This thesis investigates optical feed methods for phased array antennas. The technical and practical limitations are analyzed and an optimum design is determined. This optimum optical feed is a two-beam interferometric approach which uses acoustooptic phase control. The theory is derived; a computer model is developed; and the limitations are determined. Design modifications are suggested which reduce limitations and greatly extend the range of applications. / Master of Science

Precise radiation pattern control for an array antenna requires precise control of array element excitations. One application is that of low side lobe patterns. Classical synthesis methods for the desired pattern may not be realized in practice due to coupling effects. Coupling occurs in two forms: the mutual coupling between array elements and the coupling introduced by the feed networks. Ideally one could account for such coupling within the array architecture during the design process and alter the feed network parameters to adjust for such coupling. Unfortunately, this is a nonlinear problem requiring special solution techniques. This report presents the solution techniques for determining feed network parameter values that compensate for antenna-feed network coupling. Scattering parameter representations of the antenna array and the feed networks are used. Examples of various array configurations for microstrip antenna arrays and for dipole arrays are included. / Master of Science

With higher frequencies now being used in RFID systems, antennas are becoming much smaller resulting in more space on tags that can be used for innovative array designs to harvest more wireless energy. This master's thesis outlines and details a new methodology for designing and simulating the staggered pattern charge collector, a technique to improve harvesting wireless energy. Staggered pattern charge collectors enable RFID tag's to produce a higher DC voltage from a charge pump circuit by creatively using multiple arrays to increase the antenna power conversion gain without limiting the half power beamwidth. This thesis discusses the basics of patch antennas and charge pumps as well as an optimization technique for the staggered pattern array by maximizing integrated power conversion gain (IPCG). An example of a staggered pattern charge collector is fully specified from design through simulation, in preparation for fabrication. This methodology allows for the staggered pattern charge collectors to be designed, simulated, and fabricated quickly and effectively.

