The first wall 4 comprises at least one first recess 11, and the second wall 5 comprises at least one second recess 12 at least partially aligned with the first recess 11, as shown in FIGS. 3a and 4b. The first recess 11 and the second recess 12 extend perpendicular to the longitudinal extension L of the groove 7.

The first antenna array 8 comprises at least one first antenna element 8a and the second antenna array 9 comprises at least one second antenna element 9a. In one embodiment, the first antenna array 8 comprises at least two first antenna elements 8a and the second antenna array 9 comprises at least two second antenna elements 9a arranged alternately along the longitudinal extension L of the groove 7, as shown in FIGS. 2b, 3a, and 4b.

The first antenna element 8a comprises a waveguide 13 and a first signal feeding connection 14a, as shown in FIG. 3b. The waveguide 13 is formed by the first wall 4, the second wall 5, the connecting surface 6, the first surface 3a of the conductive component 3, and the second surface 3b of the conductive component 3, i.e. the waveguide 13 extends between the conductive component 3 and the first wall 4. The first signal feeding connection 14a is coupled to the first wall 4 via a galvanic connection or a capacitive coupling structure.