Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The extension of the Karoo Array Telescope (KAT), MeerKAT, will be the most sensitive radio telescope in the southern hemisphere until it is superseded by the completion of the Square Kilometre Array (SKA). These instruments are to be constructed in the Karoo which is an area in South-Africa that is protected against Radio Frequency Interference (RFI) by the Astronomy Geographical Advantage (AGA) act. However, the telescope is also vulnerable to self-generated interference and specialised measurement systems are required to monitor RFI levels. The development of a ReAl Time Transient AnalYser (RATTY) is described and two Experimental Development Models (XDM) are compared. The first uses a mixing philosophy, and the second direct-sampling. The selection of these models was based on the evaluation of several analogue Front-End (FE) designs. A stripline-filter design process is presented along with the results obtained for custom filters developed for the FEs. Several analyses were compared to measurements performed with one of the devices and good agreement was shown between the system characteristics. Issues regarding the Spurious Free Dynamic Range (SFDR) of the FE designs were identified in the process and measurement-corrected simulations used to predict the achievable ranges. The outcome of the XDM comparison promotes the continued development of a direct-sampling strategy to fulfil the short-term goals of the project. A static calibration procedure is demonstrated for the mixing system and implemented to account for different FE configurations. An overview of the digital and software components of the RATTY system is given and Electromagnetic Compatibility (EMC) principles are applied during the construction of both systems. / AFRIKAANSE OPSOMMING: Die finale fase van die Karoo Reeks Teleskoop (KAT), MeerKAT, sal die sensitiefste radio teleskoop in die suidelike halfrond wees. Dit sal egter oortref word deur die vierkante kilometer reeks, wat die sensitiefste radio teleskoop ter wêreld sal word. Beide instrumente sal vatbaar wees vir radiofrekwensie steurings en sal opgerig word in ‘n wet-beskermde omgewing. Die teleskope is ook vatbaar vir radiofrekwensie steurings wat deur interne stelsels opgewek kan word. Dus word gespesialiseerde meetapparate benodig om die betrokke area en substelsels van die teleskope te monitor. Die ontwikkeling van ‘n meetinstrument vir die ontleding van kort-durasie tydseine (RATTY) word beskryf en twee eksperimentele ontwikkelings modelle word vergelyk. Hierdie modelle is gebaseer op die verfyning van voorafgaande ontwerpe vir die analoog substelsel van die instrument en hierdie proses word verduidelik. Die eerste model volg ‘n menger strategie waar die tweede model direkte-monstering implementeer. ‘n Dubbel-laag, mikrostrookfilter ontwerpsproses word beskryf en die gemete resultate vir die ontwikkelde filters word bespreek. Verskeie ontledings is aangewend en vergelyk met die gemete resultate van die stelsels. Hieruit word bevredigende ooreenkomste getref. Die beperkings van die modelle, weens interne distorsie, word geïdentifiseer in dié proses en verdere skattings word gemaak d.m.v. simulasies. Die eksperimentele modelle word vergelyk en die voorkeur van ‘n direkte-monsterings stelsel word gemotiveer. Die digitale en sagteware komponente word oorsigtelik behandel. Tydens die konstruksie van die modelle word die toepassing van elektromagnetiese verenigbaarheids beginsels verduidelik. Laastens word ‘n eenvoudige kalibrasie toegepas op die menger stelsel en ‘n toepassing daarvan word behandel.

