No description available.

In an effort to determine if there is a specific conformational structure which is most effective at the appropriate active physiological site, the synthesis of a group of sterically restricted analogs was undertaken. A portion of the polymethylene carbon skeleton of glutaric acid was replaced by selected aromatic carbons in benzenedicarboxylic acids to produce a series of ridged conformers, and the relative plant growth regulating properties of these derivatives were determined.

It is known that the 1-18 GHz Double Ridge Guide Horn (DRGH) antenna is highly sensitive to tolerances in manufacturing. Since a typical DRGH antenna is constructed from a number of individual parts, tolerances in the machining, even when numerically controlled, and errors in the assembly can easily lead to gaps between subsections. Performance deviations, most notably resonances in the boresight gain and VSWR was observed in a number of manufactured 1-18 GHz DRGH antennas. The exact cause of the performance deviations had to be determined in order to identify which sections of the antenna need to be redesigned in such a way that the effects of the manufacturing and assembling tolerances on the performance of typical mass produced DRGH antennas are reduced or eliminated. It was hypothesised that gaps most notable in the waveguide launcher section and especially the coaxial feeding section is the cause of the sharp resonance effects. This hypothesis was confirmed during the study. A highly accurate Method of Moments (MoM) numerical model of the 1-18 GHz DRGH antenna was developed, gaps were then implemented in between various parts of the model and the results observed. Based on these results a new improved 1-18 GHz DRGH antenna was designed with reduced sensitivity to manufacturing tolerances and improved performance. / Dit is alombekend dat die 1-18 GHz Dubbel Rif Golfleier Horing (DRGH) antenna baie sensitief is vir vervaardigings toleransies. 'n Tipiese DRGH antenna bestaan uit verskeie individuele onderdele. Toleransies in vervaardiging, selfs al word die proses numeries beheer, kan dus lei tot spasies tussen verskillende dele. Die waarneming van verswakte werkverrigting, meer spesifiek resonansies in die wins en Spannings Staande Golf Verhouding (SSGV) by 'n aantal vervaardigde 1-18 GHz DRGH antennes het gelei tot verdere studie. Om die 1-18 GHz ontwerp minder sensitief te maak ten opsigte van toleransies, moes die presiese oorsaak van die verswakte werkverrigting bepaal word. Aan die begin van die studie was die vermoede dat spasies in veral die golfleierlanseerder en meer spesifiek die koaksiale voer seksie, die oorsaak is van die resonansies. Die hipotese is in die daaropvolgende ondersoek bevestig. 'n Hoogs akkurate Metode van Momente (MvM) numeriese model is vir die 1-18 GHz DRGH antenna ontwikkel. Spasies is tussen verskeie parte van die model ge-inkorporeer en die resultate is ondersoek. 'n Nuwe verbeterde 1-18 GHz DRGH antenna op die ondersoek gebaseer, is ontwikkel. Die antenna het verminderde sensitiwiteit ten opsigte van vervaardigings toleransies sowel as verbeterde werkverrigting. / Dissertation (MEng)--University of Pretoria, 2011. / Electrical, Electronic and Computer Engineering / Unrestricted

No description available.

