<p>This report is introduced with a presentation of fundamental electromagnetic theories, which have helped a lot in the achievement of methods for calculation and design of microstrip transmission lines and circulators. The used software for the work is also based on these theories. </p><p>General considerations when designing microstrip solutions, such as different types of transmission lines and circulators, are then presented. Especially the design steps for microstrip lines, which have been used in this project, are described. Discontinuities, like bends of microstrip lines, are treated and simulated. There are also sections about power handling capability of microstrip transmission lines and different substrate materials. </p><p>In the result part there are computed and simulated dimensions of the microstrip transmission lines used in the prototype system. Simulations of conceivable loads in the cavity illustrate quantitatively the reflection coefficient. Even practical measurements are made in a network analyzer and are presentedin this part. </p><p>Suitable materials and dimensions for the final microwave feed transmission line system for high powers are then presented. Since circulators are included in the system a basic introduction to the design of these in stripline and microstrip techniques is also made. </p><p>At last conclusions, examinations of the designed system and comparisons to the today’s systems are made.</p>

In this thesis, a highly selective broadband hybrid bandpass filter operating between 0.4-2.0 GHz with a stopband up to 7 GHz is designed and analyzed. The realization is carried out by hybrid method, which combines both lumped and distributed element filters. In this approach, two separate filters, which are lumped highpass with 0.4 GHz corner frequency and distributed stripline lowpass with 2 GHz corner frequency, are combined to get the bandpass filter that has a passband in between 0.4 to 2.0 GHz. The usage of the lumped elements for the highpass filter resulted in a great size reduction compared to distributed element approach. The design software FILPRO&trade / is used to synthesize the trial filters. More than forty filters are synthesized, and among them, the ones that have better properties are chosen for further processes. Optimization, modeling and electromagnetic simulations of the selected lumped and distributed filters are carried out on the software GENESYS&trade / . Distributed filters are also simulated using the software SONNET&trade / . After the simulations, all of the simulated filters are realized and measured, and the level of consistency with the simulations is observed. According to the results of the measurements, the filter combination that has the best combination of low insertion loss, small dimensions, high stopband attenuation and low spur levels is selected for the final bandpass filter structure and a few variants are examined to get the final structure.

The aim of this thesis is to identify coupling mechanisms for three line microstrip, stripline and microstrip with dielectric overlay structures as either inductive or capacitive, quantify through simulation and measurement the amount of crosstalk to be expected in terms of scattering parameters. A new method of crosstalk suppression is implemented into each three line structure by placing uniformly spaced short circuits down the length of the center transmission line. All structures were simulated over various physical and electrical parameters. Select microstrip structures, shielded and unshielded, were fabricated and measured to validate the effectiveness of the shielding technique. Shielding effectiveness was calculated from the measurements, and their results showed that the isolation between lines was increased by up to 20dB.

Le but de ce travail était de développer des filtres passe-bande RF dans la technologie de PCB, avec trois objectifs principaux. Le premier objectif était de développer des formules de synthèse tosimplify la procédure de conception du filtre. Le deuxième était de parvenir à un rejet wideout bande sans modifier les caractéristiques de la bande de filtrage. Le troisième objectif est de contrôler la fréquence centrale du filtre en utilisant diode varicap. / The purpose of this work was to develop RF bandpass filters in PCB technology,with three main objectives. The first objective was to develop synthesis formulas tosimplify the design procedure of the filter. The second was to achieve wideout-of-band rejection without modifying the in-band filtering characteristics. Thethird objective was to control the center frequency of the filter by using varactordiode.The bandpass filter topology treated in this thesis is based on Stub-LoadedResonators (SLR). The main features of this filter topology were treated. Equivalentcircuits based on J-inverters and susceptance parameters were derived. Based onthese equivalent circuits, synthesis formulas were developed. Simulations werepresented to validate the synthesis theory. For a proof-of-concept, third orderstripline bandpass filters were designed and fabricated based on this synthesis.Analysis technique using odd- and even- mode was achieved on the SLR. Thusresonance odd- and even-mode conditions were derived. These conditions aim toeasily control the first spurious frequency. Moreover, to go further in improving theout-of-band rejection a new technique, called “U corner structure”, was developedand design rules were derived. Based on these design rules an extended out-of-bandrejection was achieved without any modification in the passband and by maintainingthe compactness of the filter. A first spurious frequency was localized at up to ninetimes the working frequency in the case of the Parallel-coupled Stub-Loadedresonator (PC-SLR) filter. Also, by applying this technique into the classicalparallel-coupled filter the first and second spurious frequencies were rejected. Toaddress the issue of tunable filters, the SLRs were correctly loaded by variablecapacitors (varactor diode). The center frequency of the PC-SLR filter was easilycontrolled by maintaining a large out-of-band rejection.

