An E-plane directional coupler for coupling an electromagnetic signal from an open end of the directional coupler to a plurality of open ends of the directional coupler, the directional coupler comprising: - two hollow bodies (200, 201) forming two waveguide portions, each hollow body having an open end arranged at a first side of the hollow body and another open end arranged at a second side of the hollow body opposite to the first side in a longitudinal direction of the hollow body, the hollow body having a first cross section perpendicular to the longitudinal direction, a second cross section along the longitudinal direction for defining the E-plane of propagation of the electric field, the two waveguide portions having a common wall along the longitudinal direction and arranged between two opposite second walls of the waveguide portions, the common wall forming a septum between the two waveguide portions on a second plane orthogonal to the E-plane, the septum having a single aperture for coupling the two waveguide portions, the aperture having a shape comprising a slanted part with respect to the longitudinal direction, wherein the aperture is configured to couple part of a power of the electromagnetic signal, which is coupled into the directional coupler at the open end of a first one of the two waveguide portions and which has a fundamental mode of propagation with a half-wave pattern across a width of said first waveguide portion, via the aperture into a second one of the two waveguide portions to excite an orthogonal mode of propagation of the electromagnetic signal with a half-wave pattern across a height of said second waveguide portion, wherein the shape of the aperture comprises, as consecutively connected parts: a first part extending from one of the second walls in a direction perpendicular or quasi perpendicular to the longitudinal direction, - the slanted part being a first slanted part having a first slope slanting away from the one of the second walls with respect to the longitudinal direction, - a second slanted part having a second slope opposite to the first slope with respect to the longitudinal direction, - a second part extending to the one of the second walls in a direction perpendicular or quasi perpendicular to the longitudinal direction, wherein said consecutively connected parts do not completely extend between the second walls. - two hollow bodies (200, 201) forming two waveguide portions, each hollow body having an open end arranged at a first side of the hollow body and another open end arranged at a second side of the hollow body opposite to the first side in a longitudinal direction of the hollow body, the hollow body having a first cross section perpendicular to the longitudinal direction, a second cross section along the longitudinal direction for defining the E-plane of propagation of the electric field, the septum having a single aperture for coupling the two waveguide portions, the aperture having a shape comprising a slanted part with respect to the longitudinal direction, wherein the aperture is configured to couple part of a power of the electromagnetic signal, which is coupled into the directional coupler at the open end of a first one of the two waveguide portions and which has a fundamental mode of propagation with a half-wave pattern across a width of said first waveguide portion, via the aperture into a second one of the two waveguide portions to excite an orthogonal mode of propagation of the electromagnetic signal with a half-wave pattern across a height of said second waveguide portion, wherein the shape of the aperture comprises, as consecutively connected parts: a first part extending from one of the second walls in a direction perpendicular or quasi perpendicular to the longitudinal direction, - the slanted part being a first slanted part having a first slope slanting away from the one of the second walls with respect to the longitudinal direction, - a second slanted part having a second slope opposite to the first slope with respect to the longitudinal direction, - a second part extending to the one of the second walls in a direction perpendicular or quasi perpendicular to the longitudinal direction, a first part extending from one of the second walls in a direction perpendicular or quasi perpendicular to the longitudinal direction, - the slanted part being a first slanted part having a first slope slanting away from the one of the second walls with respect to the longitudinal direction, - a second slanted part having a second slope opposite to the first slope with respect to the longitudinal direction, - a second part extending to the one of the second walls in a direction perpendicular or quasi perpendicular to the longitudinal direction, wherein said consecutively connected parts do not completely extend between the second walls.