Diffraction by a curved impedance wedge of arbitrary angle

The methods generally considered for the diffraction by a wedge with curved faces are often different for a wedge of narrow or large angle. An original approach, initiated by J.M.L. Bernard (see Rev. Tech. Th., vol.23, no.2, p.321-30, 1991) for faces of constant curvatures and whose results have been recently used by V.A. Borovikov (see J. Comm. Techn. Elect., vol.43, no.12, p.1337-46, 1998) for his developments on the non constant curvature case, permits a new global asymptotic study for an impedance curved wedge of any angle. We reduce the boundary problem on the field to an asymptotic one on the spectral function, related to the representation of the field in the form of a Sommerfeld-Maliuzhinets integral. The functional equations then obtained can he solved, and the asymptotics of the spectral function are developed (see Bernard, 1991). We present a new form of it. An expression allowing the transition to an asymptotic expansion with fractional powers is also given for directions close to the tangent at the faces, where creeping waves excited by the edge propagate. We note that the general expressions here given allow the recovery of all known results on diffraction coefficients for particular wedge angles, from the case of a discontinuity of curvature to the case of a curved half plane.