Hybrid method of moments/uniform geometrical theory of diffraction techniques

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dc.contributor.advisorDavidson, D. B.en_ZA
dc.contributor.authorKeunecke, Svenen_ZA
dc.contributor.otherStellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.en_ZA
dc.date.accessioned2012-08-27T11:37:17Zen_ZA
dc.date.available2012-08-27T11:37:17Zen_ZA
dc.date.issued1998en_ZA
dc.descriptionThesis (M. Ing.) -- University of Stellenbosch, 1998.en_ZA
dc.description.abstractENGLISH ABSTRACT: This thesis investigates a hybrid method of moments/unified geometrical theory of diffraction formulation. In computational electromagnetics, numerical techniques are classified into two groups, namely the full wave solvers (sometimes also called low frequency techniques in the literature, due to the size of the problem being limited to only a number of wavelengths) and high frequency approximate techniques. The full wave solvers are accurate but require large amounts of computational resources when the problems in question are a number of square wavelengths in size. The high frequency techniques are in general accurate for problems that are very large in size compared to wavelength and become inaccurate as the problem becomes smaller. At present there is a "gap" between where the computational resources are exhausted and where the high frequency formulation becomes valid. In the future this gap will become smaller, but hybrid techniques will still be an "efficiency" consideration. A general method of moments formulation using overlapping sinusoidal basis and testing functions is presented. The formulation has been kept general so that structures like a monopole on a finite circular ground plane can be modelled by means of radial wires. For this purpose all the components of the electric field as a result of a current on a segment are required. In general only the derivation and explicit expressions for the z component of the electric field are available in the literature. The other component, the ρ component (using cylindrical coordinates, the Ø component is zero), had to be obtained by own initiative. The implementation of the method of moments formulation is then tested for a number of geometries to verify that certain aspects of the implementation of the formulation are correct. Results are given and are in good agreement with other method of moment implementations such as FEKO and NEC. The general theory and concepts behind the hybridisation process are then given. To illustrate the hybrid method of moments/uniform geometrical theory of diffraction, the author's general moment method code was modified to be able to solve a monopole on a finite circular ground plane. Further, to illustrate hybrid techniques using FEKO, the results of a simple problem of a dipole in front of a large plate have been shown. Here the advantage of either a hybrid method of moments/physical optics or a hybrid method of moments/uniform geometrical theory of diffraction are clearly shown. Following the simple example is a real world example, where an attempt was made to bridge the "gap" between the low frequency and the high frequency techniques.en_ZA
dc.description.abstractAFRIKAANSE OPSOMMING: Hierdie tesis ondersoek 'n hibriede moment metode/uniforme geometriese diffraksie formulering. Numeriese metodes in elektromagnetisme kan in twee afdelings geplaas word, naamlik die vollegolf oplossings (ook bekend in die literatuur as lae frekwensie tegnieke, omdat die grootte van die probleem tot 'n paar golflengtes beperk is) en die hoë frekwensie benaderde tegnieke. Die vollegolf tegnieke is akkuraat maar vereis groot hoeveelhede berekenings wanneer die probleme in beskouing groter is as ‘n paar vierkante golflengtes. Die hoë frekwensie tegnieke is oor die algeneem akkuraat vir probleme wat groot is m.b.t. die golflengte, en word al hoe minder akkuraat soos die problem Kleiner word. Op die oomblik bestaan daar ‘n “gaping” tussen waar die vollegolf oplossings te veel berekings vereis en waar die hoë frekwensie formulering toegepas kan word. In die toekoms sal hierdie “gaping” Kleiner word, maar hibriede tegnieke sal nog onder beskouing wees vit hulle doeltreffendheid. Die tesis bespreek ‘n algemene moment metode formulering, wat van oorvleuelende sinusoidale basisfunksies gebruik maak. Die formulering is algemeen gehou, sodat structure soos bv. ‘n monopool op ‘n sirkelvormige eindige grondvlak d.m.v. radiale drade gemodelleer kan word. Vir hierdie doel word al die komponente benodig van ‘n elektriese veld, as gevolg van ‘n stroom op ‘n draadsegment. Oor die algemeen is slegs eksplisiete uitdrukkings vir die z component van die elektriese verld in die literatuur beskikbaar. Die ander component, naamlik die ρ component (as silindriese koördinate gebruik word is die Ø component nul), moes op eie inisiatief afgelei word. Die implementering van die moment metode is vir ‘n paar geometrieë getoets om te verifier dat sekere dele van die formulering se implementering korrek is. Resultate word getoon en stem goed ooreen met ander moment metode implementerings soos FEKO en NEC. Die algemene teorie van die hibriedisering proses word daarna gegee. Om die hibriede moment/uniforme geometriese diffraksie tegnieke te illustreer, is die outeur se algemene moment metode kode gemodifiseer om die problem van ‘n monopool op ‘n sirkelvormige eindige grondvlak te kan oplos. Om hibriede tegnieke verder te illustreer, is die eenvoudige problem van ‘n dipool voor ‘n groot plaat m.b.v. FEKO opgelos. Hieruit is die voordele van die hibriede moment metode/fisiese optika of die moment metode/uniforme geometriese teorie van diffraksie duidelik getoon. ‘n Poging is daarna aangeweng om die “gaping” tussen die lae en die hoë frekwensie tegnieke te oorbrug deur ‘n praktiese problem te behandel.af_ZA
dc.description.versionMastersen_ZA
dc.format.extent85 pages : ill.en_ZA
dc.identifier.urihttp://hdl.handle.net/10019.1/55908en_ZA
dc.language.isoen_ZAen_ZA
dc.publisherStellenbosch : Stellenbosch Universityen_ZA
dc.rights.holderStellenbosch Universityen_ZA
dc.subject.lcshMoments method (Statistics)en_ZA
dc.subject.lcshElectromagnetic waves -- Diffractionen_ZA
dc.subject.lcshElectromagnetismen_ZA
dc.subject.lcshGeometrical diffractionen_ZA
dc.subject.lcshDissertations -- Engineeringen_ZA
dc.titleHybrid method of moments/uniform geometrical theory of diffraction techniquesen_ZA
dc.typeThesisen_ZA
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