An antenna device, comprising: a substrate comprising a first side with an exterior surface including a layer of electrically conductive material and a conductive layer near an opposite side of the substrate; a plurality of conductive members (26, 36, 46) in the substrate, the conductive members (26, 36, 46) establishing a substrate integrated waveguide, SIW, (24, 34, 44), a first portion of the substrate being within the SIW (24, 34, 44) and a second portion of the substrate being outside the SIW (24, 34, 44); a plurality of first slots on the exterior surface of the first portion of the substrate, the first slots having a first length; a plurality of second slots on the exterior surface of the first portion of the substrate, each of the second slots being associated with a respective one of the first slots, the first and second slots (52, 54) being configured to establish a radiation pattern that varies across a beam of radiation emitted by the antenna device, the second slots having a second length, the first length being longer than the second length; and a plurality of parasitic interruptions, at least a first one of the parasitic interruptions being on a first side of the SIW (24, 34, 44) and at least a second one of the parasitic interruptions being on the opposite side of the SIW (24, 34, 44), wherein: the first one of the parasitic interruptions comprises a first set of one or more first parasitic-interruption slots formed along the exterior surface of the second portion of the substrate and at least one conductive connector establishing a conductive connection between the exterior surface of the second portion near two sides of the respective first parasitic-interruption slots and the conductive layer near the opposite side of the substrate; the second one of the parasitic interruptions comprises a second set of one or more second parasitic-interruption slots formed along the exterior surface of the second portion of the substrate and at least one further conductive connector establishing a further conductive connection between the exterior surface of the second portion near two sides of the respective second parasitic-interruption slots and the conductive layer near the opposite side of the substrate; and the first set and the second set having a different number of respective parasitic-interruption slots. a substrate comprising a first side with an exterior surface including a layer of electrically conductive material and a conductive layer near an opposite side of the substrate; a plurality of conductive members (26, 36, 46) in the substrate, the conductive members (26, 36, 46) establishing a substrate integrated waveguide, SIW, (24, 34, 44), a first portion of the substrate being within the SIW (24, 34, 44) and a second portion of the substrate being outside the SIW (24, 34, 44); a plurality of first slots on the exterior surface of the first portion of the substrate, the first slots having a first length; a plurality of second slots on the exterior surface of the first portion of the substrate, each of the second slots being associated with a respective one of the first slots, the first and second slots (52, 54) being configured to establish a radiation pattern that varies across a beam of radiation emitted by the antenna device, the second slots having a second length, the first length being longer than the second length; and a plurality of parasitic interruptions, at least a first one of the parasitic interruptions being on a first side of the SIW (24, 34, 44) and at least a second one of the parasitic interruptions being on the opposite side of the SIW (24, 34, 44), wherein: the first one of the parasitic interruptions comprises a first set of one or more first parasitic-interruption slots formed along the exterior surface of the second portion of the substrate and at least one conductive connector establishing a conductive connection between the exterior surface of the second portion near two sides of the respective first parasitic-interruption slots and the conductive layer near the opposite side of the substrate; the second one of the parasitic interruptions comprises a second set of one or more second parasitic-interruption slots formed along the exterior surface of the second portion of the substrate and at least one further conductive connector establishing a further conductive connection between the exterior surface of the second portion near two sides of the respective second parasitic-interruption slots and the conductive layer near the opposite side of the substrate; and the first set and the second set having a different number of respective parasitic-interruption slots.