The effect of mutual coupling between elements plays a crucial role to the performance of the antenna arrays. The radiation patterns of antenna arrays will be altered by the coupling effect from the adjacent elements thus reducing the accuracy and resolution in direction finding application. This research developed and validated the novel 3-D Algorithm to calculate the far-field pattern of dipole arrays arranged in three dimensions and in any configuration (both in straight and slanted position). The effect of mutual coupling has been accounted using the Induced EMF method. The computation is performed on 2x2 parallel dipoles and 12 dipoles arranged at the edge of a cube. The results are validated with other electromagnetic techniques such as Method of Moment (MoM) and Finite Difference Time-Domain (FDTD). Then, a 2x2 dipole array is chosen for beam steering and experiment validation due to its ease of implementation and feeding network. The array optimisation to control the pattern is performed using a genetic algorithm. The far-field pattern computed using the 3-D algorithm might be less accurate than other 3-D electromagnetic techniques but its array optimisation is faster and efficient. The simulation and measurement results are in good agreement with each other confirmed the validity of the 3-D algorithm.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2006. / This thesis investigates a computational model of an electronically steered antenna array. It focuses on a simple element comprising an S-shaped, crossed, cylindrical cavity-backed slot antenna. An unusual aspect of the element is the addition of a top hat, which contributes to the low scanning ability of the array. The objective was to confirm this contribution of the top hat. During the investigation, the computation code Feko was validated for slot analysis through consideration of the basic properties of a dipole and slot and how they related to each other. Various alternative models were evaluated, before a final accurate model was modelled in Feko, to find possible equivalent models. The final model, which implemented the use of Feko as release 5, was the only one that achieved successful results. The results showed that the top hat does play an important role in the steering of the beam. The mechanism through which this occurs was identified. The results that where obtained indicated that there may be more effective elements than the cylindrical element and the identification of this is proposed as a field for further study.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Worldwide, more large antenna arrays are being deployed in areas of science previously dominated by other antenna geometries. Applications for large arrays include Radar, Satellite Communications and Radio Astronomy. Even though the use of large arrays solve some of the difficulties posed by more traditional antennas, new challenges are also faced. One of these challenges is the problem of noise coupling, and how the overall system performance is affected by it. The Focal Plane Array (FPA), which is a new example of a large antenna array, is currently being researched at a number of institutions worldwide for use in Radio Astronomy. As a result, FPA’s were used as an example element to demonstrate the practical importance of this research. In this study, the effect of mutual coupling on the noise performance of FPA’s was illustrated. This was done by calculating the mutual coupling between the elements of the array, and then calculating the noise power received by each element as a result of the mutual coupling. Next, the Active Noise Figure and Active Noise Temperature were calculated. These parameters were introduced to visualise the effect of mutual coupling on the overall noise performance of the array. Since FPA’s are by definition large, conventional brute-force analysis techniques are very resource intensive. Solving the coupling terms using these methods therefore requires the use of computer clusters even during the design phase of the antenna, which is very expensive. A method was therefore developed to calculate the coupling terms of a large array using Periodic Boundary Conditions. The method uses infinite array analysis, which resulted in an improvement in memory usage in orders of magnitude. This improvement comfortably places the memory requirements for the analysis of large arrays within the range of current personal computers. The results also displayed a reasonable amount of accuracy for use during the design phase of an array. The additional noise power on each element as a result of mutual coupling were also calculated. This was achieved by developing an equivalent circuit diagram that represents the system in terms of the noise and transmission parameters of the LNA of each receiver channel, and the coupling terms of the antenna array. Lastly, the active noise temperature and active noise figure are calculated. The theory was implemented by means of a script with a graphical user interface, to provide easy-to-use access to the theory. A quick reference table of estimated noise coupling penalty versus first term coupling and LNA noise temperature was also compiled. The results of an example calculation showed a significant amount of noise coupling in an 8×8 Vivaldi array. The noise coupling resulted in an increase in system noise temperature, Tsys, in the order of 9% of the LNA noise temperature, TLNA. According to the SKA Tsys budget, this results in an approximate Tsys increase of 1.3 Kelvin. In the context of Radio Astronomy, this additional source of noise cannot be ignored, as it can greatly affect the usebility of the telescope for certain areas of research. / AFRIKAANSE OPSOMMING: Groot antennaskikkings word deesdae al hoe meer ingespan in plek van ander tradisionele antennamodelle. Toepassings vir groot antennaskikkings sluit Radar, Satellietkommunikasie en Radioastronomie in. Alhoewel die gebruik van groot antennaskikkings baie van die probleme wat deur ander tradisionele antennamodelle veroorsaak word oplos, word nuwe uitdagings terselfdertyd geskep. Een van hierdie nuwe uitdagins is ruiskoppelling en hoe dit die ruisgedrag van die stelsel as ’n geheel affekteer. ’n Beeldvlakskikking (FPA), is ’n opwindende nuwe voorbeeld van ’n groot antennaskikking en die moontlikheid vir die gebruik daarvan in radioastronomie word tans wêreldwyd nagevors. Om hierdie rede is die FPA gekies as voorbeeldelement om die bruikbaarheid van hierdie navorsing in die praktyk te beklemtoon. In hierdie studie word die effek van wedersydse koppelling op die ruisgedrag van FPA’s geïllustreer. Dit word gedoen deur eers die wedersydse koppelling tussen die elemente van die antennaskikking te bereken en dan die ruisdrywing wat deur elke element ontvang word as gevolg van wedersydse koppelling. Daarna word die Aktiewe Ruistal en die Aktiewe Ruistemperatuur bereken. Hierdie nuwe parameters word bekendgestel om die gevolge van wedersydse koppelling op die ruisgedrag van die stelsel as ’n geheel te visualiseer. Omdat FPA’s per definisie groot is, vereis die analise daarvan deur middel van konvensionele metodes baie rekenaar hulpbronne. Hierdie metodes vereis dus die gebruik van rekenaarbondels of superrekenaars selfs gedurende die ontwerpfase van die antenna, wat baie duur en onprakties is. Daar is dus ’n metode ontwikkel wat gebruik maak van periodiese randvoorwaardes om groot antennaskikkings te analiseer. Die metode benader ’n groot antennaskikking as ’n eindig-opgewekte oneindige skikking van antennas. As gevolg hiervan, word die geheueverbruik met ordegroottes verbeter. Hierdie verbetering plaas dus die analise van groot antennaskikkings binne die vermoëns van huidige persoonlike rekenaars. Die resultate wys ook ’n aanvaarbare graad van akkuraatheid vir gebruik gedurende die ontwerpfase van die skikking. Die bykomende ruisdrwying op elke element as gevolg van wedersydse koppelling is ook bereken. Om dit te vermag, is daar ’n ekwivalente stroombaandiagram ontwikkel wat die gekoppelde stelsel in terme van die ruis- en transmissieparameters van die laeruisversterker (LNA) aan elke ontvangerkanaal en die koppelterme van die antenna skikking voorstel. Laastens word die aktiewe ruistal en die aktiewe ruistermperatuur ook bereken. Die teorie is geïmplimenteer deur gebruik te maak van ’n grafiesegebruikerskoppelvlak (GUI). Die GUI verskaf aan die gebruiker maklike toegang tot die teorie wat onwikkel is in hierdie navorsing. Daar is ook ’n snelnaslaantabel geskep met benaderde waardes van ruiskoppelling vir ’n verskeidenheid waardes van LNA ruistemperature en eerste element koppelling. Die resultate van ’n 8×8 Vivaldiskikking voorbeeld, het ’n beduidende hoeveelheid ruiskoppelling getoon. Die ruiskoppelling het ’n maksimum toename in stelsel ruistemperatuur, Tsys, van ongeveer 9% van die LNA ruistemperatuur tot gevolg gehad. Volgens die huidige Tsys begroting van die SKA, kom dit neer op ’n Tsys toename van byna 1.3 Kelvin. In die konteks van die radioastronomie, kan hierdie toename in ruistemperatuur nie geïgnoreer word nie aangesien dit die bruikbaarheid van die teleskoop vir sekere velde van navorsing nadelig kan beïnvloed.

