A waveguide twist for rotating the polarisation plane consists of rectangular hollow conductors wound constantly about its axis, but which require a not inconsiderable constructional length. In a conventional polarisation filter, although it is possible for the propagation direction to be positioned mutually parallel using an elbow, the polarisation planes are however rotated by 90 DEG in the two waveguide branches. In order to provide a waveguide twist, especially for use in a polarisation filter having a small space requirement, with simple means, it is provided that two parallel adjacent waveguides are connected to one another via a common coupling window which is arranged centrally in the one waveguide in the longitudinal direction and off-centre in the other waveguide.; When two rectangular waveguides are employed, the coupling window is arranged on the one hand centrally on the narrow side and off-centre on the wide side on the other waveguide. The waveguide twist is also especially suitable for polarisation filters.