Thesis (PhD)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: The triple layer pillbox antenna is an antenna topology well suited for use as a stackable "plank" element in radar applications. Its suitability arises from the folding which makes it compact, and from the layered nature which can be exploited for low cost manufacture. Existing designs of these "cheese" antennas, whether two or three layers, suff er from two drawbacks: a) The bend or fold between layers introduces undesirable reflections and b) Due to their parabolic sector geometry virtually no pattern control is available to the designer. This work addresses both of these shortcomings. A low reflection transition is realized by introducing simple compensating elements into the design which, with minimal manufacturing complexity, off er high performance over a broad frequency and incidence angle range. To cater for pattern control the concept of "dual shaped reflectors" is borrowed from the high performance dish antenna literature and implemented in the pillbox geometry. This shaping off ers limited but useful control of the aperture distribution and thus indirectly over the radiation pattern. To test these innovations three X-band antennas have been designed, built and measured. An initial unshaped geometry is used for the fi rst design to show the fold or bend performance. This antenna has a simulated and measured 2GHz usable bandwidth, with a reflection coeffi cient below -10dB and side-lobes below -27dB over a bandwidth in excess of 20%. Shaping is then added to show how either side-lobe levels can be lowered to below -32dB, or the gain enhanced by 2dB. The enhanced designs have been built and experimentally veri fied. / AFRIKAANSE OPSOMMING: Die drie-dubbel gevoude pildoos antenna is `n antenna topologie wat goed gepas is vir die gebruik as `n stapelbare "plank" element vir radar aanwending. Sy geskiktheid kom vanwee die vou van die struktuur wat dit meer kompak maak sowel as die konstruksie moontlik goedkoper maak. Huidige ontwerpe van die antenna strukture, hetsy twee of drie lae, ly aan twee tekortkominge: a) Die buiging of vou tussen die lae veroorsaak ongewensde weerkaatsings en b) Weens hul paraboliese meetkunde is feitlik geen beheer oor die stralings patroon beskikbaar nie. Hierdie werk spreek beide hierdie tekortkominge aan. `n Lae weerkaatsing by die oorgang is verkry deur eenvoudige kompenserende elemente by die ontwerp in te voeg wat, met minimale vervaardigings kompleksiteit, hoë werkverrigting lewer oor `n breë frekwensie en invals hoek spektrum. Om patroon beheer te voorsien is die konsep van "dubbele gevormende weerkaatsers" geleen vanaf die hoë verkverrigting skottel antenna literatuur en in die pildoos meetkunde ingestel. Hierdie vorming lewer beperkte dog nuttige beheer oor die openings verspreiding en dus indirek oor die stralings patroon. Om hierdie nuwighede te toets is drie X-band antennas ontwerp wat gebou en gemeet is. 'n Aanvanklike ongevormende meetkunde is gebruik vir die eerste ontwerp om die vou of buiging se werksverrigting te bewys. Hierdie antenna het `n gesimuleerde en gemete 2GHz bruikbare bandwydte met `n weerkaatsings kwosiënt onder -10dB en sylobbe van minder as -27dB oor `n bandwydte van meer as 20%. Vorming is dan bygevoeg om te bewys dat of verlaagde sylobbe van onder -32dB of verhoogde aanwins met 2dB verkrygbaar is. Die verbeterde ontwerpe is gebou en eksperimenteel bewys.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2007. / This thesis examines three reduced complexity algorithms for subspace tracking in the context of radio direction finding. Projection Approximation Subspace Tracking (Yang), the Fast Data Projection Method (Doukopoulos and Moustakides) and OPERA (MacInnes) are presented and compared in terms of performance and efficiency. The algorithms’ performances are contrasted using step changes in direction of arrival, sensitivity to noise and minimum angular discrimination. Their relative efficiencies are examined by comparing their theoretical complexities and by assessing benchmark results. The construction of a PC based signal simulator and direction finding client using the MUSIC algorithm are described. The results of a field assessment of the algorithms are presented, and finally, conclusions regarding the relative merits of the algorithms are drawn.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2008. / An existing antenna used in satellite communications is investigated with the goal of improving low angle radiation performance and reducing manufacturing costs. To understand this antenna it is modelled, simulated and verified against existing measurements. This verified model is the basis for further investigation. The antenna is separated into two parts with are individually examined and enhancements are proposed for each. Simulations of the resulting final models show that little by way of improvement in the performance can be obtained but bring several key issues to light. The scanning impedance is of particular importance in such an investigation and a method of determining this impedance is recommended.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2006. / This thesis investigates a computational model of an electronically steered antenna array. It focuses on a simple element comprising an S-shaped, crossed, cylindrical cavity-backed slot antenna. An unusual aspect of the element is the addition of a top hat, which contributes to the low scanning ability of the array. The objective was to confirm this contribution of the top hat. During the investigation, the computation code Feko was validated for slot analysis through consideration of the basic properties of a dipole and slot and how they related to each other. Various alternative models were evaluated, before a final accurate model was modelled in Feko, to find possible equivalent models. The final model, which implemented the use of Feko as release 5, was the only one that achieved successful results. The results showed that the top hat does play an important role in the steering of the beam. The mechanism through which this occurs was identified. The results that where obtained indicated that there may be more effective elements than the cylindrical element and the identification of this is proposed as a field for further study.