The largest 21st century radio telescope, the Square Kilometre Array (SKA) is now being planned, and the first phase of construction is estimated to commence in the year 2016. Phased array technology, the key feature of the SKA, requires the use of a tremendous number of receivers, estimated at approximately 37 million. Therefore, in the context of this project, the Low Noise Amplifier (LNA) located at the front end of the receiver chain remains the critical block. The demanding specifications in terms of bandwidth, low power consumption, low cost and low noise characteristics make the LNA topologies and their design methodologies one of the most challenging tasks for the realisation of the SKA. The LNA design is a compromise between the topology selection, wideband matching for a low noise figure, low power consumption and linearity. Considering these critical issues, this thesis describes the procedure for designing a monolithic microwave integrated circuit (MMIC) LNA for operation in the mid frequency band (400 MHz to 1.4 GHz) of the SKA. The main focus of this work is to investigate the potential of MMIC LNA designs based on a novel InGaAs/InAlAs/InP pHEMT developed for 1 µm gate length transistors, fabricated at The University of Manchester. An accurate technique for the extraction of empirical linear and nonlinear models for the fabricated active devices has been developed. In addition to the linear and nonlinear model of the transistors, precise models for passive devices have also been obtained and incorporated in the design of the amplifiers. The models show excellent agreement between measured and modelled DC and RF data. These models have been used in designing single, double and differential stage MMIC LNAs. The LNAs were designed for a 50 Ω input and output impedance. The excellent fits between the measured and modelled S-parameters for single and double stage single-ended LNAs reflects the accurate models that have been developed. The single stage LNA achieved a gain ranging from 9 to 13 dB over the band of operation. The gain was increased between 27 dB and 36 dB for the double stage and differential LNA designs. The measured noise figures obtained were higher by ~0.3 to ~0.8 dB when compared to the simulated figures. This is due to several factors which are discussed in this thesis. The single stage design consumes only a third of the power (47 mW) of that required for the double stage design, when driven from a 3 V supply. All designs were unconditionally stable. The chip sizes of the fabricated MMIC LNAs were 1.5 x 1.5 mm2 and 1.6 x 2.5 mm2 for the single and double stage designs respectively. Significantly, a series of differential input to single-ended output LNAs became of interest for use in the Square Kilometre Array (SKA), as it utilises differential output antennas in some of its configurations. The single-ended output is preferable for interfacing to the subsequent stages in the analogue chain. A noise figure of less than 0.9 dB with a power consumption of 180 mW is expected for these designs.

Thesis (PhD (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: South Africa and Australia are now the two remaining countries bidding for the Square Kilometre Array (SKA), the biggest and most sensitive project ever undertaken in radio astronomy. The South African SKA is demonstrating its technology capabilities through the Karoo Array Telescope (KAT or MeerKAT). The development of KAT is taking place in stages to optimise design and minimise risks at each stage. An array of seven 12 m antennas will be complete by the end of 2009, called KAT-7. The following phase will see the construction of MeerKAT, which will lead to eighty arrayed dishes. Lightning and RFI studies for KAT-7 are the focus of this dissertation. Due to the extent and complexity of the South African demonstrator project, these studies have largely been conducted on a single structure. Parameters for the dish antenna and pedestal design changed throughout their development. To be effective, the doctoral research had to track these changes appropriately. A Method of Moments frequency domain computational electromagnetic code, FEKO, is used throughout the study. The consequences of direct and indirect lightning strikes are examined for the KAT-7 structure. Important FEKO model verification is achieved through measurement of physical scale models in an anechoic chamber. The microwave simulation code, CST, gives direct comparison of FEKO results by using a finite volume time domain method of calculation. Using frequency domain analysis on these models, the lightning down conductor design over the dish antenna bearings is optimised with cost-effectiveness as one driving parameter. RFI coupling levels for different designs are compared to each other to identify areas requiring RFI mitigation. Analysis of resonances enables evaluation of the mitigation at frequencies sensitive to radio astronomy. A Sommerfeld integral ground plane is used together with the computational model to investigate the use of the concrete foundation steel reinforcing as part of the lightning earthing electrode system. Different