A theoretical and experimental investigation into the use of the corrugated circular waveguide as a feeder and radiator for microwave antennas is described. Because corrugated waveguide feeders are ·overmoded, the effects on the propagation and radiation characteristics of mode conversion due to bends are investigated. New methods of providing higher order mode suppression are described, and substantiated by experimental results using resonant cavity and transmission line methods. The cross-polarisation properties of corrugated waveguides are shown to be intrinsically superior to those of smooth wall waveguides when the waveguide wall suffers elliptical deformation. As an alternative to the problems involved in overmoded operation a design of corrugated circular waveguide for HEll mono-mode operation, which still exhibits an attenuation advantage, is developed. The radiated co-polar and cross-polar performance of corrugated circular waveguides and narrow flare-angle corrugated concial horns are studied both experimentally and theoretically using a more accurate analysis than attempted by previous authors. Design curves for optimum cross-polar radiation performance are presented and a new method of improving the cross-polarisation performance of these structures is theoreti6ally predicted, and experimentally verifjed.

The characteristics of slotted circular waveguides with different dimensions, including cutoff frequencies of TE and TM modes, impedance and modal field distributions will be analyzed using the generalized spectral domain approach. The Method of Moment will be applied, basis functions that include the edge conditions will be used and a computer program will be developed. Obtained results will be presented for different number, depth and thickness of coupling slots, and compared with available data to demonstrate the accuracy and the efficiency of the approach. Plots of the electric and magnetic field lines corresponding to the dominant as well as a number of higher order modes will be presented for quadruple ridge case.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The aggressive space mapping algorithm is used in this project for the optimisation of electromagnetic structures. This technique combines the use of fast, less accurate models with more time-consuming, high precision models in the optimisation of a design. MATLAB’s technical computing environment possesses powerful tools for optimisation as well as the graphical representation and mathematical post-processing of data. A software interface, which uses Visual Basic for Applications, is created between MATLAB and the electromagnetic solvers, CST Microwave Studio and μWave Wizard, that are used for the fine and coarse model calculations. The interface enables the direct interchange of data, which allows MATLAB to control the optimisation for the automation of the design process. The optimisation of a microwave coaxial resonator with input coupling is used to demonstrate the design environment. An accurate equivalent circuit model is available to describe the problem. The space mapping optimisation of this structure works well, with a significant improvement in the efficiency of the optimisation when compared to standard optimisation techniques. Multimode horn antennas are of interest for use as feeds in radio-astronomy telescope systems. The design of a stepped circular horn antenna in the space mapping design environment is presented. The horn’s radiation pattern is optimised for low cross-polarisation. This structure is much more complex to model than the resonator example. The generalised scattering matrix representation is used in the coarse model description. The far-fields are calculated from the aperture fields by means of the Fast Fourier Transform. Various tests confirm that the optimisation is steered in the right direction as long as the coarse model response follows the trend of the fine model response over the optimisation space. The presented design environment is a powerful tool for the automation of the design of electromagnetic structures. / AFRIKAANSE OPSOMMING: Die aggressiewe ruimte-afbeelding algoritme word in hierdie projek gebruik vir die optimering van elektromagnetiese strukture. Hierdie tegniek kombineer die gebruik van vinnige, minder akkurate modelle tesame met tydrowende hoë presisie modelle tydens die optimering van ’n ontwerp. MATLAB se tegniese verwerkingsomgewing beskik oor kragtige gereedskap vir optimering sowel as die grafiese voorstelling en wiskundige verwerking van data. ’n Sagteware koppelvlak, wat Visual Basic for Applications benut, word geskep tussen MATLAB en die elektromagnetiese oplossers, CST Microwave Studio en μWave Wizard, wat vir die fyn en growwe model berekeninge gebruik word. Hierdie koppelvlak maak die direkte uitruiling van data moontlik, wat MATLAB in staat stel om die optimering te beheer ten einde die ontwerpsproses te outomatiseer. Die optimering van ’n mikrogolf koaksiale resoneerder met intree koppeling word gebruik om die ontwerpsomgewing te demonstreer. ’n Akkurate ekwivalente stroombaanmodel is beskikbaar om die probleem mee te beskryf. Die ruimte-afbeelding optimering van hierdie struktuur werk goed en toon ’n aansienlike verbetering in die doeltreffendheid van die optimering wanneer dit met standaard optimeringstegnieke vergelyk word. Multimodus horingantennes is van belang in radio-astronomie, waar dit as voere vir teleskope gebruik word. Die ontwerp van ’n trapvormige, sirkelvormige horingantenne in die ruimte-afbeelding ontwerpsomgewing word aangebied. Die stralingspatroon van die horing word optimeer vir lae kruispolarisasie. Hierdie struktuur is heelwat meer ingewikkeld om te modelleer as die resoneerder voorbeeld. Die veralgemeende strooimatriks voorstelling word gebruik in die growwe model beskrywing. Die ver-velde word bereken vanaf die velde in die bek van die antenne, deur gebruik te maak van die Vinnige Fourier Transform. Verskeie toetse bevestig dat die optimering in die regte rigting gestuur word, solank as wat die growwe model se gedrag dié van die fyn model oor die optimeringsgebied navolg. Die ontwerpsomgewing wat hier aangebied word, is ’n kragtige stuk gereedskap vir die outomatisering van die ontwerp van elektromagnetiese strukture.

