Van Staden, P.W.J2026-05-252026-05-251981https://hdl.handle.net/10566/22877In this thesis a short wave approximation, the method oI W Braunbek, is used to determine the diffracted fields (acoustic and electromagnetic) of plane harmonic waves by an annular aperture. Integral representations of the rigorous diffracted field in terms of the surface field and its normal derivative are derived. Babinet's theorem is proved for acoustic as well as electromagnetic plane harmonic incident waves. A derivation of Sommerfeld's solution for the diffraction of plane harmonic waves by a half-plane is includedenWave ApproximationHarmonic WavesIntegral representationsDiffracted fieldThesis