In this thesis, parametric study and design of Vivaldi antennas and arrays are studied. The parameters of single element antennas and arrays are investigated regarding their effects on the design. The return loss responses and radiation patterns are considered in the parametric study. The results of simulations realized using Ansoft HFSS, a high frequency electromagnetic field simulation program, are shown and discussed. Two different Vivaldi antennas operating in 8.5-10.5 GHz frequency band with return loss responses better than 15 dB are designed based on the results of parametric study. Stripline to slotline transition is used in the feeding section of both antennas. In the same manner, two different 8-element uniform linear arrays operating in 8.5-10.5 GHz with half power beam widths smaller than 12&amp / #730 / and side lobe levels smaller than 13 dB are designed. Binomial and Dolph-Chebyshev feeding techniques are also investigated in order to improve half power beamwidths and side lobe levels of the designed arrays. The designed single element Vivaldi antennas and a linear array of Vivaldi antennas are fabricated. The return loss response and radiation patterns of the fabricated antennas and the array are measured and compared with the simulation results.

This thesis focuses on planar filters operating at the circuit board level. Planar filters have gained increasing attention due to their low losses, wide bandwidths, and compact size, which are essential for modern communication systems. The introduction provides background information on the motivation for the study, along with its goals and research questions. Theoretical discussions cover fundamental aspects of filters, including an exploration of substrate properties such as FR-4, various transmission line types like microstrip, Stripline, and Suspended stripline, and the mathematics behind lumped element and distributed element filters. Different filter characteristics are considered, and a literature review examines previous methods, techniques, and software tools used for filter design to inform the methodology of this work.    Based on the literature review, CST (Computer Simulation Technology) and AWR (Applied Wave Research) are selected as software tools for simulation and design facilitation. An interdigital and a combline bandpass filter are used as references for a broadband filter. The study demonstrates that broader bandwidth filters can be achieved using high-pass and low-pass filters. Results present S-parameter data for simulated filters compared with fabricated and measured filters.   Simulation results indicate that Suspended stripline exhibits a wider bandwidth characteristic compared to microstrip. The fabricated and measured filters generally exhibit good agreement with simulation results, except for one case discussed in detail in section 6.2.1. The literature review and discussion also address the limitations of the FR-4 substrate for high-frequency applications and suggest alternative substrate types for this study.