A thesis submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg, 2017 / The scientific requirements for Radio Frequency (RF) receivers especially for Radio Astronomy have become more demanding, requiring: compact, low-profile, multi and wideband antennas and more sensitive receivers. Integration of the antenna into the receiver system is often critical to meet these demands. Noise theory to model these more complex systems is well developed but is not implemented in commercial solvers, given the niche market of the receivers it is only available using specialised software. If the system is closely coupled, it becomes necessary for design to incorporate Electromagnetic (EM) and Microwave (MW) modelling into the multi port noise modelling. CAESAR, a combined noise and EM/MW modelling code is available, but to use it requires the exclusive use of the CAESAR software, which is impractical given the utility and wide use of commercial solvers. Mathematical methods are developed to incorporate commercial solvers into the more specialised CAESAR, validated using a folded dipole and applied to a wideband Eleven antenna system, a compact form of a log periodic dipole array. The Eleven antenna consist of eight single ended or four differential ports, with a closely coupled feeding arrangement. Cryogenic measurements are done to verify the modelling, the measured sensitivity matches with the model closely in amplitude and shape, giving confidence to the approach, and allowing modelling but not system optimisation. Optimising the antenna based on receiver design and still being able to use commercial code requires the external scripting of a commercial solver. The EDITFEKO (card based) module of FEKO (a powerful and versatile solver) is used along with the meshing software GMSH and GNU Octave. Optimisation of system sensitivity is demonstrated on a choke horn fed reflector system at 1420MHz. This optimisation method is applied to a practical application, an octave band system (4:5 GHz to 9 GHz) for the Hartebeesthoek Radio Observatory. The design is split into smaller simulations using waveguide modes and the associated S–parameters, the techniques are presented and checked on a truncated system. Initial design and optimisation are given. The combining of specialised multiport noise modelling design and optimisation within commercial EM/MW solvers allows more sensitive and specialised receivers to be built. Index terms— noise modelling, wideband, multiport, corrugated horn, octave band receiver, EM/MW optimisation / MT2018

