3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Analysis and design of simple antenna geometries for broadband high frequency communications.(1991) Fourie, Andries Petrus Cronje.The general argument of the thesis is that the design of broadband antennas demands a thorough understanding of the factors influencing the current distribution on antenna wires. Specifically. current distribution concepts are used to improve the evaluation and design of small broadband antennas for the high frequency (HF) 2 to 30 MHz range. The current distribution on an antenna governs its input impedance, radiation efficiency and radiation patterns. (Abbreviation abstract)Item Integration of noise modelling into RF receiver design(2017) Klein, BenjaminThe 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 optimisationItem Channel modelling and analysis of Wits mock-mine with different antenna parameters(2017) Hussain, IntikhabIn the mining industry, communications systems are important for ensuring personnel safety and optimizing the mining processes underground. Achieving robust and reliable through-the-air (TTA) communication systems has always been a challenge in the underground mining environment due to harsh and dynamic conditions. TTA requires radio channel characterization for efficient designing and deploying of the communications systems. The literature covers the statistical radio propagation of a room and pillar coal mine, a longwall coal mine, CANMET Gold mine, Camborne School of Mines hard rock mine tunnel, MUZ Coal mine, an iron-ore mine and a lead-zinc mine with linearly polarized antennas at different frequencies. [Abbreviated Abstract. Open document to view full version]Item Development of self and mutual impedance theory to analyse arrays comprising half wave dipole and folded dipole elements.(1993) Clark, Alan, RobertThe aim of the thesis is to develop techniques for the analysis of antennas composed of dipoles and folded dipoles,that are efficient relative to the method-of-moments. (Abbreviation abstract)Item Simple meteor scatter out-station antennas(2015-02-05) Givati, OferT his dissertation examines simple Meteor Burst Communication (M B C) out-starioL * i-^nas. The eSect o f illum ination gain, beam w idth and orientation was studied using computer ^vr.t-iation. Sim ilarly, the performance o f M B C links using a half-wave dipole, a quarter-wave rnonopole, a square loop, a long w ue and a 5-elements Yagi-Uda antennas was determined. The performance o f these links are related to the antennas’ sky i l l umination. This investigation provides designers some bench-mark results which indicate the role played by the antennas ’ radiation patterns in M B C. A value system was formulated to provide practical and electrical trade-offs fo r m obile andmanpack antennas in the meteor scatter environment. Simulated results indicate that simple antennas cause degraded communications due to their reduced size and complexity. The conclusion is that the directional master station should provide adequate sky illumination. I t is recommended that the results obtained be validated by measurements and further work concentrate on master station antennas.