Abstract The purpose of this task is to synthesize a dielectric substrate material through a sintering process, which can be used for non-invasive physiological sensor development. Low loss, high dielectric constant ceramic material is used. Sintering process is employed to ensure stable structure and homogeneous dielectric properties of the substrate. Samples were prepared with TiO2 and in combination with CuO and Al2O3. All samples were measured and validated in 500 MHz to 20 GHz frequency range. Characterization measurements were performed with a Vector Network Analyzer, FieldFox N9918A, and connected to Keysight, open ended coaxial probe and performance probe. Reflection based measurement method was used due to its simplicity, speed and requirement of wideband data. The dielectric measurement results of developed samples show non-frequency dispersive behaviour, high dielectric constant and data was also selected at 2.45 GHz in aligned to the industrial, scientific and medical band. The resulting measurements show the highest dielectric constant of 16.6 at 2.45 GHz with a very low loss behaviour. / Målet är att syntetisera ett material, genom sintringsprocess, som kan användas som ett dielektriskt substrat för utveckling av sensorer. Det dielektriska materialet har keramisk materialstruktur och innehar högt dielektricitetskonstant med låga dielektriska materialförluster. Denna uppgift kräver att dielektriska materialet ska vara stabilt och inneha isotropiska egenskaper efter att genomgått sintringsprocess. Proverna förberedes med TiO2 och även i kombination med TiO2 tillsammans med CuO och Al2O3. Proverna mäts i frekvensområdet 500 MHz till 20 GHz. Mätningarna utförs med Vector Network Analyzer, FieldFox N9918A från Keysight. Resultat som visas och jämförs i arbetet är tagna vid 2.45 GHz eftersom det används och är standardiserat för medicinskt frekvensband. Högsta uppmätta dielektricitetskonstant har värdet av 16,6. Resultaten visar även låga förluster i dielektrikumet.

В данной работе представлены исследования характеристик металлического круглого волновода с неоднородным диэлектрическим заполнением и одномодового оптического волокна. Были построены и проанализированы частотные зависимости постоянной распространения для следующих диэлектрических структур круглого волновода: стержень, втулка, цилиндр, цилиндр с зазором, стержень с параболическим профилем изменения относительной диэлектрической проницаемости. Были рассмотрены одномодовые оптические волокна с разным профилем преломления и изучены материальная и хроматическая дисперсия одномодового волокна. / This work contains researches of characteristics of inhomogeniously filled metal circular waveguide and single-mode optical fiber. Frequency dependences of propagation constant of following dialectic structures in circular waveguide were calculated and analyzed: rod, plug, cylinder, cylinders with air gap, rod with parabolic permittivity profile. Characteristics of single-mode optical fiber with different refractive index profiles were considered, alsomaterial and chromatic dispersions were explored.

Il est bien connu dans la théorie de Maxwell que le rayonnement électromagnétique (EM) d'une onde porte à la fois du moment linéaire (énergie) et du moment angulaire. Ce dernier possède deux parties: le Moment Angulaire de Spin (ou SAM) qui est également connu sous le nom de la polarisation et le Moment Angulaire Orbital (ou OAM). Le SAM ne comprend que deux états (gauche et droite) et est utilisé en télécommunications pour doubler la capacité du canal. Par contre, le moment angulaire orbital (OAM) peut en théorie, avoir un nombre infini d'états appelés les modes OAM. Par conséquent, en radiofréquences, les premières applications de l'OAM ont été proposées dans le domaine des communications sans fil. Mais, tout d'abord, il est nécessaire de développer des antennes générant de telles ondes. L'objectif de cette thèse est de concevoir des antennes pour générer des ondes ayant un OAM. Le manuscrit se décompose en trois parties. Dans la première partie, un réseau d'antennes « patches » utilisant un déphaseur original est développé et testé. Ce réseau génère une onde ayant de l'OAM. Dans la deuxième partie, une cavité Fabry-Perot (FP) est utilisée pour apporter plus de directivité à ce réseau d'antennes. Enfin, la troisième partie consiste à générer des ondes guidées possédant du moment OAM. Ces ondes ont ensuite été utilisées pour exciter des antennes en cornet et rayonner des faisceaux directifs transportant du moment angulaire orbital. / It is well known from Maxwell’s theory that electromagnetic (EM) radiation carries both linear momentum (energy) and angular momentum. The latter has two parts: Spin Angular Momentum (SAM) which corresponds to the polarization of an EM wave and Orbital Angular Momentum (OAM) which is associated with the spatial distribution of an EM wave. The SAM has only two states (left and right) and is used to double the channel capacity in telecommunications. On the other hand, the OAM can theoretically have an infinite number of states called the OAM modes. Therefore, the first applications of OAM have been proposed in wireless communications at radio frequencies. However, first of all, it is necessary to develop the antennas for generating such waves. The objective of this thesis is to design the antennas for the generation of radio waves bearing OAM. The manuscript contains three parts. In the first part, an antenna using 4 patches and an original phase shifter is developed and tested to generate an OAM wave. In the second part, a Fabry-Perot (FP) cavity is used to enhance the directivity of this antenna. The third part is to generate guided OAM waves. Some horn antennas are used to radiate these waves with good directivity.