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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.

Reduced-control antenna arrays reduce the number of controls required for beamforming while maintaining a given array aperture. A reduced-control array for direction finding (DF), inspired by the concept of compressive sensing (CS), was recently proposed which uses random compression weights for combining antenna-element signals into fewer measurements. However, this compressive array had not been studied in terms of traditional characteristics such as directivity, sidelobe level (SLL) or beamwidth. In this work, random compression weights are shown to be suboptimal and a need for the optimisation of compressive arrays is expressed. Existing codebook optimisation algorithms prove to be the best starting point for the optimisation of compressive arrays, but are computationally complex. A computationally efficient codebook optimisation algorithm is proposed to address this problem, which inspires the compressive-array optimisation algorithm to follow. Compressive antenna arrays are formulated as a generalisation of reduced-control arrays and a framework is presented for their optimisation in terms of SLL. By allowing arbitrary compression weights, compressive arrays are shown to improve on existing reduced-control techniques. A feed network consisting of interconnected couplers and fixed phase shifters is proposed, enabling the implementation of compressive arrays in microwave hardware. The practical feasibility of compressive arrays is illustrated by successfully manufacturing a 3-GHz prototype compressive array with integrated antenna elements. / Thesis (PhD)--University of Pretoria, 2020. / Electrical, Electronic and Computer Engineering / PhD / Unrestricted

The use of phased array antennas in present day technology is limited, primarily due to the extremely high cost of implementation. This cost is contributed to the expense of phase shifters, which are the traditional method of beam steering in phased arrays. The need to alleviate this cost and avail the technology for commercial use necessitates study into alternative mechanisms for accomplishing beam steering. To this effect, this research is an exploration of one such mechanism. To characterize mutual coupling between microstrip patch antennas and explore its practicality as a feed mechanism, it is necessary to understand the factors controlling the phenomenon. A parametric study of the spacing between patch antennas and the consequent coupling is presented, the results of which are discussed in detail. further study into bandwidth extension and steer controlling techniques are also shown, with discussion on the practicality and future of the mechanism as a candidate for widespread application.

Dans le cadre de cette thèse, on s'intéresse dans un premier temps à des matrices d'alimentation de type passif connues qui permettent de produire des faisceaux orthogonaux, et notamment à la matrice de Butler. On s'aperçoit qu'il n'existe qu'une méthode itérative permettant de déterminer les paramètres S d'une matrice de Butler symétrique. C'est pourquoi, on cherche à déterminer de manière analytique la matrice [S] d'une matrice de Butler symétrique à N = 2^n entrées et N sorties. On établit des formules de récurrence issues de l'étude de ce type de matrices pour plusieurs tailles. Des formules analytiques en sont déduites qui sont valables quelle que soit la valeur de N. On poursuit l'étude des matrices d'alimentation de réseau d'antennes en s'intéressant à la source focale d'une antenne multifaisceaux devant réflecteur basée sur une géométrie originale constituée de coupleurs directionnels tridimensionnels entrelacés. Cette structure est simulée. Ses nombreux paramètres sont optimisés afin d'aboutir à une solution répondant au cahier des charges. Une maquette est réalisée et testée. Les résultats obtenus sont prometteurs. Au final, cette source possède l'avantage d'avoir un fort niveau de réutilisation de ses éléments rayonnants et donc de limiter l'encombrement du système global qui est souvent un point critique, dans les satellites notamment. Pour finir, on s'intéresse à une structure dont le but est d'avoir une station au sol capable de suivre une cible sans dépointage. La poursuite en azimut est assurée par une partie mécanique, de type joint tournant ; celle en élévation par un module électronique. Le système se doit d'être compact, fiable, et de limiter les pertes ainsi que les coûts. Des compromis sont donc à effectuer. La partie rayonnante est réalisée en guide, la partie alimentation en technologie planaire. Une solution est proposée afin de faire la transition entre ces deux technologies : le circuit de répartition est directement relié à l'excitation des éléments rayonnants en mettant ces deux parties sur une même feuille de substrat. Ainsi, moins de câbles et de connecteurs sont nécessaires, ce qui diminue l'encombrement et les coûts. / In this PhD thesis, some feed networks are studied. First, a N x N symmetric Butler matrix is considered. Analytical formulas allowing constructing its [S] matrix are found and demonstrated. Second, a multibeam antenna focal array based on 3-D directional couplers is considered. This device has a high level of re-use of its radiating elements. Therefore, its global size is reduced. Its conception is explained. Measurement results are exposed. Last, a mechanic / electronic device is studied. It is used for tracking. It is a complex device with several parts. The fact that the conception of each part depends on each other is highlighted. Compromises and choices need to be made.

