Antenna assemblies, such as RADAR or other sensor antenna assemblies for vehicles. In some embodiments, the assembly may comprise an antenna block defining a waveguide groove on a first side of the antenna block with opposing rows of posts positioned opposite from one another. A plurality of antenna slots may be positioned in the waveguide groove and may extend from the first side of the antenna block to a second side of the antenna block opposite the first side. A PCB or other means for generating electromagnetic energy may be coupled with the antenna block and be configured to feed the waveguide groove with an EM signal. The plurality of antenna slots formed in the antenna block may be configured to radiate electromagnetic energy from the antenna block.