Demand for wireless network capacity keeps growing exponentially every year, as a result a 1000-fold increase in data traffic is projected over the next 10 years in the context of 5G wireless networks. Solutions for delivering the 1000-fold increase in capacity fall into three main categories: deploying smaller cells, allocating more spectrum and improving spectral efficiency of wireless systems. Smaller cells at RF frequencies (1-6GHz) are unlikely to deliver the demanded capacity increase. On the other hand, millimeter-wave spectrum (frequencies over 24GHz) offers wider, multi-GHz channel bandwidths, and therefore has gained significant research interest as one of the most promising solutions to address the data traffic demands of 5G. Another disruptive technology is full-duplex which breaks a century-old assumption in wireless communication, by simultaneous transmission and reception on the same frequency channel. In doing so, full-duplex offers many benefits for wireless networks, including an immediate spectral efficiency improvement in the physical layer. Although FD promises great benefits, self-interference from the transmitter to its own receiver poses a fundamental challenge. The self-interference can be more than a billion times stronger than the desired signal and must be suppressed below the receiver noise floor. In recent years, there has been some research efforts on fully-integrated full-duplex RF transceivers, but mm-wave fully-integrated full-duplex systems, are still in their infancy. This dissertation presents novel architectures, antenna and circuit techniques to merge two exciting technologies, mm-wave and full-duplex, which can potentially offer the dual benefits of wide bandwidths and improved spectral efficiency. To this end, two different antenna interfaces, namely a wideband reconfigurable T/R antenna pair with polarization-based antenna cancellation and an mm-wave fully-integrated magnetic-free non-reciprocal circulator, are presented. The polarization-based antenna cancellation is employed in conjunction with the RF and digital cancellation to design a 60GHz full-duplex 45nm SOI CMOS transceiver with nearly 80dB self-interference suppression. The concepts and prototypes presented in this dissertation have also profound implications for emerging applications such as vehicular radars, 5G small-cell base-stations and virtual reality.

Grid-scale integration of renewable energy sources and smart grid devices has created new demands in flexible power conversion. State-of-the-art semiconductor power switches present limitations in power handling capability, as well as forward and reverse breakdown voltages. Superconducting materials are a viable alternative due to their robustness against high ampacities, large electric fields and abrupt changes in power flow. This work pays focus to material testing and apparatus design for an antenna-coupled cryotron (ACC), which is a superconducting power switch.Design, fabrication and testing are examined for a longitudinal resonant cavity, paired with monopole transmit and modified slot receive antennae. These couple radio frequency (RF) energy into superconducting thin film niobium (Nb) carrying high current densities (∼105A/cm2), thereby creating an antenna-coupled cryotron.Induced electromagnetic field effects at the receive antenna alter superconductive fluid dynamics. The theorized quality in manipulating this mechanism is a rapid normal-conductivity transition (µs), which affects a switch "off" state. Functional evaluation of the device as a waveguide revealed evanescent mode resonance at frequencies below the waveguide cut-off of ∼18GHz. The thin film Nb was deposited on a quartz dielectric, which penetrated the waveguide and supported evanescent resonances within the structure.Altered resistivity and critical transition-point properties emerged from device testing at applied RF. When the Nb film temperature-dependent coherence length was comparable to its thickness, perpendicular magnetic field application generated an Abrikosov vortex state, energetically favoring a mixed domain condensate. Interaction of the magnetically-induced flux vortex lattice with Lorentz current forces gave rise to resistive changes within the metal. Three resistive transition mechanisms developed: a latch to normal state resistance, attributed to cooper-pair destruction avalanche induced near critical transition points; a small reversible increase in resistance (∼mV), arising from flux-flow within an intermediate state at peak resonance; as well as temporal alterations in superfluid dynamics from disequilibrium in the quasi-particle population. The RF induced superfluid effects were observable in separate terms of electric and thermodynamic fluctuations.Motivation for this work is the eventual design of a high voltage, high current and low cost power switch, able to function where existing semiconductor technology fails. Concentration is paid to the fundamental theory, physics and methodology in conceptual testing and design of prototype ACCs. Assessment focuses on preliminary findings and concludes with next stage design requirements.

No description available.

Also issued as a Ph.D. thesis in the Dept. of Electrical Engineering, 1968. / Bibliography: p.91-93.

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 161-164).