[ES] Esta tesis aborda temas de especial interés en el diseño de antenas en la banda de milimétricas. Hui en dia, implementar components passius per a operar en la banda de mil·limètriques i assegurar el contacte i l'alineament metàl·lic apropiat entre peces, resulta un desafiament complex. Habitualment les línies de transmissió i les guies d'ones metàl·liques són les solucions adoptades, però en el primer cas es presenten pèrdues al ser solucions impreses i en el segon cas un mal contacte metàl·lic comporta fugues de camp. Per tant, s'estan explorant nous conceptes que solucionen estos problemes. La tecnología Gap Waveguide (GW) resulta adecuada ya que no requiere de contactos metálicos. En los últimos años han surgido las agrupaciones de antenas basadas en la tecnología Gap Waveguide y son un candidato prometedor para satisfacer algunas de las necesidades mencionadas. La tecnología GW ha demostrado ser atractiva para dispositivos de milimétricas porque permite redes de distribución completamente metálicas de una manera más simple que las guías de onda convencionales. Por tanto, estas redes tienen muy bajas pérdidas pero además son simples de fabricar. Esto es posible gracias a la capacidad de las GW de confinar de forma segura la propagación de ondas electromagnéticas por medio de una estructura que no requiere de contacto. Durante la última década, se han hecho avances importantes en la tecnología GW y en la literatura se pueden encontrar un buen número de antenas basadas en GW. Esta tesis va un paso más allá en la contribución de este tipo de antenas. Aquí, no solo se presentan antenas con polarización lineal, como suelen ser las desarrolladas hasta ahora, sino también con polarización dual, circular y duales en banda. Estas aportaciones son especialmente atractivas dentro del campo de las comunicaciones por satélite en movimiento (SATCOM on-the-move). Además, se han explorado nuevas redes de distribución que permiten antenas planas más compactas, más ligeras. / [CAT] Esta tesi aborda temes d'especial interés en el disseny d'antenes en la banda de mil.limètriques. Hui en dia, implementar components passius per a operar en longituds d'onda tan xicotetes (de l'orde de mil.límetres) i assegurar el contacte i l'alineament metàl-lic apropiat entre peces, resulta un desafiament complex. Habitualment les línies de transmissió i les guia d'ones metàl.liques són les solucions adoptades, però en el primer cas es presenten pèrdues al ser solucions impreses i en el segon cas un mal contacte metàl.lic comporta fugues de camp. Per tant, s'estan explorant nous conceptes que solucionen estos problemes. La tecnologia Gap Waveguide (GW) resulta adequada ja que no requerix de contactes metàl.lics. En els últims anys han sorgit les agrupacions d'antena basades en la tecnologia Gap Waveguide i són un candidat prometedor per a satisfer algunes de les necessitats mencionades. La tecnologia GW ha demostrat ser atractiva per a dispositius de banda d'ones mil-limètriques perquè permet xarxes de distribució completament metàl-liques d'una manera més simple que les guies d'onda convencionals. Per tant estes xarxes tenen baixes pèrdues peró, a més, són simples de fabricar. Açò és possible gràcies a la capacitat de les GW de confinar de forma segura la propagació d'ones electromagnètiques per mitjà d'una estructura que no requerix de contacte. Durant l'última dècada, s'han fet avanços importants en la tecnologia GW i en la literatura es poden trobar un bon nombre d'antenes basades en GW. Esta tesi va un pas més enllà en la contribució d'este tipus d'antenes. Ací, no sols es presenten antenes amb polarització lineal com solen ser les desenrotllades fins ara, sinó també antenes amb polarització dual, circular i inclús antenes duals en banda. Estes aportacions són especialment atractives dins del camp de les comunicacions per satèl.lit en moviment (SATCOM on-the-move). A més també s'han explorat noves xarxes de distribució que permeten obtindre antenes planes més compactes, més lleugeres. / [EN] This thesis deals with topics of special interest regarding the design of antennas at the mm-wave band. Today, implementing passive components that operate in the mm-wave band and to ensure the appropriate metallic contact is challenging. Commonly, conventional planar transmission lines and hollow metallic waveguides are the usual solutions but they present high losses or they do not ensure a good metallic contact. So, new concepts must be explored. Gap Waveguides (GWs), result suitably since they do not require metallic contact for shielding. Antenna arrays in Gap Waveguide Technology (GW) emerges as one promising candidate to naturally meet some of the mentioned needs. GW technology has demonstrated to be effective for mm-wave band devices because it enables full-metal distribution networks in a much simpler way than conventional waveguides. Very low distribution losses can be achieved preserving at the same time the assembly simplicity of multilayer microstrip feeding networks. This unique feature is a consequence of gap waveguides ability to safely confine the electromagnetic wave propagation through a contactless structure. During the last decade, there have been important advances in GW technology and a good number of gap waveguide-based arrays can be found in the literature. This thesis goes a step further in the contribution to mm-wave gap waveguide antennas. Here, antennas with linear polarization as well as circular or dual polarization are proposed. Dual band antennas has also been explored. These contributions have been carried out with a focus on satellite communications on-the-move. In addition, new distribution networks have also been explored to obtain more compact, low-profile and lighter antennas. / Ferrando Rocher, M. (2018). Gap Waveguide Array Antennas and Corporate-Feed Networks for mm-Wave band Applications [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/115933 / TESIS