An illustrative example antenna device includes a substrate. A plurality of conductive members in the substrate establish a substrate integrated waveguide. A plurality of first and second slots are on an exterior surface of a first portion of the substrate. Each of the second slots is associated with a respective one of the first slots. The first and second slots are configured to establish a radiation pattern that varies across a beam of radiation emitted by the antenna device. A plurality of parasitic interruptions include slots on the exterior surface of a second portion of the substrate. The parasitic interruptions reduce ripple effects otherwise introduced by adjacent antennas.