The manipulation of spin waves in thin ferromagnetic films is a key aspect for the development of magnonic devices. Provided with unique anisotropic dispersion relations, a peculiar focused emission of spin waves, also referred to as caustic beams, occurs in in-plane magnetized films when the suitable conditions of field and frequency meets an inflection point in the dispersion relation. So far, caustic beams were solely observed in geometries where a narrow spin wave conduit reaches an extended plane, the junction acting as a diffractive source. In this communication, we extend our model of near-field diffraction of spin waves [ref] to in-plane modes, and show how caustic beams can be directly emitted from a sufficiently sharp constriction in a stripline. The obtained near-field interference patterns reproduce satisfyingly the corresponding MuMax3 micromagnetic simulations. In particular, we show that the comparison is all the better the thinner the film, as our present approach does not account for the non-reciprocity in amplitude across the thickness. This model constitutes a robust tool to explore magnon beamforming allowing probing efficiently a wide range of parameter such as field, frequency, magnetic properties, shape and scale of antenna.