Thesis (MS)--Montana State University--Bozeman, 2010. / Typescript. Chairperson, Graduate Committee: Brock LaMeres. Includes bibliographical references (leaves 92-96).

Thesis (Master of Engineering in Electrical Engineering)--Cape Peninsula University of Technology, 2018. / This research report discusses feasible designs of conformal antennas that provide a proof of concept for the French South African Institute of Technology’s future needs. The design is to be used in forthcoming space missions and the intention is to mount the antenna on the surface of a spacecraft. Hence, a low profile is mandatory along with good circular polarisation radiation characteristics. Microstrip patch antennas have been chosen for this purpose simply because they have low profile and conform to most structures, thus fulfilling the requirements stated above. All the designs that are featured in this thesis were modelled and validated using the electromagnetic simulation software FEKO and prototypes were built and tested. The simulations and measured results are supplemented by theory. Sometimes it can be challenging to design and develop an antenna that fulfils the required performance goals given the size and weight restrictions that are specified for nano-satellite technology. Therefore, the first phase of this project finds a good balance between the criteria set for CubeSat platforms and antenna performance. The second phase is validation. Single patch antennas and a sequential rotated patch array were designed, built and tested. The sequential rotated patch array offers considerable improvements in performance when compared to single patch antennas. For instance, the 3 dB axial ratio bandwidth increased to 9.6 % from 2 % when a sequential rotated array was used. The CubeSat normally flies in the inclined regions of the low Earth orbit (LEO). This area has high-energy auroral electron fluxes, in which the high-density electrons build up on ungrounded surfaces of spacecraft and cause discharge arcing. The discharge can affect the satellite operation and, in the worst case, cause permanent damage to the components. A mitigation technique by means of a bleeding path provides a quick route to ground and the space-qualified material that is used will ensure that the antenna is robust enough to survive this.

Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology, 2009 / This thesis presents the design, analysis and implementation of an eight-element phased array antenna for wideband X-band applications. The microstrip phased array antenna is designed using eight quasi-Yagi antennas in a linear configuration and is printed on RT/Duroid 6010LM substrate made by Rogers Corporation. The feeding network entails a uniform beamforming network as well as a non-uniform -25 dB Dolph-Tschebyscheff beamforming network, each with and without 45° delay lines, generating a squinted beam 14° from boresight. Antenna parameters such as gain, radiation patterns and impedance bandwidth (BW) are investigated in the single element as well as the array environment. Mutual coupling between the elements in the array is also predicted. The quasi-Yagi radiator employed as radiating element in the array measured an exceptional impedance bandwidth (BW) of 50% for a S11 < -10 dB from 6 GHz to 14 GHz, with 3 dB to 5 dB of absolute gain in the frequency range from 8 GHz to 11.5 GHz. The uniform broadside array measured an impedance BW of 20% over the frequency band and a gain between 9 dB to 11 dB, whereas the non-uniform broadside array measured a gain of 9 dB to 11 dB and an impedance BW of 14.5%. Radiation patterns are stable across the X-band. Beam scanning is illustrated in the E-plane for the uniform array as well as for the non-uniform array.