interconnections of the steel reinforcing elements are critically evaluated. The KAT-7 design incorporated clear lightning protection and RFI mitigation policies derived from recommendations contained within this dissertation. / AFRIKAANSE OPSOMMING: Suid-Afrika en Australie is nou die oorblywende twee lande wat bie vir die Vierkante Kilometer Reeks (SKA), die grootste en mees sensitiewe projek nog ooit in radio astronomie onderneem. Die Suid Afrikaanse SKA demonstreer sy tegnologiese bekwaamheid met die Karoo Reeks Teleskoop (KAT of MeerKAT). Die ontwikkeling van KAT vind plaas in fases om die ontwerp te optimaliseer en risikos te minimaliseer met elke fase. ’n Reeks van sewe 12 m antennas, genaamd KAT-7, sal teen die einde van 2009 klaar wees. Die volgende fase behels die konstruksie van MeerKAT, wat sal lei tot ’n tagtig-skottel reeks. Die fokus van hierdie proefskrif hanteer weerlig en radiofrekwensie steurings (RFS) vir KAT-7. As gevolg van die omvang en kompleksiteit van die Suid-Afrikaanse demonstreerder projek, is die studies hoofsaaklik op een struktuur gedoen. Parameters vir die antenna-skottel en -voetstuk ontwerp het met hul ontwikkeling deurgaans verander. Om effektief te wees, moes die doktorale navorsing hierdie veranderinge toepaslik volg. ’n Metode-van-Momente frekwensiedomein rekenaar elektromagnetiese kode, FEKO, is deurgaans met die studie gebruik. Die gevolge van direkte en indirekte weerligslae vir die KAT-7 struktuur is ondersoek. Belangrike FEKO model bevestiging is bereik met metings van skaalmodelle in ’n anego¨ıse kamer. Die mikrogolf-simulasie kode, CST, gee ’n direkte vergelyking met die FEKO resultate deur ’n eindige-volume-tyd-domein metode van berekening te gebruik. Met behulp van frekwensiedomein analise van hierdie modelle, is die weerligafleierontwerp oor die antenna-skottel laers ge-optimaliseer, met koste-effektiwiteit as een van die drywingsparameters. RFS koppelingsvlakke vir onderskeie ontwerpe is teen mekaar opgeweeg om areas te identifiseer wat RFS tempering benodig. Analise van resonansies stel die evaluering van die tempering in staat teen frekwensies wat sensitief is vir radio astronomie. ’n Sommerfeld integrale grondvlak word saam met die rekenaarmodel gebruik om die insluiting van die beton se staalversterking as deel van die aardingselektrodestelsel te ondersoek. Verskillende bindmetodes van die onderlinge staalversterkingselemente word krities ge¨evalueer. Die KAT-7 ontwerp inkorporeer duidelike weerligbeveiligings- en RFS temperingstrategie ¨e, komende van aanbevelings in hierdie proefskrif omskryf

The Square Kilometre Array (SKA) is a multibillion and a multinational science project to build the world’s largest and most sensitive radio telescope. For a very large field of view, the combined collecting area would be one square kilometre (or 1, 000, 000 square metre) and spread over more than 3,000 km wide which will require a massive count of antennas (thousands). Each of the antennas contains hundreds of low noise amplifier (LNA) circuits. The antenna arrays are divided into low, medium and high operational frequencies and located at different positions to boost up the telescope’s scanning sensitivity.The objective of this work was to develop and fabricate fully on-chip LNA circuits to meet the stringent requirements for the mid-frequency array from 0.4 GHz to 1.4 GHz of the SKA radio astronomy telescope using Monolithic Microwave Integrated Circuit technology (MMIC). Due to the number of LNA reaching figures of millions, the fabricated circuits were designed with the consideration for low cost fabrication and high reliability in the receiver chain. Therefore, a relaxed optical lithography with Lg = 1 µm was adopted for a high yield fabrication process.Towards the fulfilment of the device’s low noise characteristics, a large number of device designs, fabrication and characterisation of InGaAs/InAlAs/InP pHEMTs were undertaken. These include optimisations at each critical fabrication steps. The device’s high breakdown and very low gate leakage characteristics were further improved by a combination of judicious epitaxial growth and manipulation of materials’ energy gaps. An attempt to increase the device breakdown voltage was also employed by incorporating Field Plate structure at the gate terminal. This yielded the devices with improvements in the breakdown voltage up to 15 V and very low gate leakage of 1 µA/mm, in addition to high transconductance (gm) characteristic. Fully integrated double stage LNA had measured NF varying from 1.2 dB to 1.6 dB from 0.4 GHz to 1.4 GHz, compared with a slightly lower NF obtained from simulation (0.8 dB to 1.1 dB) across the same frequency band.These are amongst the attractive device properties for the implementation of a fully on-chip MMIC LNA circuits demonstrated in this work. The lower circuit’s low noise characteristic has been demonstrated using large gate width geometry pHEMTs, where the system’s noise resistance (Rn) has successfully reduced to a few ohms. The work reported here should facilitate the successful implementation of rugged low noise amplifiers as required by SKA receivers.