Embodiments are disclosed of an orthomode transducer (OMT) device for splitting a linear orthogonally polarized electromagnetic signal into a plurality of linearly polarized frequency components and vice versa. The device comprises a rectangular or circular guide section having a constant cross-section perpendicular to a lengthwise direction of said guide section and first and second lengthwise opposed open ends, a septum that is successively increased in height; extending from an end of the a waveguide portion towards a second lengthwise open end of the guide section, wherein that the plane of said septum is provided at an angle of 45 degrees relative to the polarization axes of the orthogonal linear polarization modes and said septum induces a differential phase shift of substantially 180 degrees or a multiple thereof between components of the linear polarization modes that are perpendicular to said septum and components that are parallel to said septum.