Thesis (PhD)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: This dissertation presents modal-based techniques for the effective systematic design of quadruple-ridged flared horns (QRFHs) as reflector feeds for radio astronomy applications. A new excitation technique is proposed, consisting of a quadraxial line that terminates in the quad-ridges through the back lid of the QRFH, which allows for the integration with differential low-noise amplifiers. An equivalent circuit of this quadraxial feed is presented that allows fast synthesis of optimal feeding designs for QRFHs. In addition, the quadraxial feeding network suppresses higher-order modes significantly. The effect of eliminating these unwanted modes are investigated and the quadraxial feed is shown to outperform the coaxial feed in the known detrimental aspects of the QRFH – beamwidth narrowing for increased frequency, beamwidth variation over the upper bandwidth, high cross-polarisation levels, high co-polar sidelobes and variable phase centre – for the specific QRFH designs. Ridge-loaded modes are analysed and a large number of cut-off frequencies presented which are unavailable in literature. The pure-mode excitation of the quadraxial feed allows more effective control over the modal content in the QRFH. This is exploited in a proposed design technique where the cut-off frequencies throughout the horn are used to synthesise the ridge taper profile, in order to achieve the desired modal distribution in the aperture. The proposed feeding solution is compact and therefore is also attractive for use with cryocoolers, typically employed with front-end electronics in telescopes for radio astronomy. A prototype was successfully manufactured and the mechanical implementation of the quadraxial feed proved to be much more simple than that of the conventional feed – consisting of a coaxial line realised within the thin ridges. / AFRIKAANSE OPSOMMING: Hierdie proefskrif stel modus gebasseerde tegnieke voor vir die effektiewe sistematiese ontwerp van viervoud gerifte oopgesperde horings (VGOHs) as weerkaatser voere vir radio astronomie toepassings. ’n Nuwe voertegniek word voorgestel, wat bestaan uit ’n kwadraksiale lyn wat termineer in die vier riwwe deur die agterkant van die VGOH, wat die integrasie met differensiële laeruis versterkers toelaat. ’n Ekwivalente stroombaan van hierdie kwadraksiale voer word aangebied vir die vinnige sintese van optimale voer ontwerpe vir VGOHs. Boonop onderdruk die kwadraksiale voer netwerk ook beduidend hoër orde modusse. Die effek van die uitskakeling van hierdie ongewensde modusse word ondersoek en die kwadraksiale voer oortref die gedrag van die koaksiale voer in die bekende nadelige aspekte van die VGOH – bundelwydte vernouing met toenemende frekwensie, bundelwydte variasie oor die boonste bandwydte, hoë kruispolarisasie vlakke, hoë kopolarisasie sybande en wisselvallige fase senter – vir die spesifieke VGOH ontwerpe. Rifgelaaide modusse word geanaliseer en ‘n groot aantal afsnyfrekwensies word aangebied wat nie beskikbaar is in literatuur nie. Die suiwermodus opwekking van die kwadraksiale voer bied meer effektiewe beheer oor die modusinhoud in die VGOH. Hierdie aspek word benut in ‘n voorgestelde tegniek waar die afsnyfrekwensies deur die horing gebruik word om die rif tapsheid profiel te sintetiseer, sodat die gewensde modale distribusie in die stralingsvlak behaal word. Die voorgestelde voer oplossing is kompak en daarom ook aantreklik vir die gebruik met krioverkoelers, wat tipies gebruik word met die voorkant elektronika in teleskope vir radio astronomie. ‘n Prototipe was suksesvol vervaardig en die meganiese implimentasie van die kwadraksiale voer toon dat dit eenvoudiger is as met die gebruiklike koaksiale voer – wat bestaan uit ‘n koaksiale lyn bewerkstellig binne die dun riwwe.

It is well known that quad-ridged horn antennas in general have impedance and radiation characteristics that are significantly worse than that of their double-ridged counterparts. Normally a voltage standing wave ratio (VSWR) of 3 over the operational bandwidth is used for the design specification of quad-ridged horn antennas. The bandwidth of operation is severely restricted due to the excitation of higher order modes in the co-axial to waveguide transition of the antenna. The higher order modes cause a break-up in the radiation pattern of the antenna and large dips in the boresight gain. The performance of the quad-ridged horn antenna with pyramidal sidewalls is improved by separating the antenna into the transition and flared horn sections, and optimizing these sections individually. It is shown that a transition section with a pyramidal cavity and steps, and a flared horn section with an exponential profile with a circular segment for the ridges deliver the best performance. These configurations for the transition and flared horn sections are combined in the complete antenna. The optimized antenna has a 12.5:1 operational bandwidth with improved performance in terms of the VSWR, the coupling between the ports and the boresight gain. A prototype of this antenna is manufactured. Good agreement between the measured and simulated performance is achieved. / Dissertation (MEng)--University of Pretoria, 2013. / gm2014 / Electrical, Electronic and Computer Engineering / unrestricted

