An analysis of Maxwell's equations valid in a region of an ordinary wave to extraordinary wave conversion in plasmas confined by sheared and curved magnetic fields is carried out to derive an approximate system of wave equations in a three-dimensional (3D) inhomogeneous simplified stellarator-like geometry. The case is considered in which the ordinary wave cut-off surface and extraordinary wave cut-off surface, whose curvature is neglected, intersect at a point corresponding to the maximum of an incoming wave transverse distribution. The set of reduced partial differential wave equations is solved analytically by an integral representation of solutions. The form of the integral representation is justified by identifying the contour of integration. An asymptotic representation of the solution in the WKB domain is obtained that gives conversion coefficients for beams of WKB waves with a finite transverse distribution of rf field.