Thesis (PhD (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Passive millimetre-wave (PMMW) imaging is a technique that uses radiometers to detect thermal radiation emitted and reflected by metallic and non-metallic objects. While visual and infra-red emissions are attenuated by atmospheric constituents, PMMW emissions are transmitted, resulting in consistent contrast between different objects from day to night in clear weather and in low-visibility conditions to form images for a range of security and inclement weather applications. The use of a PMMW imaging system on a small unmanned aerial vehicle (UAV) offers extremely attractive possibilities for applications such as airborne surveillance for search and rescue operations, which are often hindered by inclement weather making visibility poor and endangering the rescuers as the search vehicle flies through the bad weather zone. The UAV would fly above the bad weather zone, with the PMMW imaging system detecting the thermal radiation emitted and reflected by objects in the MMW spectrum through the inclement weather. The 35GHz propagation window is chosen for the greater transmission through atmospheric constituents. The design of the PMMW imaging system is severely limited by the size of the UAV, particularly in the inability to incorporate any form of optical or mechanical scanning antenna. A possible solution is a long, thin antenna array fitted under the wings of the UAV. Such an antenna has a narrow, high gain, frequency-scanned beam along the plane perpendicular to the flight path, but a very broad beam along the plane of the flight path blurs the image, making it difficult to accurately determine the position of an object or to differentiate between objects situated along the plane of the flight path. This dissertation proposes a technique of image reconstruction based on the Kalman filter, a recursive filter that uses feedback control to estimate the state of a partially observed non-stationary stochastic process, to reconstruct an accurate image of the target area from such a detected signal. It is shown that given a simulated target area, populated with an arbitrary number of objects, the Kalman filter is able to successfully reconstruct the image using the measured antenna pattern to model the scanning process and reverse the blurring effect / AFRIKAANSE OPSOMMING: Passiewe millimetergolf (PMMG) beeldvorming is ’n tegniek wat van radiometers gebruik maak om termiese straling waar te neem vanaf beide metaal en nie-metaal voorwerpe. Waar optiese en infra-rooi straling attenueer word deur atmosferiese bestanddele, plant PMMG strale ongehinderd voort. Dit lei tot konstante kontras tussen verskillende voorwerpe in daglig of snags, mooi of bewolkte weer, en in ander lae-sigbaarheid toestande om beelde te vorm vir ’n wye reeks sekuriteits- of weertoepassings. Die gebruik van PMMG beeldvorming op ’n klein onbemande lugtuig (OLT) bied aantreklike moontlikhede vir toepassings in observasie en reddingsoperasies, wat dikwels verhinder word deur bewolke weer wat reddingswerkers in gevaar stel as hul moet vlieg in toestande van lae sigbaarheid. Die OLT kan bokant die onweer vlieg, met die PMMG beeldvormer wat termiese straling in die millimetergolf spektrum vanaf voorwerpe kan waarneem in swaks weerstoestande. Vir verbeterde golfvoortplanting deur atmosferiese bestanddele, word die 35GHz band gekies. Die ontwerp van die PMMG stelsel word geweldig beperk deur die grootte van die OLT, spesifiek deur die tuig se onvermoë om ’n antenne te huisves wat opties of meganies kan skandeer. ’n Moontlike oplossing is om gebruik te maak van ’n lang, dun antenne samestelling wat onder die OLT se vlerke geplaas word. So ’n antenne het ’n nou, hoë-aanwins bundel wat met frekwensie skandeer langs ’n vlak loodreg tot die vlugtrajek. So ’n antenne het egter ’n baie wye bundel langs die vlugtrajek, wat beeldkwaliteit verlaag en dit moeilik maak om die posisie van ’n voorwerp langs die vlugtrajek te bepaal, of om tussen veelvuldige voorwerpe te onderskei. Hierdie proefskrif bied ’n tegniek van beeldherwinning gebaseer op die Kalman filter, ’n rekursiewe filter wat terugvoerbeheer gebruik om die toestand van ’n nie-stasionêre stochastiese proses af te skat wat slegs gedeeltelik waargeneem is, om soedoende ’n akkurate beeld van die teikenarea te herkonstrueer vanuit ’n verwronge beeld. Dit word getoon dat, gegewe ’n gesimuleerde teikenomgewing met ’n arbitrêre hoeveelheid voorwerpe, die Kalman filter suksesvol ’n beeld kan herkonstrueer deur gebruik te maak van die antenne se gemete stralingspatroon om die skanderingsproses na te boots, om sodoende die beeldkwaliteit te verhoog

