with effective control of two states, “ON” and “OFF”, for the demand of 180° phase difference. The reflectarray surface can be assigned to a code sequence of 0 or 1 by the Field-Programmable Gate Array (FPGA) in real time. Henceforth, the coding surface can dynamically control the generation of high-gain OAM beams, where only the optimized phase distributions on the surface need to be changed according to demand. To verify the concept, a large-scale reflectarray surface is fabricated and measured with an oblique feed at 15°. Different OAM-carrying phase distributions for different OAM beam states are calculated and tested. The test results show that the OAM mode switching between l = 1 and l = 2 is realized, and other variable modes such as l = 3 or l = 5 can also be achieved by modifying the phase encoding sequence. Furthermore, the direction of the vortex beams can be accurately controlled with gains over 20 dBi, and the large-angle vortex beam scanning is verified. Therefore, all results demonstrate that the proposed 1-bit reconfigurable reflectarray is efficient for the regulation and control of OAM-carrying beams for the demand of real-time dynamic wireless communications in the future.

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.

The objective of this chapter is to show the applications of innovative reconfigurable antenna methodologies for the 4G devices. Microwave antenna technology can be very useful for the 4G devices, because these products will require high bandwidth and high velocity channel with respect to conventional antennas. This chapter presents a complete picture of possible applications of advanced microwave technologies for 4G devices and systems, it includes methodologies, such as phased and fully adaptive arrays, innovative multiple-Input and multiple-output (MIMO) antennas based on compact rotmans lenses or butler matrix, and the development of innovate reconfigurable antenna based on reconfigurable parasitic structures. The chapter ends with some conclusions and considerations related to ideas for future works.

This chapter introduces design and implementation of high-gain broadband antennas for 60-GHz short-range communications. It presents different antenna configurations and architectures that can be good candidates for the 60-GHz industrial, scientific and medical (ISM) band. Printed dipole array (PDA) antennas and especially the Printed log-periodic dipole array (PLPDA) antennas will be discussed in this chapter. Loading these kind of antennas with low-cost spherical or hemispherical dielectric lenses will also be presented and demonstrated to increase the gain of the antenna. Another type of antennas called electromagnetically coupled (EMC) elliptical patch antenna arrays will be investigated. Antipodal Vivaldi antenna and corrugated antipodal Vivaldi antenna are also introduced as good candidates for 60-GHz short-range communication applications.

This article is devoted to showing the applications of innovative reconfigurable antenna systems suitable for the next generation 4G/5G devices. Microwave antenna technology can be very useful for next generation devices based on 4G/5G standards. Next generation tablets and smartphones based on 4G/5G standards will require high bandwidth and high velocity channels with respect to conventional devices. This work tries to present a complete overview of possible applications of advanced antenna technologies for 4G/5G devices and systems. Methodologies, such as phased and fully adaptive arrays, multiple-input and multiple-output (MIMO) antennas based on compact Rotman lenses or butler matrices, development of innovate reconfigurable antennas based on reconfigurable parasitic structures or new materials such as graphene, and unconventional modulation techniques have been investigated in this work. The work ends with some conclusions and considerations related to ideas for future works.