Waveguide antenna feed for the Square Kilometre Array

Thesis (MscEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2011.ENGLISH ABSTRACT: The aim of this thesis is to investigate the suitability of TEM (Transverse Electromagnetic) horn antennas for use as feed structures for the Square Kilometre Array (SKA) radio telescope, in particular with regard to the roundness of the radiation pattern. A literature study shows that existing TEM horn designs do not yield a round radiation pattern over a wide bandwidth and that an alternative is required. The Method of Moments (MoM) is a computational electromagnetic (CEM) technique typically used in the analysis of TEM horn antennas. An in-house MoM solver is successfully developed to analyse such antennas and is able to calculate the current density on the surface of a conductor, as well as the farfield patterns of an antenna. A modification to an exponential TEM horn antenna is proposed and simulations show the modification is successful in yielding a round radiation pattern over a wide bandwidth. The modified exponential TEM horn has a convex triangular arc at the end of each antenna plate and is constructed for measurement. Due to limited construction capabilities, the measurements deviate slightly from the simulated results but still indicate the potential of the structure to yield a round radiation pattern over a wide bandwidth.AFRIKAANSE OPSOMMING: Die doel van hierdie tesis is om die geskiktheid van transverse elektromagnetiese (TEM) horing antennas te ondersoek vir die gebruik as voerstrukture vir die Square Kilometre Array (SKA)- radioteleskoop, veral met betrekking tot die rondheid van die stralingspatroon. ’n Literatuurstudie toon dat bestaande TEM horing ontwerpe nie ’n ronde stralingspatroon oor ’n wye bandwydte lewer nie, en dat ’n alternatief nodig is. Die metode van momente is ’n rekenbare elektromagnetiese tegniek wat tipies gebruik word in die ontleding van TEM horing antennas. ’n In-huis metode van momente ontleder is suksesvol ontwikkel om sulke antennas te analiseer en is in staat om die stroomdigtheid op die oppervlak van ’n geleier, sowel as die vêrveld patrone van die antenna te bereken. ’n Wysiging van ’n eksponensiële TEM horing antenna word voorgestel en simulasies toon dat die veranderings suksesvol is om ’n ronde stralingspatroon oor ’n wye bandwydte te skep. Die verander eksponensiële TEM horing het ’n konvekse driehoekige boog aan die einde van elke antenna plaat en is gebou vir meting. Weens beperkte konstruksie vermoëns, toon die metings ’n afwyking van die gesimuleerde resultate, maar dui nogsteeds die potensiaal aan van die struktuur om ’n ronde stralingspatroon te lewer oor ’n wye bandwydte

Early detection of communication delays with the PEDS tools in at-risk South African infants

Background: Prevalence of communication delays or disorders is increasing, possibly because of various environmental risk factors. Selection and implementation of effective screening tools are important to detect at-risk infants as early as possible. This study aimed to evaluate the accuracy of the Parents' Evaluation of Developmental Status (PEDS), PEDS-Developmental Milestones and PEDS tools to detect communication delays in infants (6-12 months) in a South African primary healthcare context. Method: A comparative study design evaluated the accuracy of the PEDS tools to detect communication delays, using an internationally accepted diagnostic assessment tool, the Rossetti Infant-Toddler Language Scale (RITLS). A convenience sample of 201 infants was selected at primary healthcare clinics. Results: Expressive and receptive language sensitivity scores were low across all three screens (ranging between 14% and 44%). The PEDS tools had high sensitivity (71%) and specificity (73%) ratings for the receptive and expressive language and socio-emotional domain in combination. Conclusion: In the sample population, the PEDS tools did not accurately detect receptive and expressive language delays; however, communication delays in general were identified. Future research determining accuracy of the PEDS, PEDS-Developmental Milestones and PEDS tools for children aged 2-5 years in detecting communication delays should be prioritised

Early detection of communication delays with the PEDS tools in at-risk South African infants

BACKGROUND : Prevalence of communication delays or disorders is increasing, possibly because of various environmental risk factors. Selection and implementation of effective screening tools are important to detect at-risk infants as early as possible. This study aimed to evaluate the accuracy of the Parents’ Evaluation of Developmental Status (PEDS), PEDS-Developmental Milestones and PEDS tools to detect communication delays in infants (6–12 months) in a South African primary healthcare context. METHOD : A comparative study design evaluated the accuracy of the PEDS tools to detect communication delays, using an internationally accepted diagnostic assessment tool, the Rossetti Infant-Toddler Language Scale (RITLS). A convenience sample of 201 infants was selected at primary healthcare clinics. RESULTS : Expressive and receptive language sensitivity scores were low across all three screens (ranging between 14% and 44%). The PEDS tools had high sensitivity (71%) and specificity (73%) ratings for the receptive and expressive language and socio-emotional domain in combination. CONCLUSION : In the sample population, the PEDS tools did not accurately detect receptive and expressive language delays; however, communication delays in general were identified. Future research determining accuracy of the PEDS, PEDS-Developmental Milestones and PEDS tools for children aged 2–5 years in detecting communication delays should be prioritised.The Mellon Foundation for funding the vulnerable children programme of the Faculty of Humanities, University of Pretoria, the COPC Living Laboratory of the University of Pretoria and the National Research Foundation.http://www.ajod.orgam2016Speech-Language Pathology and Audiolog