Les circulateurs à ferrite sont des dispositifs essentiels et indispensables dans les chaînes de communication radiofréquences. Ils assurent l’aiguillage des signaux selon leur provenance, en favorisant la propagation de l’onde EM dans une direction plutôt que dans une autre. De ce fait, ils permettent de dissocier les signaux d’émission et de réception. Ils utilisent les propriétés d’anisotropie et de non-réciprocité des matériaux ferrites lorsque ces derniers sont aimantés par un champ magnétique statique. Leur mise au point s’avère assez délicate. D’un point de vue industriel, pour répondre à un cahier des charges, sont souvent obligés aujourd’hui de partir de designs existants qu’ils font évoluer « au coup par coup » grâce au savoir-faire de quelques spécialistes. Des réglages longs, fastidieux, et coûteux sont donc nécessaires et ils ne garantissent pas toujours une solution optimum. Il est en outre souvent difficile d’imaginer de nouveaux designs. Le principal but de ces travaux de thèse est de mettre au point une méthode de conception fiable permettant de prendre en compte les phénomènes physiques mis en jeu (perméabilité tensorielle, effets magnétostatiques, modélisation numérique robuste) afin d’obtenir des dispositifs opérationnels, sans réglage et aux performances optimisées. / Biased ferrite circulators have known a great technological progress, searching for fulfill the exponential growth of many new applications. Their operation is directly linked to the anisotropic characteristic of ferrite material to create non-reciprocity phenomenon. Their design remains quite complicated in view of several limitations of their high-frequency modelization. The main goal of this thesis is to establish a complete methodology which aims to take into account all the physical features related to such a device, to offer a reliable results with optimized performances and to minimize the post-tuning step which remains problematic for the industry of circulators.

The growth of flexible electronics industry has given rise to light-weight, flexible devices which have a wide range of applications such as wearable electronics, flexible sensors, conformal antennas, bio-medical applications, solar cells etc. Though several techniques exist to fabricate flexible devices, the limiting factors have been durability, cost and complexity of the approach. In this research, the focus has been on developing stretchable (flexible) conductors using a multi-layer structure of metal and conductive rubber. The stretchable conductors developed using this approach do not lose electrical connection when subjected to large strains up to 25%. Also, the conductivity of the conductive rubber has been improved by ~20 times using the multi-layer approach. Furthermore, the multi-layer approach was used to fabricate devices for RF and antenna applications. A flexible micro-stripline was fabricated using the multi-layer approach to study the performance at microwave frequencies up to 5 GHz. It was observed that using an optimal metal and conductive rubber layer structure can help to reduce the loss of the device by 58% and also the device does not get damaged due to bending. In addition to this, an aperture-coupled patch antenna at 3.1 GHz was fabricated using the multi-layer approach to demonstrate reconfigurability. Ideally, the multi-layer patch antennas can be stretched up to 25% which helps to tune the resonance frequency from 3.1 GHz to 2.5 GHz. The multi-layer patch antennas were tested up to ~10% strains to study their radiation properties. It was demonstrated that using an ideal multi-layer structure of metal and conductive rubber layer can help to improve the antenna's peak gain by 3.3 dBi compared to a conductive rubber based antenna.

Les développements récents des systèmes hyperfréquences conduisent à des contraintes drastiques sur la taille et le coût des composants, et en particulier sur les Filtres Passe-Bande (BPF). L’objectif de cette thèse était d’apporter des solutions innovantes pour du filtrage large-bande compact en basses fréquences. Nous avons proposé deux solutions topologiques de compacité.La première solution est axée sur l’amélioration de la compacité des résonateurs grâce au résonateur multi-sections. Cette topologie a été théorisée et modélisée afin de l’optimiser. La compacité apportée par le résonateur multi-sections a été démontrée à travers la réalisation de filtres interdigité. La deuxième solution est une nouvelle topologie du filtre combline appelée filtre combline à couplage électrique (ECC). Nous avons également montré que ces solutions topologiques sont compatibles avec d’autres solutions technologiques de compacité (multicouche…).Ces solutions permettent de résoudre les problèmes d’encombrement et d’intégration des filtres actuels tout en gardant des performances électriques équivalentes. / Recent developments in microwave systems lead to drastic constraints on the size and cost of components, and in particularly on Passband Filters (BPF). The aim of this thesis was to provide innovative solutions for low band compact broadband filtering. We proposed two topological solutions of compactness.The first solution focuses on improving the compactness of the resonator thanks to the multisections resonator. This topology has been theorized and modeled to optimize it. The compactness provided by the multi-sections resonator has been shown by the realization of interdigital filters. The second solution is a new topology of the combline filter, electrical coupling combline filter (ECC).We have also shown that these topological solutions are compatible with other technological solutions of compactness (multilayer ...).These solutions solve the size and integration problems of current filters with equivalentelectrical performance.