A transmission line format is presented which takes the form of a Multilayer Ridged Substrate Integrated Waveguide, for which signal energy is transmitted within standard PCB substrates, within a wave-guiding structure formed from conducting tracks in the horizontal plane and arrays of through-plated vias in the vertical plane. The Substrate Integrated Waveguide (SIW) is a recent development into which research is so far concentrated on single-layer rectangular variants which, like traditional rectangular waveguide, are amenable to analytic computation of the cutoff eigenvalues. Recent publications have offered empirically-derived relationships with which a Substrate Integrated Waveguide can be analysed by equivalence of the horizontal dimensions with a conventional waveguide, allowing such structures to be designed with minimal effort. We propose a ridged form of this structure, in which multiple PCB layers are stacked to obtain the desired height and the published equivalent width is used to obtain the horizontal dimensions. The proposed structure combines the increased bandwidth of ridged waveguide with SIW’s greatly reduced cost of manufacture and integration, relative to conventional waveguide, and improved power handling capacity and loss susceptibility relative to microstrip. Ridged variants have not yet been studied in the literature, however, in part because the eigenspectrum can not be obtained analytically. We thus present a semi-analytical software model with which to synthesise and analyse the cutoff spectrum in ridged Substrate Integrated Waveguide, verified by comparison with analytical solutions, where they exist, simulation in finite-element software and a physical prototype. Agreement with simulated and measured results is within 1 % in certain subsets of the parameter space and 11 % generally, and individual results are returned in times of the order of seconds. We use the model to analyse the relationship between geometry and frequency response, constructing an approximating function for the early modes which is significantly faster, such that think it can be used for first-pass optimisation. A range of optimal parameters are presented which maximise bandwidth within anticipated planar geometric constraints, and typical design scenarios are explored.

Pagrindinis darbo tikslas – sukurti plačiajuostį rezistorinį jutiklį, skirtą didelės galios mikrobangų impulsams matuoti, kurio jautrusis elementas pagamintas iš n-tipo Si yra įmontuotas H tipo bangolaidyje. Rezistorinis jutiklis turėtų pasižymėti plokščia jautrio dažnine charakteristika, jo varža neviršyti 1 k, o stovinčios bangos koeficientas būti mažesnis nei 1,5. Disertacijoje yra pateikiami teoriniai elektrinio lauko pasiskirstymo bangolaidinėje sekcijoje su rezistorinio jutiklio jautriuoju elementu viduje modeliavimo baigtinių skirtumų laiko skalėje metodu rezultatai, kai jautrusis elementas yra talpinamas standartiniuose H tipo bangolaidžiuose WRD250 ir WRD840. Modeliavimo metu buvo ieškoma tokių jautriojo elemento matmenų ir savitosios varžos, kad rezistorinis jutiklis tenkintų aukščiau paminėtus reikalavimus. Disertacijoje taip pat aprašomi trijų skirtingų rezistorinių jutiklių, kurių optimalūs matmenys buvo surasti iš modeliavimo rezultatų, eksperimentiniai tyrimai. Buvo nustatytos šių jutiklių jautrio dažninės charakteristikos, jutiklių atsako signalo priklausomybė nuo mikrobangų galios ir stovinčios bangos koeficientas. Sujungus sukurtąjį jutiklį su plačiajuoste ruporine antena buvo atlikti mikrobangų galios tankio (elektrinio lauko stiprio) matavimai atviroje erdvėje. Pateikti disertacijoje internetinių maršrutizatorių ir šviesolaidinių konverterių elektromagnetinio atsparumo tyrimai, kuriuose rezistoriniai jutikliai naudojami elektrinio lauko stipriui... [toliau žr. visą tekstą] / The main goal of the thesis was the development of a resistive sensor, a sensing element of which made from n-type Si is mounted in a double ridge waveguide. Developed sensor was devoted for the measurement of high power microwave pulses. The sensor should meet the following requirements: its resistance should be lower than 1 k, a voltage standing wave ratio has been set < 1.5, and the frequency response of the sensor should be as flat as possible. In the thesis the results of theoretical calculation of electromagnetic fields inside waveguide segment with the sensing element of the resistive sensor mounted in the standard double ridged waveguides WRD250 and WRD840 are presented. Calculations have been performed using finite-difference time-domain method. The dimensions and specific resistance of the sensing element from the modeling results were chosen for the sensor that meets the requirements mentioned above. Corresponding sensors have been manufactured and their characteristics have been investigated experimentally. The sensitivity dependence on frequency, output signal dependence on microwave pulse power and voltage standing wave ratio were determined. Connecting the sensor to a wide band horn antenna the microwave pulse power density (electric field strength) in free space was measured. Resistive sensors were used for electric field strength measurement in the immunity against microwave radiation tests on internet routers and media converters demonstrating possible... [to full text]