The principal contributions of this study include the development of a new capacitive feeding mechanism for wideband probe-fed microstrip patch antennas as well as the implementation of a spectral-domain moment-method formulation for the efficient analysis of large, but finite arrays of these elements. Such antenna configurations are very useful in the wireless communications industry, but extremely difficult to analyse with commercially available software. Probe-fed microstrip patch antennas have always been a popular candidate for a variety of antenna systems. Due to their many salient features, they are well suited for modern wireless communication systems. However, these systems often require antennas with wideband properties, while an inherent limitation of probe-fed microstrip patch antennas is its narrow impedance bandwidth. This can be overcome by manufacturing the antenna on a thick low-loss substrate, but at the same time it also complicates things by rendering the input impedance of the antenna very inductive. In this thesis, a new capacitive feeding mechanism is introduced that can be used for probe-fed microstrip patch antennas on thick substrates. It consists of a small probe-fed capacitor patch that is situated next to the resonant patch. The benefits of this configuration include the fact that only one substrate layer is required to support the antenna. It is also very easy to design and optimise. The use of full-wave methods for an accurate analysis of microstrip antennas, has basically become standard practice. These methods can become very demanding in terms of computational resources, especially when large antenna arrays have to be analysed. As such, this thesis includes a spectral-domain moment-method formulation, which was developed for the analysis of probe-fed microstrip patch antennas or antenna arrays that comprise of the new capacitive feeding mechanism. Here, entire-domain and subdomain basis functions are combined in a unique way so as to minimise the computational requirements, most notably computer memory. It is shown that, for general antenna array configurations, memory savings of more than 2500 times can be achieved when compared with typical commercial software packages where only subdomain basis functions are used. Some of the numerical complexities that are dealt with, include various methods to evaluate the spectral integrals as well as special algorithms to eliminate the recalculation of duplicate interactions. The thesis also contains a quantitative comparison of various attachment modes that are often used in the moment-method modelling of probe-to-patch transitions. Various numerical and experimental results are included in order to verify the spectral-domain moment-method formulation, to characterise the new feeding mechanism and to illustrate its use for various applications. These results show that, in terms of accuracy, the spectral-domain moment-method formulation compares well with commercial codes, while by comparison, it demands very little computer memory. The characterisation results show that the input impedance of the antenna can be fully controlled by only adjusting the size of the capacitor patch as well as the width of the gap between the capacitor patch and the resonant patch. In terms of applications, it is shown how the new antenna element can effectively be employed in linear arrays with vertical polarisation, horizontal polarisation or dual slant-polarisation. These represent some widely-used configurations for modern base-station antennas. / Thesis (PhD (Electronic Engineering))--University of Pretoria, 2005. / Electrical, Electronic and Computer Engineering / unrestricted

This dissertation investigates a simple LC-matching network for the impedance bandwidth enhancement of microstrip patch antennas. Wideband impedance matching is a standard practice for active circuits. Simple impedance matching of antennas is also quite common, but data on wideband impedance matching of antennas is not found very much in the open literature. The matching circuit presented consists out of a resonant LC-circuit with a quarterwave matching line as part of the design. Results for a number or experimental antennas, on which the new technique was applied, are included in the report. A well-defined design procedure is also presented, and results in a relatively small circuit to implement. It is shown that the antenna VSWR bandwidth could be improved to more than double the original size in most of the antennas investigated. / Dissertation (M Eng (Electronic Engineering))--University of Pretoria, 2006. / Electrical, Electronic and Computer Engineering / unrestricted

The Mini-Numerical Electromagnetic Code (MININEC) program, a PC-Compatible version of the powerful NEC program, is used to design a new type of reduced-size antenna. The validity of the program to model simple well-known antennas, such as dipoles and monopoles, is first shown. More complex geometries such as folded dipoles, and meander dipole antennas are also analysed using the program. The final design geometry of a meander folded dipole is characterized with MININEC, yielding results that serve as the basis for the practical construction of the antenna. Finally, the laboratory work with a prototype antenna is described, and practical results are presented.

In this research we attempted several modifications to microstrip ring/loop antennas to design multi-frequency antennas through systematic approaches. Such multi-frequency antennas can be useful while building compact terminals to operate at multiple wireless standards. One of the primary contributions was the use of a capacitive feed arrangement that enables simultaneous excitation of multiple concentric rings from an underlying transmission line. The combined antenna operates in the same resonant bands as the individual rings and avoids some of the bands at harmonic frequencies. A similar feeding arrangement is used to obtain dual band characteristics from just one ring, with improved bandwidth. This is made possible by widening two adjacent sides of a square ring antenna symmetrically, and attaching an open stub to the inner edge of the side opposite to the feed line. Use of fractal segments replacing the side with the stub also results in a similar performance. Use of fractal geometries has been widely associated with multi-functional antennas. It has been observed from the parametric studies that, the ratio of the resonant frequencies can range from 1.5 to 2.0. This shows some flexibility in systematically designing dual-band antennas with a desired pair of resonant frequencies. An analysis technique based on multi-port network modeling (MNM) has been proposed to accurately predict the input characteristics of these antennas. This approach can make use of the ordered nature of fractal geometries to simplify computations. Several prototype antennas have been fabricated and tested successfully to validate simulation and analytical results.