This thesis presents the design of radio-frequency (RF) tunable active inductors (TAIs) with independent inductance (L) and quality factor (Q) tuning capability, and their application in the design of RF tunable phase shifters and directional couplers for wireless transceivers. The independent L and Q tuning is achieved using a modided gyrator-C architecture with an additional feedback element. A general framework is developed for this Q- enhancement technique making it applicable to any gyrator-C based TAI. The design of a 1.5V, grounded, 0.13um CMOS TAI is presented. The proposed circuit achieves a 0.8nH-11.7nH tuning range at 2GHz, with a peak-Q in excess of 100. Furthermore, printed and integrated versions of tunable positive/negative refractive index (PRI /NRI) phase shifters, are presented in this thesis. The printed phase shifters are comprised of a microstrip transmission-line (TL) loaded with varactors and TAIs, which, when tuned together, extends the phase tuning range and produces a low return loss. In contrast, the integrated phase shifters utilize lumped L-C sections in place of the TLs, which allows for a single MMIC implementation. Detailed experimental results are presented in the thesis. As an example, the printed design achieves a phase of -40 to +34 degrees at 2.5GHz. As another application for the TAI, a reconfigurable CMOS directional coupler is presented in this thesis. The proposed coupler allows electronic control over the coupling coefficient, and the operating frequency while insuring a low return loss and high isolation. Moreover, it allows switching between forward and backward operation. These features, combined together, would allow using the coupler as a duplexer to connect a transmitter and a receiver to a single antenna. Finally, a planar electronically steerable patch array is presented. The 4-element array uses the tunable PRI/NRI phase shifters to center its radiation about the broadside direction. This also minimizes the main beam squinting across the operating bandwidth. The feed network of the array uses impedance transformers, which allow identical interstage phase shifters. The proposed antenna array is capable of continuously steering its main beam from -27 to +22 degrees of the broadside direction with a gain of 8.4dBi at 2.4GHz.

Approved for public release; distribution in unlimited. / a beam towards the UAV. A simulation model was developed and implemented in MATLAB programming language to study the effectiveness of beamforming using sensor clusters for establishing a communication link to the UAV. Results showed that the antenna main lobe remained relatively unchanged in the presence of position errors and sensor node failures or when the density of the sensor nodes changed. Additionally, the maximum average power gain of the main lobe can be increased by increasing the density of the sensor cluster, thereby increasing the transmission range between the sensor clusters and the UAV. / Civilian, Singapore Ministry of Defense