The main goal of the thesis was the development of a resistive sensor, a sensing element of which made from n-type Si is mounted in a double ridge waveguide. Developed sensor was devoted for the measurement of high power microwave pulses. The sensor should meet the following requirements: its resistance should be lower than 1 k, a voltage standing wave ratio has been set < 1.5, and the frequency response of the sensor should be as flat as possible. In the thesis the results of theoretical calculation of electromagnetic fields inside waveguide segment with the sensing element of the resistive sensor mounted in the standard double ridged waveguides WRD250 and WRD840 are presented. Calculations have been performed using finite-difference time-domain method. The dimensions and specific resistance of the sensing element from the modeling results were chosen for the sensor that meets the requirements mentioned above. Corresponding sensors have been manufactured and their characteristics have been investigated experimentally. The sensitivity dependence on frequency, output signal dependence on microwave pulse power and voltage standing wave ratio were determined. Connecting the sensor to a wide band horn antenna the microwave pulse power density (electric field strength) in free space was measured. Resistive sensors were used for electric field strength measurement in the immunity against microwave radiation tests on internet routers and media converters demonstrating possible... [to full text] / Pagrindinis darbo tikslas – sukurti plačiajuostį rezistorinį jutiklį, skirtą didelės galios mikrobangų impulsams matuoti, kurio jautrusis elementas pagamintas iš n-tipo Si yra įmontuotas H tipo bangolaidyje. Rezistorinis jutiklis turėtų pasižymėti plokščia jautrio dažnine charakteristika, jo varža neviršyti 1 k, o stovinčios bangos koeficientas būti mažesnis nei 1,5. Disertacijoje yra pateikiami teoriniai elektrinio lauko pasiskirstymo bangolaidinėje sekcijoje su rezistorinio jutiklio jautriuoju elementu viduje modeliavimo baigtinių skirtumų laiko skalėje metodu rezultatai, kai jautrusis elementas yra talpinamas standartiniuose H tipo bangolaidžiuose WRD250 ir WRD840. Modeliavimo metu buvo ieškoma tokių jautriojo elemento matmenų ir savitosios varžos, kad rezistorinis jutiklis tenkintų aukščiau paminėtus reikalavimus. Disertacijoje taip pat aprašomi trijų skirtingų rezistorinių jutiklių, kurių optimalūs matmenys buvo surasti iš modeliavimo rezultatų, eksperimentiniai tyrimai. Buvo nustatytos šių jutiklių jautrio dažninės charakteristikos, jutiklių atsako signalo priklausomybė nuo mikrobangų galios ir stovinčios bangos koeficientas. Sujungus sukurtąjį jutiklį su plačiajuoste ruporine antena buvo atlikti mikrobangų galios tankio (elektrinio lauko stiprio) matavimai atviroje erdvėje. Pateikti disertacijoje internetinių maršrutizatorių ir šviesolaidinių konverterių elektromagnetinio atsparumo tyrimai, kuriuose rezistoriniai jutikliai naudojami elektrinio lauko stipriui... [toliau žr. visą tekstą]

The thesis deals with broadband antennas for measurement purposes. A ridged horn antenna has been selected for this concept, designed for the frequency range 0.9 GHz to 9 GHz. This work contains general theoretical description of antennas and further it focuses on a specific design of the ridged horn antenna, beginning with the calculation of its dimensions, modeling and optimization to obtain desired antenna properties. Finally, the antenna was constructed and measured. The reflection factor s11