Cette thèse présente de nouveaux développements pour de petites antennes en cavité. L'objectif principal de la thèse est l'analyse de la performance de la bande passante de ces antennes pour des tailles d'ouverture qui sont petites par rapport à la longueur d'onde en espace libre. Des cavités de formes rectangulaires et circulaires intégrées dans un plan de masse infini et dans des plans de masse de dimensions latérales finies sont examinées en détail. Jusqu'à présent, dans la littérature, le choix pour ces antennes en cavités portait sur des antennes imprimées microruban (patch). L'objet de la thèse est de déterminer si les performances d'antennes en cavité de petite taille peuvent être améliorées et si oui, de quelle façon. A cet effet, nous avons tout d'abord étudié théoriquement, la limite supérieure de la bande passante pour cette configuration particulière en cavité. Nous en avons conclu que les antennes microruban intégrées dans une cavité n'atteignent pas la limite de la bande passante, ce qui est l'un des principaux résultats de la thèse. Les antennes intégrées dans une cavité avec un plan de masse infini ou fini sont ensuite analysées à l'aide de plusieurs modèles de ligne de transmission simples. Le deuxième résultat clé de la thèse un modèle de ligne de transmission spécifique et original qui montre que cette limite sur la bande passante est réellement atteignable. Par conséquent, ce modèle de ligne de transmission devient la base d'une nouvelle conception pour l'antenne en cavité. Enfin, le résultat le plus important de la thèse est la conception concrète de nouvelles antennes en cavité capables d'atteindre la performance maximale en bande passante. D'autres sujets sont abordés sont: i) la comparaison avec des structures à base d'éléments empilés en termes de bande passante, de facilité de fabrication et de coût, ii) l'extension de la limite grâce à l'inclusion de matériaux magnétiques idéaux et conducteurs magnétiques; iii) l'utilisation de la nouvelle structure d'antenne pour la constitution d'un réseau d'antennes compact; iv) les avantages de la nouvelle structure pour la réalisation d'antennes en cavité de tailles vraiment petites pour lesquelles les méthodes classiques ne permettent pas la réalisation d'antennes. / This thesis presents new developments in cavity type antennas. The main objective of the thesis is bandwidth performance analysis of antennas in cavities with aperture sizes which are small compared to the free space wavelength. Cavities of rectangular and circular shapes in an infinite and finite ground plane are investigated in detail. So far in the literature, microstrip patch antennas were the antenna of choice for cavity type antennas. The intention of the thesis is to determine if cavity type antennas can be improved and how. To this end, the bound on bandwidth for cavity antennas is investigated theoretically. It is concluded that patch antennas, in fact, do not reach the bound for cavity antennas, which is one of the key results of the thesis. Infinite and finite sized ground plane cavity antennas are further analyzed using several simple transmission line models. The second key result of the thesis is a demonstration that a special transmission line model corresponds to antennas that reach the bound on bandwidth. This transmission line model is the basis to a new cavity antenna design. Finally, the most important result is a practical, physical, design of novel cavity antennas capable of reaching the bandwidth bound. Furthermore, several additional topics are explored; i) A comparison with stacked patches design in terms of bandwidth, ease of fabrication, and cost; ii) The extension of the bound with the inclusion of ideal magnetic materials and magnetic conductors; iii) The new antenna design use in constructing a compact antenna array; iv) The benefits of the new design for constructing small cavity antennas previously not feasible with the classical design.

Antennas in hand-held radios must be compact and unobtrusive. Electrically small and low-profile antennas experience high input reactance, low input resistance, and low radiation efficiency.Further degradation of radiation efficiency occurs in hand-held radios due to size-reduced ground planes, losses within the plastic device casing, and losses due to coupling with the tissue of the user. These factors may also affect the radiation pattern of the antenna. This discussion reports on antenna designs that are well suited for hand-held radios. The design issues are covered for electrically small antennas and the hand-held environment. A review of Microstrip Antenna (MSA) theory, and the theory of the Inverted-L Antenna (ILA), and variations on the ILA including the Inverted-F Antenna (IFA), Planar Inverted-F Antenna (PIFA), and Dual Inverted-F Antenna (DIFA) is included. Two specific antenna designs are presented: the DIFA and the Proximity-Coupled Rectangular Patch MSA. The radiation patterns and input impedance of the DIFA are calculated numerically and measured empirically. The Proximity-Coupled Rectangular Patch Microstrip Antenna is treated numerically. / Master of Science

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