O presente trabalho trata do estudo, projeto, desenvolvimento, construção e medida de lentes discretas planares (DLAs). Estes dispositivos atuam como sistemas irradiantes, especialmente com características multi-feixes. A construção destas lentes utiliza tecnologias compatíveis com a fabricação de circuitos impressos, com alguns detalhes que são característicos da área de antenas e circuitos planares. O estudo aborda as equações de projeto e considerações gerais relativas ao atendimento de especificações técnicas preliminares. Foram desenvolvidas duas lentes discretas, uma na frequência de 8GHz (banda X) e outra na frequência de 40GHz (banda Ka- faixa de ondas milimétricas). São apresentados os resultados de medidas destas duas lentes, que comprovam a possibilidade de uso em aplicações multi-feixes, bem como seu efeito de foco, análogo ao observado em lentes óticas comuns. / The object of this work is the study, design, development, fabrication and measurement of discrete lens arrays (DLAs). These devices act as radiant systems, especially with multi-beam characteristics. Their construction follows the same procedures and techniques normally found in printed circuit fabrication, with some further details that are pertinent to the antenna and planar circuit field. This study contains the design equations and general remarks as to fulfill preliminary technical specifications. Two real designs were developed, one in the X-band (8GHz) and another in the millimeter range, Ka band (40GHz). Their respective measurement results are presented, which proved their possible application in multi-beam systems, as well as their focusing effect, which is analogous to that observed in common optical lenses.

This dissertation studies several problems centered around developing a better understanding of the energy efficiency of cooperative wireless communication systems. Cooperative communication is a technique where two or more nodes in a wireless network pool their antenna resources to form a "virtual antenna array". Over the last decade, researchers have shown that many of the benefits of real antenna arrays, e.g. spatial diversity, increased range, and/or decreased transmission energy, can be achieved by nodes using cooperative transmission. This dissertation extends the current body of knowledge by providing a comprehensive study of the energy efficiency of two-source cooperative transmission under differing assumptions about channel state knowledge, cooperative protocol, and node selfishness. The first part of this dissertation analyzes the effect of channel state information on the optimum energy allocation and energy efficiency of a simple cooperative transmission protocol called "orthogonal amplify-and-forward" (OAF). The source nodes are required to achieve a quality-of service (QoS) constraint, e.g. signal to noise ratio or outage probability, at the destination. Since a QoS constraint does not specify a unique transmit energy allocation when the nodes use OAF cooperative transmission, minimum total energy strategies are provided for both short-term and long-term QoS constraints. For independent Rayleigh fading channels, full knowledge of the channel state at both of the sources and at the destination is shown to significantly improve the energy efficiency of OAF cooperative transmission as well as direct (non-cooperative) transmission. The results also demonstrate how channel state knowledge affects the minimum total energy allocation strategy. Under identical channel state knowledge assumptions, the results demonstrate that OAF cooperative transmission tends to have better energy efficiency than direct transmission over a wide range of channel conditions. The second part of this dissertation focuses on the development of an opportunistic hybrid cooperative transmission protocol that achieves increased energy efficiency by not only optimizing the resource allocation but also by selecting the most energy efficient cooperative transmission protocol from a set of available protocols according to the current channel state. The protocols considered in the development of the hybrid cooperative transmission protocol include compress-and-forward (CF), estimate-and-forward (EF), non-orthogonal amplify-and-forward (NAF), and decode-and-forward (DF). Instantaneous capacity results are analyzed under the assumption of full channel state knowledge at both of the sources and the destination node. Numerical results are presented showing that the delay limited capacity and outage probability of the hybrid cooperative transmission protocol are superior to that of any single protocol and are also close to the cut-set bound over a wide range of channel conditions. The final part of this dissertation focuses on the issue of node selfishness in cooperative transmission. It is common to assume in networks with a central authority, e.g. military networks, that nodes will always be willing to offer help to other nodes when requested to do so. This assumption may not be valid in ad hoc networks operating without a central authority. This section of the dissertation considers the effect selfish behavior on the energy efficiency of cooperative communication systems. Using tools from non-cooperative game theory, a two-player relaying game is formulated and analyzed in non-fading and fading channel scenarios. In non-fading channels, it is shown that a cooperative equilibrium can exist between two self-interested sources given that the end of the cooperative interaction is uncertain, that the sources can achieve mutual benefit through cooperation, and that the sources are sufficiently patient in the sense that they value future payoffs. In fading channels, a cooperative conditional trigger strategy is proposed and shown to be an equilibrium of the two-player game. Sources following this strategy are shown to achieve an energy efficiency very close to that of a centrally-controlled system when they are sufficiently patient. The results in this section show that cooperation can often be established between two purely self-interested sources without the development of extrinsic incentive mechanisms like virtual currency.