Browsing by Author "Keunecke, Sven"
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- ItemHybrid method of moments/uniform geometrical theory of diffraction techniques(Stellenbosch : Stellenbosch University, 1998) Keunecke, Sven; Davidson, D. B.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH 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.